- Consumption of drugs and/or herbal preparations capable of inducing hepatic enzyme metabolism (e.g., barbiturates, rifampicin, carbamazepine, phenytoin, primidone, or St. John's Wort) or enzyme-inhibiting agents (e.g., cimetidine) or similar drugs within 30 days (or 5 half-lives of inducing/inhibiting agent, whichever is longer) of enrollment in this study.