A hormone secreted by the pineal gland that may help regulate a person’s circadian (approximately 24-hour) rhythm, including the sleep-wake cycle. Darkness stimulates the production and release of melatonin, and light suppresses its activity. The normal circadian melatonin cycle can be disrupted by any number of factors, including too much light at night, too little light during the daytime, rapid travel across time zones, and shift work. Melatonin also appears to regulate other cycles, including the menstrual cycle in women. It appears to influence when menstruation begins, the frequency and duration of the menstrual cycle, and when menopause occurs.
Synthetic melatonin supplements have been used for sleep disorders and a number of other medical conditions. The condition for which melatonin use has the most scientific support is jet lag. Several randomized, controlled human trials have suggested that taking melatonin orally the day of travel (close to the preferred bedtime at the destination) and continued for several days, can reduce some of the symptoms of jet lag. Specifically, melatonin use appears to reduce the number of days needed to establish a normal sleep pattern, decreases the amount of time it takes to fall asleep, improves alertness, and reduces daytime fatigue.
There is also relatively good scientific evidence that melatonin can improve delayed sleep-phase syndrome (in which the individual goes to bed very late and wakes up very late), sleep disturbances in children with neuropsychiatric disorders, and insomnia in the elderly, and can enhance sleep in healthy individuals. One recent study published in the journal Sleep showed that taking melatonin 30 minutes before bedtime improved sleep efficiency (total sleep time divided by the scheduled time in bed) in experimental subjects whose bodies weren’t making melatonin at the time. Melatonin has been touted as a treatment for a host of other medical conditions based on limited scientific data.
Taking melatonin over the short term appears to be safe, but the long-term safety of taking melatonin supplements is unknown. Since the US Food and Drug Administration does not require supplement makers to test their products the way drugmakers must, there is no guarantee of their safety or effectiveness. Some people experience vivid dreams or nightmares while taking melatonin. Other commonly reported side effects include stomach cramps, dizziness, headache, irritability, and diminished libido (sex drive). Melatonin may interact with a number of prescription drugs, including fluoxetine (brand name Prozac) and other antidepressants, zolpidem (Ambien) and other sedative drugs, and certain blood pressure drugs.
People with Type 1 diabetes taking melatonin have experienced high blood glucose, and melatonin has also been shown to reduce glucose tolerance and insulin sensitivity. Individuals with diabetes taking melatonin should consult their diabetes care team to determine whether the dose of their diabetes drugs needs to be adjusted.