- Subject has taken over-the-counter (OTC) medication within 48 hours prior to each assessment visit. T This includes the use of vitamins and natural or herbal remedies e.g., St John's Wort. Subjects who have taken OTC medication may still be entered into the study if, in the opinion of the physician responsible, the medication will not interfere with the study procedures or compromise safety. The occasional use of paracetamol for pain relief (within its labelled dosage) is permitted but must not be taken within 48 hours of an Assessment Visit.