International Journal of Neuropsychopharmacology (2022) 25(1): 13–25 https://doi.org/10.1093/ijnp/pyab051 Advance Access Publication: 2 September 2021 Regular Research Article Regular Research Article Effects of Mixing Energy Drinks With Alcohol on Driving-Related Skills Clara Pérez-Mañá, Julián Andrés Mateus, Patricia Díaz-Pellicer, Ariadna Díaz-Baggerman, Marta Pérez, Mitona Pujadas, Francina Fonseca, Esther Papaseit, Jesús Pujol, Klaus Langohr, Rafael de la Torre Clinical Pharmacology Unit, Hospital Universitari Germans Trias i Pujol (HUGTP-IGTP), Badalona, Spain (Drs Pérez-Mañá and Papaseit); Integrative Pharmacology and Systems Neurosciences Research Group, Neurosciences Research Program, Hospital del Mar Medical Research Institute (IMIM), Barcelona, Spain (Dr Pérez-Mañá, Dr Mateus, Ms Díaz-Pellicer, Ms Pérez, Ms Pujadas, Dr Langohr, and Dr de la Torre); Department of Pharmacology, Therapeutics and Toxicology, Autonomous University of Barcelona (UAB), Cerdanyola del Vallès, Spain (Drs Pérez-Mañá, Mateus, and Papaseit); Neurosciences Master, University of Barcelona (UB), Barcelona, Spain (Ms Díaz-Baggerman); Drug Addiction Unit, Institute of Neuropsychiatry and Addictions (INAD), Hospital del Mar Medical Research Institute (IMIM), Barcelona, Spain (Dr Fonseca); MRI Research Unit, Hospital del Mar, CIBERSAM G21, Barcelona, Spain (Dr Pujol); Department of Statistics and Operations Research, Polytechnic University of Catalonia/BarcelonaTech, Barcelona, Spain (Dr Langohr); Pompeu Fabra University (CEXS-UPF), Barcelona, Spain (Dr de la Torre); CIBER de Fisiopatología Obesidad y Nutrición (CIBEROBN), Instituto de Salud Carlos III, Madrid, Spain (Dr de la Torre). Correspondence: Clara Pérez-Mañá, MD, PhD, Carretera de Canyet, S/N, 08916 Badalona, Barcelona, Spain (cperezm.mn.ics@gencat.cat). Abstract Background: Energy drinks (EDs) reduce sleepiness and fatigue and improve driving performance whereas alcohol does just the opposite. Although it is a trendy combination among young people, the effects of alcohol mixed with EDs on driving performance have been poorly studied. The aim was to assess if there is an interaction between the effects of both drinks on driving-related skills as well as perceptions about driving ability. Methods: We conducted a randomized, double-blind, and placebo-controlled 4-way crossover clinical trial. Participants were 16 healthy volunteers. Interventions of 60 g of ethanol and 750 mL of Red Bull (RB) were administered in 2 separated doses. Conditions were alcohol + RB placebo, alcohol + RB, alcohol placebo + RB, and both placebos. Objective performance was assessed using a tracking test and simple reaction time, N-Back, and movement estimation tasks. Additionally, willingness to drive, other subjective effects, and ethanol and caffeine blood concentrations were also measured. Results: Alcohol increased the time outside the road in the tracking test and increased simple reaction time, but the addition of RB had no main or interaction effects on performance. Nonetheless, driving-related skills after alcohol + RB were better than after alcohol alone. Willingness to drive increased with the combination of drinks. RB also reduced alcohol-induced sedation whereas drunkenness did not change. These effects were seen even though alcohol + RB increased alcohol (14.8%) and caffeine plasma concentrations (17.6%). Conclusions: Mixing EDs with alcohol predisposes consumers to drive under alcohol influence, perhaps in part because EDs counteract its detrimental effects on driving-related skills. Clinicaltrials.gov: NCT02771587. Received: November 13, 2020; Revised: June 16, 2021; Accepted: July 26, 2021 © The Author(s) 2021. Published by Oxford University Press on behalf of CINP. This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (https://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any 13 medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com 14 | International Journal of Neuropsychopharmacology, 2022 Significance Statement Consumption of energy drinks (EDs) with alcohol has become trendy among young people. The stimulant effects of caffeine in these drinks may predispose users to underestimate the extent of their alcohol-induced impairment. In this study, mixing 3 ED with alcohol reduced sedation and increased willingness to drive compared with alcohol alone. Alcohol impaired driving per- formance more than the combination of alcohol + EDs. Altogether these results suggest that consumers are at risk when driving under their influence. Furthermore, a modest increase in caffeine and alcohol concentrations was observed with the combin- ation of EDs with alcohol. Mechanisms involved should be further investigated. Keywords: Alcohol, energy drinks, caffeine, interaction, driving-related skills, pharmacokinetics, addiction Introduction For most individuals, alcohol is the most consumed drug in Consumers of AmED have been reported to reach a state that the last month (Global Drug Survey, 2019), and acute alcohol has been called “wide-awake drunkenness” (Pennay et al., 2015). impairment still remains a societal problem with severe con- They report greater prolonged sessions of heavy alcohol con- sequences to the user and those around them. In addition to sumption and engagement in risk-taking behaviors, showing a traffic accidents, alcohol consumption can turn into alcoholism greater likelihood of alcohol-related unsafe driving (Martz et al., and is a risk factor for mental and behavioral disorders, liver cir- 2015). Their higher rates of impaired driving could be explained rhosis, some cancers, and cardiovascular diseases (World Health by an erroneous perception of increased driving ability that Organization, 2018). Almost one-half of students in Europe re- contradicts objective performance outcomes (Marczinski et al., port alcohol current use (ESPAD, 2019). 2018). Experimental data, however, do not clearly support those Energy drinks (EDs) contain principally caffeine, but also surveys (Peacock et al., 2014; Verster et al., 2018). taurine, vitamin B complex, vegetal extracts (guarana, ginseng), Regarding impact on cognition, some studies have shown sugar, and artificial sweeteners. ED consumers use these drinks that EDs counteract some alcohol-induced cognitive deficits, to bring them energy, reduce tiredness and fatigue, and increase depending on the alcohol dose, concentration, and limb of the intellectual capacity (Ravelo et al., 2013). EDs are commonly used blood alcohol time course (T-C) curve, but these effects are as a source of dietary supplements, but there is less knowledge partial or disappear with complex tasks (McKetin et al., 2015; of their health-related harms, such as the potential relationship Lalanne et al., 2017). with cardiovascular diseases (Mangi et al., 2017), compared with Few studies have assessed effects of caffeinated beverages other substances (Pacifici et al., 2016). In a national survey con- on driving performance. In experimental studies, an ED (80 mg ducted in the United States (Mitchell et al., 2014), the greatest caffeine) significantly improved driving performance and re- prevalence of ED consumption was found among 13– to 24–year– duced driver sleepiness during prolonged highway driving olds. In Europe, 13% of daily caffeine intake among adolescent (Mets et al., 2011), and 2 EDs facilitated lower-lane position de- ED consumers came from these drinks (Zucconi et al., 2013). viations and reduced steering wheel deviations in truck drivers Consumption of alcohol with EDs (AmED) is popular among (Ronen et al., 2014). Mixed with alcohol, caffeine capsules (200 or young people, either as a mixed cocktail or in the same drinking 400 mg) partially counteracted alcohol-induced impairment in session (Arria et al., 2016). Surveys conducted in Europe report brake latency, but performance remained more impaired when that 48% of university students using EDs had consumed them alcohol was present (0.6 g/kg of alcohol) (Liguori and Robinson, with alcohol (Oteri et al., 2007), and 1 in 4 youth in the United 2001). Another study with caffeinated and un-caffeinated beer States and Canada consumed AmED during the last year (Martz (average caffeine and alcohol doses of 383 mg and 1 g/kg, re- et al., 2015; Wilson et al., 2018). Furthermore, adolescents who spectively) showed no improvement of driving performance regularly drink AmED more often binge drink (O’Brien et al., (speed, lane position, and crashes) with the addition of caffeine 2008). (Howland et al., 2011). Finally, EDs decreased alcohol induced- Alcohol produces perception-sensorium impairments like impairment in a tracking test, mainly when alcohol concentra- visual deficits, loss of perception in movements, reduced cap- tions were in the descending limb of the blood alcohol T-C curve acity of attention, false security, and impulsivity. Drivers under (Peacock et al., 2015). Those studies matched performance with the influence of alcohol are more susceptible to be cited for breath alcohol concentrations (BrAC). traffic violations and to have traffic accidents (Directorate- The main aim of the study was to assess if there is an inter- General for Traffic, 2016). This problem is particularly important action between the effects of alcohol and EDs on driving-related in the young population, where there are many erroneous be- skills. liefs about actions to mitigate the effects of alcohol on driving (Olivera et al., 2002). On the other hand, studies have demonstrated that con- MATERIALS AND METHODS suming EDs before driving would have positive effects, reducing Participants somnolence in long travels and augmenting alertness (Mets et al., 2011; Ronen et al., 2014). Consumers of AmED report use Participants needed to be healthy and consumers of at least to reduce drunkenness, but only 1 study showed a reduction 1 Standard Unit (SU)/d (10 g of alcohol in Spain), with several of subjective intoxication (Marczinski et al., 2006) and other previous acute drunkenness experiences (≥once monthly), with studies failed to show a masking effect of EDs (Benson et al., a body mass index between 19 and 27 kg/m2 and weight be- 2014; Verster et al., 2018). tween 50 and 100 kg. A minimum consumption of 5 drinks/wk Pérez-Mañá et al. | 15 containing methylxanthines and a driving license were also re- study was the change in the TimeOut. Detailed information of quired. See exclusion criteria in supplementary Materials. tests is included in supplementary Materials. Treatments Subjective Effects Rating Scales Alcohol was administered as Vodka Absolut (40º alcohol) at a dose Several visual analog scales (VAS), Biphasic Alcohol Effects Scale of 30 g (94 mL of vodka), and its placebo was Fontvella water. The (BAES) (Martin et al., 1993), and the Spanish validated version of ED used was lime-flavor Red Bull (RB) at a dose of 375 mL (1.5 the short-form Addiction Research Center Inventory (ARCI) were cans), and its placebo was Seven-Up. Every can of RB contained used (Lamas et al., 1994). 80 mg of caffeine and 1 g of taurine. The flavor and the content of VAS (0–100 mm) marked at opposite end with “not at all” and carbohydrates (every 100 mL contains 11 g) of RB and its placebo “extremely” included assessment of drunkenness, dizziness, were similar. Two doses were administered (1 hour of separation drowsiness, palpitations, anxiety, and headache. Additionally between them), so participants received a total of 60 g of alcohol capability to drive and willingness to drive under various emo- (188 mL of vodka) and 750 mL of RB (3 cans, 240 mg of caffeine). tional and rewarding circumstances (“taking an ill child to the Every dose was served cold and distributed in 3 opaque cups and hospital,” “an indisposed friend home,” and “a friend to a party”) ingested in a period of 15 minutes (5 min/cup). The total doses were measured at baseline and 0.5, 2, 4, 6, and 8 hours after first selected in the study correspond to 6 SU in Spain, 7.5 SU in England, administration (Ménétrey et al., 2005). and a bit more than 4 SU in the United States. Randomization and BAES evaluates subjective ratings of activation (BAES-A) and treatments were prepared by a person not involved in the experi- sedation (BAES-S) using a 14-adjective rating scale (7 adjectives mental sessions. The fact that alcohol was quite diluted, the mixer for stimulation and 7 for sedation). A Likert scale ranging from 0 was very sweet, the lime flavor, the cold and the opaque cups con- (no at all) to 10 (extremely) is used, and stimulation and sedation tributed to mask the treatment conditions. scores were summed separately (score subscale range = 0–70). ARCI is a true/false 49-item questionnaire used to as- Study Design sess drug effects with 5 subscales: PCAG (pentobarbital- chlorpromazine-alcohol group, a measure of sedation), MBG The study was double-blind and placebo-controlled. Individuals (morphine-benzedrine group, a measure of euphoria), LSD (ly- participated in four 8-hour experimental sessions with a sergic acid diethylamide group, a measure of dysphoria and minimum 3-day washout period. Treatments were randomly as- somatic symptoms), BG (benzedrine group, a stimulant subscale signed using a balanced 4 × 4 Latin-square design: (a) alcohol related to intellectual efficiency and energy), and A (amphet- + RB placebo, (b) alcohol + RB, (c) alcohol placebo + RB, and (d) amine, a measure of d-amphetamine effects). alcohol placebo + RB placebo. Alcohol, drinks with methylxanthines, and meals rich in Concentrations taurine were prohibited 72 hours before until 24 hours after administration. Every session day, participants arrived to the BrAC were measured at baseline and 0.75, 1, 1.5, 1.75, 2, 2.25, 2.5, Parc de Salut Mar Clinical Research Unit at 07:45 am after an 3, 4, and 8 hours (Dräger Breathalyzer 7410 Plus, Denmark). Blood overnight fast. An indwelling intravenous catheter was inserted alcohol concentrations (BAC) were measured additionally at 0.25, into a subcutaneous vein of the non-dominant arm to obtain 0.50, and 6 hours. Caffeine and taurine plasma concentrations blood samples. Doses were administered at 8:30 and 9:30 am. were measured at 0, 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, and 8 hours. Caffeine Participants remained in beds in a calm environment and psy- and caffeine metabolite concentrations were measured in urine. chomotor tests were performed in a separate room. Urine gener- ated was collected until 8 hours after administration. Breakfast Vital Signs and Adverse Events was ingested at 3 hours and consisted of a turkey sandwich with 150 mL of water and the meal included pasta, chicken with Safety and tolerability of drinks were assessed. Systolic and salad, an apple, and 330 mL of water at 6 hours. diastolic blood pressure, heart rate, and oral temperature were measured at baseline and 0.5, 1, 1.5, 2, 2.5, 4, 6, and 8 hours. Driving-Related Skills Adverse events were also recorded. The battery included a Tracking Test (TT), Simple Reaction Analytical Assays Time task (SRT), N-Back task (NB), and Movement Estimation task (MET). These tests were performed along 20 minutes at Alcohol concentrations were determined using the enzymatic baseline and 0.5 (between doses), 2, and 4 hours after admin- assay DRI Ethyl Alcohol Assay (Thermo Fisher, Fremont, CA, USA) istration of the first dose, using a laptop and the Cambridge with a cut-off point of 10 mg/dL. Taurine and caffeine were sim- Neuropsychological Test Automated Battery. Participants were ultaneously analyzed in plasma by Liquid Chromatography with trained at screening. tandem Mass Spectrometry (LC-MS-MS). Caffeine, paraxanthine, The TT used is an adaptation of the classic Critical Tracking theobromine, and theophylline were analyzed in urine by Gas Task (Jex et al., 1966), very similar to the Visuomotor Bimanual Chromatography-Mass Spectrometry (GC/MS). Details on the Coordination Test used in Spain to obtain the driving license method are in supplementary Materials. (Gombao et al., 2006). It is an interactive task of 290 seconds that requires individuals to maintain 2 yellow vehicles circulating in Ethical Aspects the middle of 2 roads. Each vehicle is controlled by 1 hand with a joystick. It allows registering TimeOut (the total time when a The study protocol and information sheet were approved vehicle is outside of the road), the number of errors (times that by the Clinical Research Ethics Committee of Parc de Salut a car goes off the road more than 0.4 seconds) and the number Mar (CEIm-Parc de Salut Mar approval no. 2015/6361/I). The of gyres (changes in joystick direction). The main outcome of the study was conducted according to the Declaration of Helsinki 16 | International Journal of Neuropsychopharmacology, 2022 and each participant signed an informed consent prior to participation. The study was registered in clinicaltrials. gov. Participants were compensated with 625 Euros for their participation. Statistical Analysis Differences to baseline and the following pharmacokinetic parameters were calculated for all outcomes: area under the curve of the concentrations and effects (AUC), the time needed to reach the maximum concentration and effect (tmax) and the maximum concentration (Cmax) and effect (peak or Emax). AUC and Emax were compared using a 2 (alcohol: active, placebo) × 2 (RB: active, placebo) factorial repeated-measures ANOVA. The interaction term was used as indicative of the cap- acity of RB to affect the effect of alcohol. When the alcohol × RB interaction was statistically significant, multiple post-hoc comparisons were performed among the 4 conditions using the Tukey’s test. In addition, these models were used to estimate the substance effects of alcohol and RB (vs placebo), respect- ively. For tmax, the Friedman’s test and Wilcoxon’s test were used. Concentrations were compared by a paired Student’s t test (AUC and Cmax) and a Wilcoxon’s test (tmax). Furthermore, a detailed comparison of T-C of effects was conducted using repeated- measures 2-way ANOVA, with treatment condition and time as factors. When the treatment condition × time interaction was statistically significant, multiple Tukey post-hoc comparisons between the 4 conditions were performed at each time point. Repeated-measures correlations were calculated to assess the within-individual associations between alcohol concentrations and effects at the different points (Bakdash and Marusich, 2017). Statistical analysis was performed using PAWS Statistics ver- sion 18 (SPSS Inc., Chicago, IL, USA) and R Statistical Software (Vienna, Austria; https://www.r-project.org/), version 4.0.2. A value of P <.05 was considered statistically significant. RESULTS Study Participants A total of 16 healthy male participants were included in the study (see supplemental Figure 1). Participants mean and SD age was 24.0 ± 5.2 years (range 19–29 years), weighed 72.6 ± 10.1 kg, and their body mass index was 23.4 ± 2.3 kg/m2. All but 4 participants were non-smokers. Their average alcohol and methylxanthine consumption was 1.8 ± 0.8 SU/d, and 1.9 ± 0.8 drinks/d, respectively. Their average consumption of EDs was 9.9 ± 15.4 cans in the last year and 37.7 ± 42.7 cans throughout life. Taking into account participants’ weight, average alcohol and caffeine doses administered were 0.8 g/kg and 3.4 mg/kg, respectively. Figure 1. Time course of effects for driving-related skills (differences to base- Driving-Related Skills line). Data points and error bars represent mean and SD values for 16 partici- pants. Conditions: alcohol (60 g); alcohol (60 g) + RB (240 mg caffeine); RB (240 mg Main results are shown in Figure 1. Table 1 shows pharmaco- caffeine); placebo. * P < .05 and ** P < .01 indicate alcohol significant differences dynamic parameters. with A/RB. Filled symbols indicate a significant difference from placebo (P < .05). The significance is only reported for the comparison of more interest (A vs A/ TT.—Alcohol significantly increased TimeOut while RB had no RB) and also between all conditions and placebo. Other comparisons are not in- main or interaction effects (peak and AUC). In the T-C alcohol cluded in the figure to make it easy to understand. increased TimeOut in comparison with placebo at all time points while differences among both conditions with alcohol SRT.—A main effect of alcohol was found in mean latency, which were found at 2 hours. The combination of alcohol + RB reduced increased with alcohol consumption, while RB had no main or TimeOut compared with alcohol alone. The same results were interaction effects (peak and AUC). In the T-C, RB counteracted found for the number of errors. alcohol effects at 2 hours (see Figure 1). The maximum effects Table 1. Driving-Related Skills Pharmacodynamic Parameters’ Statistical Analysis A A/RB RB P ES (95% CI) ES (95% CI) Inter- Outcomes Mean ± SD Mean ± SD Mean ± SD Mean ± SD Parameter Alcohol RB action Time out 3.81 ± 6.37 −0.34 ± 3.25 −1.52 ± 2.93 0.86 ± 3.51 Peak 2.9 −2.4 N.S. (−0.4 to 6.3) (−5.7 to 0.9) N.S. N.S (TT) s 10.54 ± 16.49 −0.36 ± 5.60 −4.10 ± 7.41 −0.49 ± 9.03 AUC0-4h 11.0 −3.6 N.S. (2.8 to 19.2)** (11.8 to 4.5) N.S. Errors 5.25 ± 7.50 0.88 ± 4.46 −1.75 ± 3.00 −0.31 ± 3.50 Peak 5.6 −1.4 N.S. (1.8 to 9.3)** (−5.2 to 2.3) N.S. (TT) 15.45 ± 21.53 2.13 ± 7.43 −5.03 ± 6.73 −0.09 ± 6.93 AUC0-4h 15.5 −4.9 N.S. (6.0 to 25.1) ** (−14.4 to 4.6) N.S. Gyre 67 ± 99.57 20.31 ± 122.90 −12.00 ± 88.64 4.38 ± 102.74 Peak 62.5 −16.4 N.S. (−15.2 to 140.5) N.S (−94.2 to 61.5) N.S. (TT) 179.31 ± 263.40 65.06 ± 299.4 25.08 ± 200.81 91.44 ± 213.24 AUC0-4h 87.9 −66.4 N.S. (−92.4 to 268.1) N.S. (−246.6 to 113.9) N.S. Latency 43.21 ± 34.20 8.89 ± 28.41 −17.19 ± 18.84 −0.04 ± 30.40 Peak 43.3 −17.2 N.S. (22.4 to 64.1)*** (−38.0 to 3.7) N.S. (SRT) ms 93.73 ± 71.49 14.26 ± 52.57 −29.83 ± 45.96 1.73 ± 72.94 AUC 0-4h 92.0 −31.6 N.S. (45.1 to 138.9)*** (−78.5 to 15.4) N.S. Latency SD 42.63 ± 37.70 15.89 ± 24.70 −6.86 ± 26.64 2.48 ± 28.50 Peak 40.1 −9.3 N.S. (18.3 to 62.0)*** (−31.2 to 12.5) N.S. (SRT) 98.26 ± 81.81 33.43 ± 52.08 −17.18 ± 58.32 2.18 ± 66.22 AUC0-4h 96.1 −19.3 N.S. (44.9 to 147.4)*** (−70.6 to 31.9) N.S. Absolute error 0.06 ± 0.23 −0.05 ± 0.33 −0.03 ± 0.26 −0.03 ± 0.29 Peak 0.1 0.0 N.S (−0.1 to 0.3) N.S. (−0.2 to 0.2) N.S. Time (MET) s 0.11 ± 0.45 −0.19 ± 0.76 −0.10 ± 0.61 −0.01 ± 0.66 AUC0-4h 0.1 −0.1 N.S. (−0.4 to 0.6) N.S. (−0.6 to 0.4) N.S. Missings 0.13 ± 1.96 0.19 ± 1.05 0.00 ± 0.97 0.38 ± 1.50 Peak −0.3 −0.4 N.S (−0.9 to 0.8) N.S. (−1.5 to 0.7) N.S. (MET) −0.84 ± 4.92 0.23 ± 2.80 −0.50 ± 2.40 2.34 ± 3.35 AUC0-4h −3.2 −2.8 * (−5.9 to −0.5)* (−5.6 to −0.1)* Hits −0.88 ± 5.70 −1.50 ± 6.38 −1.88 ± 3.96 −0.69 ± 5.10 Peak −0.2 −1.2 N.S. (−4.0 to 3.7) N.S. (2.7 to 0.7) N.S. (NB) −0.42 ± 13.00 −1.48 ± 11.92 −1.84 ± 6.95 0.80 ± 10.37 AUC0-4h −1.2 −2.6 N.S. (−9.5 to 7.1) N.S. (−10.9 to 5.6) N.S. Errors 0.19 ± 5.75 1.31 ± 6.43 0.44 ± 3.46 −0.13 ± 4.90 Peak 0.3 0.6 N.S. (−3.2 to 3.7) N.S. (−2.9 to 4.0) N.S. (NB) −1.22 ± 14.14 0.91 ± 12.00 0.72 ± 5.92 −1.94 ± 10.24 AUC0-4h 0.7 2.7 N.S. (−7.1 to 8.5) N.S. (−5.1 to 10.4) N.S. Reaction time −0.02 ± 0.11 0.00 ± 0.99 −0.03 ± 0.10 −0.04 ± 0.14 Peak 0.0 0.0 N.S. (−0.1 to 0.1) N.S. (−0.1 to 0.1) N.S. (NB) s 0.06 ± 0.17 −0.05 ± 0.17 −0.05 ± 0.20 −0.03 ± 0.24 AUC0-4h 0.1 −0.1 N.S Pérez-Mañá et al. | (−0.1 to 0.3) N.S. (−0.3 to 0.10) N.S. 17 Abbreviations: A, alcohol + placebo energy drink; A/RB, alcohol + Red Bull; AUC, area under the curve; CI, confidence interval; ES, estimated substance effect; MET, movement estimation task; ms, millisecond, NB, N-Back task; P, placebo alcohol + placebo Red Bull; RB, Red Bull + placebo alcohol; SD, standard deviation; s,second; TimeOut, time outside the road; TT, tracking test; SRT, simple reaction time. N.S. mean not significant. * P < .05; ** P < .01; *** P < .001. 18 | International Journal of Neuropsychopharmacology, 2022 were 43.2 ± 34.2 ms for alcohol and 8.9 ± 28.4 ms for A/RB. Concentrations Differences in the same direction were found for latency SD. Commission errors were 2.6, 2.2, 0.6, and 1.2 for alcohol, A/RB, Pharmacokinetic parameters are summarized in Table 3 and T-C RB, and placebo, respectively, 2 hours after administration (not of concentrations in Figure 3. significant). Also no differences were found in the number of omission errors and correct responses. Alcohol.—BACs were detected during 8 hours. Cmax was reached around 2 hours after the first administration. Peak BAC with alcohol alone was 0.7 g/L with the multiple dose (30 g + 30 g), NB.—One volunteer was excluded due to outlying scores. No while theoretical BAC from a single dose of 60 g for a 73 kg statistically significant differences were found between all participant is 1.17g/L. Alcohol concentrations were higher with conditions in this task. A/RB. Mean increases of 14.8% and 13.2% were found in AUC and Cmax, respectively. Differences were mainly observed from 0.25 MET.—Absolute error time increased 60 ms with alcohol and was to 2.5 hours. Driving related-skills assessments were conducted reduced 50, 30, and 30 ms for A/RB, RB, and placebo conditions, with a mean BAC of 0.22 g/L (0.5 hour), 0.60 g/L (2 hours), and respectively. When the absolute error was calculated taking into 0.40 g/L (4 hours). account the sign (anticipation or delay), placebo error time was Regarding BrAC, similar peak values were obtained (0.38 mg/L +180 ms while it was −70, −100, and −50 ms, for alcohol, A/RB, for alcohol and 0.40 mg/L for A/RB), and no differences were and RB, respectively (not statistically significant). found among conditions. The T-C for BrAC was very similar to BAC, and concentrations in both matrices were strongly correl- ated (correlation coefficients of 0.96, see Table 5). Subjective Effects Results of pharmacodynamic parameters are shown in Table 2. Caffeine and Taurine.—Caffeine concentrations in blood were Data about T-C for selected outcomes is included in Figure 2. higher when alcohol was present, from 1 to 8 hours. A mean In general terms, subjective effects reached their peak 1.5-2.5 increase of 17.6% was found in AUC0-8h and of 12.7% in Cmax. No hours after administration and returned to baseline from 4 to differences in taurine concentrations were observed between 8 hours later. both RB conditions. Subjective Intoxication and Other Subjective Outcomes (VAS).—A Caffeine and Caffeine Metabolites in Urine.—Data from 1 volunteer total 60 g of alcohol with or without RB produced mild-moderate were excluded due to outlying concentrations. Results showed drunkenness. Drunkenness sensation was similar among both higher recoveries of paraxanthine and lower recoveries of alcoholic conditions, being slightly lower with A/RB at 2 hours. caffeine with RB than with A/RB from 0 to 8 hours. Furthermore, Furthermore, no interaction effects of RB and alcohol were found higher recoveries of theophylline were found in the absence of in peak or AUC values. Alcohol induced moderate drowsiness ethanol. The volume of urine generated was higher with A/RB compared with other treatments, whereas A/RB reduced it to (1981.9 ± 349.5 mL) than in the other experimental conditions one-half. In this outcome, an interaction effect of RB with alcohol (1642.5 ± 368.5 mL for alcohol, 1581.6 ± 338.5 mL for RB, and was found (peak and AUC). The 2 alcohol conditions produced 1420.0 ± 358.3 mL for placebo). slight dizziness whereas none of the beverages administered produced significant palpitations, anxiety, or headache. Vital Signs and Adverse Events Capability to Drive and Willingness to Drive.—Data were obtained Results are shown in Table 4. Systolic blood pressure increased until 4 hours for the first 8 volunteers and until 8 hours for the last mainly with RB conditions in the first 2.5 hours, but no main 8 volunteers. Alcohol and A/RB reduced subjective capability to or interaction effects were found (peak and AUC). RB increased drive and reduced willingness to drive in all the driving situations diastolic blood pressure the first 2.5 hours (RB main effects in proposed. Participants were more willing to drive under A/RB peak and AUC values). In the T-C, blood pressure with A/RB was compared with alcohol alone. There was an alcohol main effect significantly higher than with alcohol (1– 2.5 hours). Regarding for all these outcomes, and an interaction effect for RB was heart rate, T-C showed an increase with both alcoholic condi- found in AUC. In the T-C, differences among both conditions with tions across 8 hours with no differences among them. A main alcohol appeared until 4 hours after administration (n = 8). effect of alcohol was found (peak and AUC). No differences were found in oral temperature. BAES.—In the first 3 hours, participants rated stimulation and A total of 12 nonserious adverse events were registered in sedation and from then only rated sedation. A main effect of 7 volunteers, and 8 adverse events were considered possibly or alcohol was found for both BAES subscales. RB reduced alcohol- probably related to treatment (headache and gastrointestinal induced sedation (interaction effect found in AUC). In the T-C, symptoms). differences between both alcoholic conditions appeared from 1.5 to 3 hours for stimulation and from 1 to 4 hours for sedation. Relationship Between Concentrations and Effects ARCI.—Alcohol increased the scores of the PCAG (sedation) Acute tolerance in TimeOut, SRT mean latency, drunkenness, scale compared with other conditions, partially counteracted by and driving capability was not observed (similar effects in the RB. In the T-C, it was also observed that A/RB produced greater ascending and descending limb of BAC). A strong association euphoric effects (ARCI-MBG), stimulant effects (ARCI-BG), and was found between BAC and driving capability in both alco- amphetamine-like effects (ARCI-A) than the other 3 conditions holic conditions whereas it was moderate with alcohol alone the first 2 hours. Interaction effects of RB with alcohol were for drunkenness, drowsiness, SRT mean latency, TT time out/ found in all previous subscales (AUC) whereas RB had no main number of errors, BAES-S, ARCI-A, and ARCI-PCAG (see Table 5). effects. Correlation turned weak when RB was present for most of them. Table 2. Subjective Effects Pharmacodynamics Parameters’ Statistical Analysis ES ES A A/RB RB P (95% CI) (95% CI) Outcomes Mean ± SD Mean ± SD MEAN ± SD Mean ± SD Parameter Alcohol RB Interaction A vs A/RB Drunkenness 51.81 ± 25.37 40.31 ± 24.72 0.00 ± 0.00 3.81 ± 8.14 Peak 48 (33.8 to 62.2)*** −3.8 (−18.0 to 10.4) N.S. N.S. mm 132.72 ± 83.27 105.14 ± 84.83 0.00 ± 0.00 4.75 ± 10.30 AUC0-8h 127.9 (83.1 to 172.8)*** −4.8 (−49.6 to 40.1) N.S. N.S. Drowsiness 50.25 ± 28.79 25.31 ± 26.86 6.94 ± 21.74 12.25 ± 20.07 Peak 38.0 (23.6 to 52.4)*** −5.3 (−19.7 to 9.1) N.S. * ** mm 170.63 ± 131.86 56.97 ± 81.69 19.36 ± 69.22 36.67 ± 80.36 AUC0-8h 134.0 (92.2 to 175.7)*** −17.3 (−59.1 to 24.4) N.S. ** *** Dizziness 23.63 ± 24.72 15.63 ± 18.59 5.19 ± 18.96 4.31 ± 15.46 Peak 19.3 (8.5 to 30.1)*** 0.9 (−9.9 to 11.7) N.S. N.S mm 70.47 ± 101.31 33.02 ± 49.57 7.41 ± 28.71 6.44 ± 23.81 AUC0-8h 64.0 (28.6 to 99.4)*** 1 (−34.5 to 36.4) N.S. N.S Palpitations 3.69 ± 8.93 4.13 ± 8.92 5.75 ± 20.41 1.19 ± 4.75 Peak 2.5 (−4.2 to 9.2) N.S. 4.6 (−2.2 to 11.3) N.S. N.S. mm 15.83 ± 50.17 11.78 ± 28.12 9.38 ± 35.01 4.69 ± 18.75 AUC0-8h 11.1 (−1.8 to 24.1) N.S. 4.7 (−8.3 to 17.6) N.S. N.S. Anxiety 9.13 ± 17.24 5.31 ± 9.39 6.69 ± 22.35 2.94 ± 9.62 Peak 6.2 (−1.4 to 13.7) N.S. 3.8 (−3.8 to 11.3) N.S. N.S. mm 23.42 ± 62.26 13.70 ± 29.38 13.22 ± 48.53 9.00 ± 34.69 AUC0-8h 14.4 (−0.1 to 28.9) N.S. 4.3 (−10.3 to 18.7) N.S. N.S Headache 11.94 ± 17.60 5.00 ± 10.98 0.13 ± 0.50 3.13 ± 6.36 Peak 8.8 (0.8 to 16.9)* −3.0 (−11.1 to 5.0) N.S. N.S. mm 35.31 ± 63.71 9.13 ± 24.58 0.13 ± 0.50 6.98 ± 15.85 AUC0-8h 28.3 (1.3 to 55.4)* −6.8(−33.9 to 20.2) N.S. N.S. EAVc1 58.31 ± 25.73 41.00 ± 28.55 2.81 ± 11.25 3.69 ± 8.14 Peak 54.6 (39.5 to 39.5)*** −0.9 (−16.0 to 14.3) N.S. N.S. mm 148.72 ± 212.44 100.48 ± 76.08 5.59 ± 22.38 7.34 ± 16.36 AUC0-4h 141.4 (100.5 to 182.3)*** −1.8 (−42.7 to 39.2) N.S. N.S. mm 72.96 ± 96.31 85.41 ± 60.82 17.06 ± 48.26 19.16 ± 35.47 AUC0-8h 193.3 (135.1 to 251.4)*** −2.0 (−60.3 to 56.1) N.S. ** *** EAVc2 −61.94 ± 30.94 −41.56 ± 34.62 −3.00 ± 12.00 −5.81 ± 13.43 Peak −56.1 (−71.7 to −40.5)*** 2.8 (−128 to 18.4) N.S. N.S. mm −177.64 ± 116.40 −112.36 ± 103.41 −7.56 ± 30.25 −10.69 ± 24.31 AUC0-4h −167.0 (−220.7 to −113.2)*** 3.1 (−50.7 to 56.9) N.S. N.S. mm −247.09 ± 150.72 −107.28 ± 123.28 −21.13 ± 59.76 −24.47 ± 54.86 AUC0-8h −222.6 (−313.9 to −131.3)*** 3.3 (−87.9 to 94.6) N.S. * ** EAVc3 −69.50 ± 31.16 −50.44 ± 37.42 −2.19 ± 8.75 −6.38 ± 13.81 Peak −63.1 (−80.7 to −45.6)*** 4.2 (−13.4 to 21.7) N.S. N.S. mm −204.81 ± 121.55 −139.78 ± 118.95 −4.73 ± 18.94 −11.61 ± 27.05 AUC0-4h −193.2 (−253.6 to −132.8)*** 6.8 (−53.5 to 67.3) N.S. N.S. mm −284.00 ± 139.82 −127.84 ± 146.47 −13.84 ± 39.16 −23.81 ± 44.10 AUC0-8h −260.2 (−361.6 to −158.8)*** 9.9 (−91.4 to 111.4) N.S. * ** EAVc4 −78.50 ± 28.00 −60.13 ± 35.50 −1.56 ± 6.25 −7.81 ± 17.78 Peak −70.7 (−88.4 to −52.9)*** 6.3 (−11.5 to 24.0) N.S. N.S. mm −234.06 ± 105.57 −175.38 ± 116.47 −5.06 ± 20.25 −16.38 ± 40.12 AUC0-4h −217.7 (−276.4 to −159.1)*** 11.3 (−47.3 to 70.0) N.S. N.S. mm −334.69 ± 143.12 −166.91 ± 168.22 −13.25 ± 37.48 −34.56 ± 69.77 AUC0-8h −300.1 (−411.6 to −188.7)*** 21.3 (−90.1 to 132.8) N.S. * ** BAES-A 14.75 ± 9.07 22.69 ± 15.87 8.75 ± 11.47 3.13 ± 7.07 Peak 11.6 (4.2 to 19.1)** 5.6 (−1.8 to 13.1) N.S. N.S. score 37.73 ± 32.98 60.34 ± 49.64 18.68 ± 28.53 7.81 ± 25.59 AUC0-8h 29.9 (11.7 to 48.2)** 10.9 (−7.4 to 29.1) N.S. N.S. BAES-S 21.19 ± 13.83 12.63 ± 11.84 3.63 ± 12.68 5.63 ± 14.01 Peak 15.6 (9.2 to 21.9)*** −2.0 (−8.4 to 4.4) N.S. N.S. score 83.23 ± 81.40 44.27 ± 61.83 20.56 ± 77.85 26.33 ± 78.28 AUC0-8h 56.9 (32.5 to 81.3)*** −5.7 (−30.2 to 18.7) N.S. * ** ARCI-PCAG 4.81 ± 3.75 1.75 ± 3.92 −0.63 ± 2.87 0.94 ± 2.70 Peak 3.9 (1.7 to 6.0)*** −1.6 (−3.7 to 0.6) N.S. N.S. score 25.03 ± 21.73 6.22 ± 15.81 −0.53 ± 14.62 5.19 ± 11.24 AUC 0-8h 19.8 (10.6 to 29.1)*** −5.7 (−15.0 to 3.5) N.S. * *** ARCI-MBG 5.41 ± 8.97 5.19 ± 4.05 1.00 ± 1.32 0.75 ± 1.53 Peak 4.7 (0.7 to 8.6)* 0.3 (−3.7 to 4.2) N.S. N.S. score 5.20 ± 5.77 14.50 ± 12.69 3.09 ± 4.21 1.23 ± 4.57 AUC0-8h 4.0 (−1.4 to 9.3) N.S. 1.9 (−3.5 to 7.2) N.S * ** ARCI-LSD 1.38 ± 2.55 0.81 ± 2.43 0.44 ± 2.03 0.25 ± 2.08 Peak 1.1 (0.1 to 2.1)* 0.2 (−0.8 to 1.2) N.S. N.S. score 4.00 ± 13.42 3.69 ± 11.67 3.13 ± 13.04 2.14 ± 11.90 AUC0-8h 1.9 (−1.1 to 4.8) N.S. 1.0 (−2.0 to 3.9) N.S N.S ARCI-BG −1.25 ± 2.32 1.88 ± 2.16 0.81 ± 0.91 0.25 ± 1.61 Peak −1.5 (−2.9 to −0.1)* 0.6 (−0.9 to 2.0) N.S ** *** score −6.64 ± 8.74 5.59 ± 7.36 2.14 ± 4.76 −0.38 ± 3.71 AUC0-8h −6.3 (−11.0 to −1.5)** 2.5 (−2.3 to 7.3) N.S ** *** ARCI-A 1.93 ± 1.57 3.69 ± 2.12 1.00 ± 1.41 0.88 ± 1.59 Peak 1.0 (−0.1 to 2.2) N.S. 0.1 (.1.0 to 1.2) N.S. * ** score 6.56 ± 6.93 13.52 ± 9.84 3.97 ± 6.95 3.14 ± 7.90 AUC0-8h 3.4 (−0.8 to 7.6) N.S 0.8 (−3.4 to 5.1) N.S * ** Abbreviations: A, alcohol + placebo Red Bull; A/RB, alcohol + Red Bull; ARCI, Addiction Research Center Inventory; ARCI-A, amphetamine; ARCI-LSD, lysergic acid dyethylamide scale; ARCI-MG, benzedrine group, ARCI-MBG, morphine-benzedrine group; ARCI-PCAG, pentobarbital- chlorpromazine-alcohol group; AUC, area under the curve; BAES-A, Biphasic alcohol effects scale activation, BAES-S, biphasic alcohol effects scale sedation; CI, confidence interval; EAVc1, driving capability; EAVc2, willingness to drive an ill child to hospital; EAVc3, willingness to drive a sick friend home; EAVc4, willingness to drive a friend to a party; ES, estimated substance effect; RB, Red Bull + placebo alcohol; P, placebo alcohol + placebo Red Bull. N.S. mean not significant; * P < .05; ** P < .01; *** P < .001. Pérez-Mañá et al. | 19 20 | International Journal of Neuropsychopharmacology, 2022 Figure 2. Time course of subjective effects (differences to baseline). Data points and error bars represent mean and SD values for 16 participants. Conditions: alcohol (60 g); alcohol (60 g) + RB (240 mg caffeine), RB (240 mg caffeine), placebo. *P < .05 and **P < .01 indicate alcohol significant differences with alcohol + RB. Filled symbols indicate a significant difference from placebo (P < .05). The significance is only reported for the comparison of more interest (A vs A/RB) and between all conditions and placebo. Other comparisons are not included in the figure to make it easy to understand. Discussion Additionally, higher caffeine and alcohol concentrations were found with A/RB. In this study, alcohol impaired performance whereas EDs had The reduction in the time outside the road with the tracking no main or interaction effects with alcohol on driving-related test was 20% 2 hours after administration when RB was com- skills. Although ED co-treatment did not fully reverse or antag- bined with alcohol compared with alcohol alone (absolute differ- onize the effects of alcohol, for many tasks, performance after ence of 3.58 s). Other studies administering alcohol and caffeine the combination was significantly better than performance for showed mixed results. Caffeine capsules (2.93–5.87 mg/kg) par- alcohol alone at several time points. tially offset alcohol-induced impairment measured with the EDs increased perceived capability to drive and willing- CTT (Moskowitz and Burns, 1981) whereas no effect was found ness to drive under certain circumstances. Furthermore, EDs for decaffeinated coffee fortified with 200, 250, or 500 mg of caf- reduced alcohol-induced sedation and increased stimulation feine (Nuotto et al., 1982). In another study using a Bimanual at several time points but not unmask drunkenness feelings. Visuomotor Task, coffee did not counteract alcohol-induced Pérez-Mañá et al. | 21 Table 3. Alcohol and Caffeine Pharmacokinetic Parameters and Statistical Analysis for Comparison Between Conditions with Ethanol (A/RB vs A) and Conditions with Caffeine (A/RB vs RB) Values Outcome Parameters A/RB Alcohol P Alcohol plasma Cmax (µmol/mL) 18.2 ± 3.7 15.3 ± 2.2 ** tmax (h) 2.0 (1.5–2.5) 1.8 (1.5–2.5) N.S. AUC0-8h (µmol.h/mL) 64.1 ± 17.1 54.6 ± 17.6 ** Elimination rate (µmol/mL/h) 2.6 ± 0.7 2.7 ± 0.7 N.S. A/RB RB P Caffeine plasma Cmax (nmol/mL) 20.4 ± 2.9 17.6 ± 3.4 * tmax (h) 2.0 (1.5–6.0) 2.0 (1.5–4.0) N.S. AUC0-8h (nmol.h/mL) 111.9 ± 21.8 90.3 ± 20.2 ** t1/2 (h) 5.8 ± 2.8 5.4 ± 2.3 N.S. Caffeineu Excretion 0–8h (nmol) 32449.7 ± 10012.5 21568.6 ± 7262.1 ** Paraxanthineu Excretion 0–8h (nmol) 22531.8 ± 11004.6 40048.8 ± 16722.5 ** Theobromineu Excretion 0–8h (nmol) 13734.4 ± 4436.5 10785.3 ± 5123.6 N.S. Theophyllineu Excretion 0–8h (nmol) 405.0 ± 237.0 1460.2 ± 1587.0 * 17X/137X ratiou Excretion 0–4h 0.3 ± 0.1 0.9 ± 0.6 *** 17X/137X ratiou Excretion 4–8h 4.2 ± 2.3 6.4 ± 3.5 *** 17X/137X ratiou Excretion 0–8h 0.7 ± 0.4 2.0 ± 1.0 *** Abbreviations: Alcohol, alcohol + placebo RB; A/RB, alcohol + Red Bull; AUC, area under the curve; Cmax, peak concentration; P, placebo alcohol + placebo RB; RB, Red Bull + placebo alcohol; tmax, time to reach peak concentrations; t1/2, half-life; U, urine; 17X/137X, paraxanthine/caffeine ratio. Values are mean ± SD except for tmax (median, minimum and maximum). Paired Student’s t test: N.S. mean not significant; * P < .05; ** P < .01; *** P < .001. Amount of 18.2 µmol/mL of alcohol corresponds to 83.5 mg/ dL and 15.3 µmol/mL to 70.5 mg/dL. Figure 3. Time course of plasma concentrations of alcohol and caffeine. Data points and error bars represent mean and SD values for 16 participants. Amount of ­alcohol of 10 μmol/mL corresponds to 46.07 mg/dL and 20 μmol/mL to 92.1 mg/dL. Conditions: alcohol (60 g); alcohol (60 g) + RB (240 mg caffeine), RB (240 mg caffeine), placebo. *P < .05 and **P < .01 indicate significant differences among both conditions. (BAC 0.6 g/L) errors (Buela-Casal and Caballo, 1990). On the other of 31.3 ms). In most studies where caffeine/EDs were mixed with hand, EDs reduced dose dependently alcohol impairment in the alcohol, no improvement was found (McKetin et al., 2015) with CTT in the descending limb of alcohol concentrations (Peacock the exception of another trial conducted in a similar setting et al., 2015). Our results are in agreement with those observed (Azcona et al.,1995). Alford and colleagues (Alford et al., 2012) with simulated driving with caffeinated beer (383 mg of caffeine also showed a trend (P < .1) with an ED to compensate the in- and 1 g/kg of alcohol), where the medium driving performance crease in recognition reaction time produced by alcohol (par- (speed, lane position, and crashes) did not improve compared ticipants received 2 alcohol doses to achieve 0.046 and 0.087% with non-caffeinated beer (Howland et al., 2011). However, also BrAC). With more potent psychostimulants, whereas cocaine with simulated driving, 200–400 mg of caffeine counteracted reduced the alcohol-induced increase of SRT (Farré et al., 1993), alcohol (0.6 g/kg)-induced increases in braking latency (Liguori MDMA tended to produce more impairment (Hernández-López and Robinson, 2001). The correlation between performance in a et al., 2002). tracking task and SD of lateral position measured with a driving Results in the NB task were congruent with a study where no simulator exists but is modest (Verster and Roth, 2012); there- significant differences were found between control and alcohol fore, discrepancies between studies might easily exist due to groups (BAC of 0.02 and 0.08%) in response accuracy or reaction the variability in the measurement instruments. The doses ad- time (Gundersen et al., 2008). Another study (n = 32), however, ministered and previous tolerance to effects must also be taken showed an increase in omission and commission errors with into account. heavy memory load (2-back) (Casbon et al., 2003). In the case of A reduction of 12% in mean latency of SRT task was found movement estimation, we did not find a reduction of the impair- with A/RB at 2 hours compared with alcohol (absolute difference ment produced by alcohol when RB was added. Similar results 22 | International Journal of Neuropsychopharmacology, 2022 Table 4. Vital Signs Pharmacodynamics Parameters’ Statistical Analysis ES ES A A/RB RB P (95% CI) (95% CI) Inter- Outcomes Mean ± SD Mean ± SD Mean ± SD Mean ± SD Parameter Alcohol RB action SBP 5.06 ± 16.61 9.25 ± 13.69 7.50 ± 11.56 −0.56 ± 11.57 Peak 5.6 (−3.1 to 14.4) N.S. 8.1(−0.7 to 16.8) N.S. N.S. mmHg −8.94 ± 46.98 16.53 ± 50.70 18.20 ± 44.57 −8.13 ± 36.83 AUC0-8h −0.8 (29.0 to 27.3) N.S. 26.3 (−1.8 to 54.5) N.S. N.S. DBP −6.31 ± 12.86 −0.75 ± 14.72 7.13 ± 9.18 −1.00 ± 10.66 Peak −5.3 (−12.8 to 2.2) N.S. 8.1 (0.6 to 15.6)* N.S. mmHg −36.72 ± 48.46 −13.05 ± 51.88 17.42 ± 33.75 −14.92 ± 35.84 AUC0-8h −21.8 (−48.1 to 4.6) N.S. 32.3 (6.0 to 58.7)* N.S. Heart rate 15.06 ± 11.13 11.75 ± 12.21 0.38 ± 10.51 4.38 ± 13.51 Peak 10.7 (3.1 to 18.3)** −4.0 (−11.6 to 3.6) N.S. N.S. bpm 58.34 ± 45.45 53.13 ± 63.88 −6.58 ± 37.09 6.48 ± 52.05 AUC0-8h 51.9 (17.5 to 86.2)** −13.1 (−47.5 to 21.3) N.S. N.S. Temperature −0.34 ± 0.49 0.03 ± 0.64 0.02 ± 0.72 −0.33 ± 0.55 Peak −0.0 (−0.4 to 0.4) N.S. 0.4 (−0.0 to 0.7) N.S. N.S. ºC −0.83 ± 1.66 0.51 ± 1.99 0.88 ± 2.56 −0.84 ± 2.15 AUC0-8h 0.0 (−1.4 to 1.5) N.S. 1.7 (0.3 to 3.2)* N.S. Abbreviations: A, alcohol + placebo Red Bull; A/RB, alcohol + Red Bull; AUC, area under the curve; CI, confidence interval; DBP, diastolic blood pressure; ES, estimated substance effect; P, placebo alcohol + placebo Red Bull; RB, Red Bull+ placebo alcohol; SBP, systolic blood pressure. N.S, not significant, * P < .05; ** P < .01; *** P < .001. Table 5. Correlations Between Alcohol Concentrations and Effects. Data are Expressed as r (95% CI) BAC Outcomes A A/RB Drunkenness 0.58 (0.45 to 0.68) 0.64 (0.53 to 0.73) Drowsiness 0.61 (0.50 to 0.70) 0.26 (0.10 to 0.40) Dizziness 0.44 (0.30 to 0.56) 0.37 (0.22 to 0.50) EAVc1 0.75 (0.62 to 0.84) 0.70 (0.55 to 0.80) SRT mean latency 0.50 (0.25 to 0.69) 0.13 (−0.16 to 0.40) TT time out 0.54 (0.30 to 0.72) 0.20 (−0.09 to 0.46) TT errors 0.53 (0.29 to 0.71) 0.38 (0.11 to 0.60) BAES-A 0.29 (0.13 to 0.43) 0.52 (0.39 to 0.63) BAES-S 0.63 (0.52 to 0.72) 0.38 (0.23 to 0.51) ARCI-A 0.55 (0.35 to 0.70) 0.72 (0.57 to 0.82) ARCI-BG −0.33 (−0.54 to −0.03) 0.48 (0.27 to 0.65) ARCI-LSD 0.18 (−0.07 to 0,41) 0.27 (0.02 to 0.48) ARCI-MBG 0.41 (0.18 to 0.60) 0.61 (0.42 to 0.74) ARCI-PCAG 0.64 (0.47 to 0.77) −0.04 (−0.29 to −0.21) BrAC 0.96 (0.94 to 0.97) 0.96 (0.93 to 0.97) Abbreviations: A, alcohol + placebo Red Bull; A/RB, alcohol + Red Bull; ARCI, Addiction Research Center Inventory; ARCI-A, amphetamine; ARCI-LSD, lysergic acid dyethylamide scale; ARCI-MG, benzedrine group, ARCI-MBG, morphine-benzedrine group; ARCI-PCAG, pentobarbital-chlorpromazine-alcohol group; BAES-A, Bi- phasic alcohol effects scale activation, BAES-S, biphasic alcohol effects scale sedation; BAC, blood alcohol concentrations; CI, confidence interval; BrAC, breath alcohol concentrarions; RB, Red Bull + placebo alcohol; EAVc1, driving capability; SRT, simple reaction time; TT, tracking test. were found in 30 volunteers using another test of movement (Ferreira et al., 2006; McKetin et al., 2015). The consumption of estimation and a coffee (Buela-Casal and Caballo, 1990). EDs allows subjects to stay awake for longer on a party night and In summary, our results on driving related-skills suggest that could lead to faster (Marczkinski et al., 2017) and possibly higher driving would improve when EDs are mixed with alcohol com- alcohol consumption than expected. pared with alcohol alone. However, to better assess the real im- Interestingly it was observed that A/RB consumption pro- pact, a driving simulator should be used. duces more pleasant effects than alcohol alone (more euphoria In relation with perceived impairment, A/RB improved the and amphetamine-like effects in ARCI), although maximum subjective driving capability measured with VAS at several time scores were mild in comparison other psychostimulants (Farré points. Most studies have not shown an effect of EDs/caffeine et al., 1993; Hernández-López et al., 2002). It has been pro- in these outcomes (McKetin et al., 2015). Discrepancies could be posed that caffeine antagonizes unwanted effects of alcohol explained by a reduced acute tolerance in our subjects. through changes in adenosine neurotransmission. Caffeine In our study, perceived intoxication (drunkenness feelings) is an adenosine receptor antagonist more effective when ad- was similar with A/RB when compared to alcohol alone. Other enosine activity is high and the individual is feeling sleepy studies also did not demonstrate a clear reduction in drunken- or sedated, both circumstances produced by alcohol ingestion ness (Benson et al., 2014; Verster et al., 2018), even with more (Ferré et al., 2011). In addition, caffeine enhances the reward potent psychostimulants (Farré et al., 1993; Hernández-López experienced from alcohol because it reduces adenosine ef- et al., 2002). A possible explanation is that drunkenness refers to fects on dopamine neurotransmission (activation of A2A re- negative behavior and physical effects of alcohol and only some ceptors inhibits dopamine transmission) and contributes to symptoms can improve with psychostimulants. the continued alcohol consumption (Marczinski, 2014). These Furthermore, a reduction in drowsiness/sedation produced results are in the same line of studies in rats (Roldán et al., by alcohol was observed with A/RB, as in previous studies 2018). Furthermore, taurine also increases dopamine levels Pérez-Mañá et al. | 23 in nucleus accumbens (Ericson et al., 2006). Altogether these night. Furthermore we used the most consumed brand of ED data suggest that co-administration of both drinks could in- (RB), but results may not extrapolate to all of them. crease the risk of development of alcohol use disorders, an The sample size was small. Power calculation was based hypothesis that should be tested in future studies. on the primary endpoint and may not have allowed to find dif- The pharmacodynamic changes do not seem to be explained ferences in some secondary endpoints (e.g., NB). Furthermore, due to kinetic mechanisms as both alcohol and caffeine con- women were not included so the results cannot be extrapo- centrations increased with A/RB. Regarding pharmacokinetics, lated to them. We enrolled only males for avoiding potential an inhibition of caffeine elimination by alcohol was previously sex differences in ethanol pharmacokinetics and subjective reported (Mitchell et al., 1983). Alcohol intake significantly pro- effects, mainly due to a lower volume of distribution, reduced longed the caffeine half-life and diminished the caffeine clear- metabolism and a decreased tolerability to ethanol in women ance (George et al., 1986), and the AUC for caffeine was also (Mumenthaler et al., 1999; Baraona et al., 2001). significantly higher when caffeine was administered with 0.8 g/ In our study a tracking task similar to the one used to ob- kg of alcohol (Azcona et al., 1995). Authors proposed that al- tain the driving license in Spain was used. Although the test cohol inhibition of caffeine metabolism could be related with has not been validated to assess the effects of acute alcohol alterations in membrane function, NADPH levels or inhibition consumption, a dose-response effect has been found with of drug binding to cytochromes (Mitchell et al., 1983; George our own data (after the first administration the effects were et al., 1986). In our study caffeine half-life did not increase but it lower than after the second one). Otherwise, the results in was calculated with data only till 8-h. the tracking task were congruent with those obtained in SRT. Our results in urine showed less paraxanthine concentra- Future studies should be conducted to confirm our results tions with A/RB, in comparison with RB, supporting caffeine using a driving simulator, including women and testing dif- metabolism inhibition through CYP1A2 by alcohol (Gazzaz ferent doses of alcohol and EDs. et al., 2018). The increase in alcohol concentrations with the mix however, was not expected. Most studies have found Conclusions no differences (McKetin et al., 2015) or just the opposite one (Peacock et al., 2015), and also with other psychostimulants This interaction study shows that alcohol impairs driving- (Farré et al., 1993; Hernández-López et al., 2002). Increases ob- related skills; the addition of EDs reduced, but did not eliminate, served in our study were mild in magnitude but found in 14 the effects of alcohol at several times and in several tasks. The volunteers. Cmax also was higher with A/RB, so it seems that reduction of the alcohol-induced sedation using EDs could favor a component in RB increased alcohol absorption. Both mixers the use of alcohol for longer periods of time and an underesti- (Red Bull and Seven-Up) have natural sweeteners, gas, and mation of alcohol-induced impairment. At the pharmacokinetic nearly the same carbohydrate and energy content, so these level, alcohol mixed with EDs increased modestly caffeine and components also do not seem to play a role. Caffeine also does alcohol concentrations. Mechanisms involved should be further not affect gastric myoelectrical activity or gastric emptying investigated. (Boekema et al., 1999; Jonderko et al., 2014). Nevertheless, ef- fects on alcohol absorption of other differential ingredients Supplementary Materials could not be discounted (Huang et al., 2011). Additionally, a Supplementary data are available at International Journal of small fraction of alcohol could be using a common metabolic Neuropsychopharmacology (IJNPPY) online. pathway with caffeine, such as CYP1A2 (Salmela et al., 1998). Regardless of the explanation, consumption of both beverages in less-tolerant individuals could favor higher intoxication Acknowledgments levels. Future studies should include different ED brands (or We want to thank Esther Menoyo, Soraya Martín, Yan Zhang, compositions) and study separately the effects of each ingre- Dídac Prat and Mohammed Ezzel Din their contribution in the dient on alcohol pharmacokinetics. conduct of the study, Jordi Serna for his contribution in bio- Blood pressure was higher with A/RB than with alcohol at logical samples analysis. Laura Blanco-Hinojo and Dídac Macià several time points. These differences can be explained by caf- contributed with driving tests programming. feine peripheral vasoconstriction effects (Fletcher et al., 2017). This work was supported by a grant from Ministerio del Additionally, both alcoholic conditions increased heart rate, ex- Interior, Dirección General de Tráfico-DGT (SPSIP2015-01798), Red plained by sympathetic nervous system activation with alcohol de Trastornos Adictivos-RTA (SPIP2015-01798), Red de Trastornos (Spaak et al., 2010). Both increases are modest but should be Adictivos-RTA (RD16/0017/0010), Plan Nacional Sobre Drogas (PNSD taken into account in subjects with previous cardiovascular dis- 2018I037). Clara Pérez-Mañá and Esther Papaseit benefited from eases like arterial hypertension or arrhythmias. In fact, reported Juan Rodés fellowships (ISCIII, JR15/00005 and JR16/00020, respect- cases of atrial fibrillation after EDs consumption in healthy par- ively). The author’s work was independent from sources of funding. ticipants suggest that EDs can be arrhythmogenic (Di Rocco et al., 2011). Furthermore, a greater volume of urine was gen- erated with A/RB because alcohol and caffeine have both diur- Statement of Interest etic properties, increasing the risk of dehydration (Stookey, 1999; None. O’Brien et al., 2008). The main strength of our study is the complete factorial interaction design. Furthermore, the cross-over design allows References each subject to be its own control avoiding bias due to variability Alford C, Hamilton-Morris J, Verster JC (2012) The effects of en- in previous alcohol and caffeine tolerance. Moreover, the study ergy drink in combination with alcohol on performance and was double-blind to reduce observer and participant expectancy subjective awareness. Psychopharmacology 222:519–532. effects. 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