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(1) In the United States melatonin is just a dietary supplement, but in Europe its status varies from country to country and also over time. It is illegal in some European member states but tolerated or authorised as a drug or dietary product elsewhere. Melatonin, a hormone secreted by the pineal gland, has been on the front cover of magazines throughout the world for its claimed effects on ageing, cancer and many other health problems, opening up a vast potential market. (2) Only its use in jet lag, sleep disorders and advanced cancer has been tested clinically (albeit scantily). (3) Melatonin seems to alleviate jet lag symptoms, but that could be linked to its moderate hypnotic effect. (4) The use of melatonin to treat major insomnia cannot be envisaged until its long-term safety has been proven. With this proviso, and if efficacy is confirmed in sufficiently large comparative trials, melatonin could prove useful for treating major sleep disorders in some patients, especially blind people and those with severe neurological disabilities. (5) According to open trials conducted by a single team, melatonin, alone or combined with interleukin-2, could slightly lengthen the survival of patients with some advanced cancers, but even partial tumour remissions are rare. (6) All other "indications" are based on simplistic hypotheses or purely commercial considerations.

This report summarizes presentations made at a National Institute of Mental Health-sponsored workshop dealing with recurrent winter depression, or seasonal affective disorder (SAD), and with phototherapy as its treatment. Workshop participants reviewed major issues in the following areas: (1) diagnosis, clinical characteristics, and epidemiology of the disorder; (2) critical issues in phototherapy research; (3) biologic effects of light and mechanism of action of phototherapy; (4) biologic abnormalities in SAD; and (5) animal models and their applicability to the study of SAD. Most research evidence to date supports the efficacy of phototherapy in the treatment of SAD. However, considerable controversy remains concerning its mechanism of action and the underlying pathophysiology of the disorder. These and other unresolved issues are reviewed, and areas of consensus in the field are identified.