Homeopathic formulas are based on the theory that even when a remedy (homeopathic remedy) is diluted to the point where no molecules are left, the water will retain the "memory" of what it was once in contact with. Homeopaths assert that the therapeutic potency of a remedy can be increased by serial dilution of the drug, combined with succussion, or vigorous shaking. This dilution is often repeated such that there is no active molecule present in the solution.