12. Taking any type of nutritional or herbal supplement, including melatonin, known to have a centrally-acting effect. However, participants who have been taking supplements such as Echinacea, chondroitin, or glucosamine may enter the study if a) they have been taking these agents for at least one month prior to the study, and b) they continue on these agents throughout the study. Supplement information will be presented at intake, and the cessation of any such supplements will be required for the participant to continue in screening.