The most serious side effect noted in studies with amprenavir has been a potentially serious rash, which occurs in up to 30% of those who use the drug. It typically occurs within one to three weeks of first starting the drug and, in the worst circumstances, can escalate to Stevens-Johnson syndrome (in roughly 1% of people). This syndrome often results in very painful swollen lesions all over the body and is occasionally life-threatening. Other side effects associated with amprenavir and reported in studies include nausea, vomiting, diarrhea, abdominal pain and tingling around the mouth (called oral paresthesia).