S-Adenosyl methionine may well have an antidepressant action beyond a placebo effect but this is virtually confined to endogenous depression. This should be subjected to further study. Our own double-blind placebo-controlled study is still incomplete. The indications are that SAM specifically affects folate, dopamine, and serotonin metabolism as well as activating and switching brain mechanisms. This suggests exciting prospects for further investigations. SAM is a nontoxic physiological metabolite virtually free of side effects.