- Treatment with any prescription or non-prescription drugs (including vitamins, herbal and dietary supplements, as well as grapefruit-containing products) within 7 days or 5 half-lives prior to first dose of study medication and until the end of the study. Treatment with any prescription drugs that are CYP2D6 inhibitors within 14 days prior to the first dose of study medication until the end of the study. Excluded from this list is acetaminophen at doses of ≤ 2 grams/day.