- have used or intend to use over-the-counter or prescription medication within 7 days prior to dosing. Herbal supplements must be discontinued 28 days prior to the first dose of trial medication. At the discretion of the investigator a shorter drug free or discontinuation period may be acceptable depending on the precise drugs/supplements taken. As an exception, paracetamol or acetaminophen may be used at doses of up to 1 g/day