Melatonin is a hormone secreted by the pineal gland, which is located at the base of the brain.

What it does in the body

Melatonin functions as an internal biochemical clock and calendar. It has a wide range of physiological effects including modulation of the sleep-wake cycle; temperature; and cognitive, hormone, cardiovascular and immune systems. Melatonin also has antioxidant effects. The melatonin-generating system is light- sensitive, with highest levels of production occurring at night in darkness. Melatonin production declines with age.

MelatoninToxic effects

Some users have reported headache, nightmares, hypotension, sleep disorders and abdominal pain. Melatonin may also worsen the symptoms of depression. There have been no studies on the side effects of long-term use.

Therapeutic uses of supplements

Sleep disorders

Melatonin supplements may be useful in improving sleep duration and quality in those in whom the normal cycle is disrupted, such as in those with jet lag and shift workers. Melatonin levels also decrease with increasing age. Melatonin appears to promote sleep by correcting abnormalities in sleep-wake cycles and by exerting a direct soporific effect, especially when administered during the day. Melatonin supplements should be taken in the evening.

In a 1997 placebo-controlled, double-blind, cross-over study, researchers assessed the effects of melatonin in eight males. Following a 7-hour night-time sleep, the participants were given either a placebo or one of three doses of melatonin (1 mg, 10 mg, and 40 mg) at 10 am. All doses of melatonin significantly shortened the time taken to go to sleep. Melatonin also significantly increased total sleep time and decreased wake after sleep onset.

In another placebo-controlled study, researchers studied the effects of single evening doses of melatonin on sleep in 15 healthy middle-aged volunteers. Compared to placebo, the 1.0 mg dose of melatonin significantly increased sleep time, sleep efficiency, non-REM Sleep and REM sleep latency.

Jet lag

Melatonin use in jet lag appears to decrease jet lag symptoms and hasten the return to normal energy levels. In a double-blind placebo-controlled study published in 1993, New Zealand researchers investigated the efficacy of melatonin in alleviating jet lag in 52 flight crew members after a series of international flights. The optimal time for taking melatonin in this group was also investigated. The participants were randomly assigned to three groups: early melatonin (5 mg started three days prior to arrival until five days after return home); late melatonin (placebo for three days then 5 mg melatonin for five days); and placebo. The results showed that the late melatonin group reported significantly less jet lag and sleep disturbance following the flight, compared to placebo. The late melatonin group also showed a significantly faster recovery of energy and alertness than the early melatonin group, which reported a worse overall recovery than placebo.


Melatonin seems to affect the immune response to cancer, possibly via effects on cytokines, which inhibit the growth of tumors. In a 1998 study, researchers assessed the effect of melatonin therapy on 31 patients (19 males and 12 females) with advanced solid tumors who had either failed to respond to chemotherapy and radiotherapy or showed insignificant responses. The results showed that in 12 patients, there was no further growth of either the primary tumor or of secondaries. These patients also experienced an improvement in their general wellbeing.



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