Melatonin - Adverse Effects

Adverse Effects

Melatonin appears to cause very few side-effects in the short term, up to three months, when healthy people take it at low doses. A systematic review in 2006 looked specifically at efficacy and safety in two categories of melatonin usage: first, for sleep disturbances that are secondary to other diagnoses and, second, for sleep disorders such as jet lag and shift work that accompany sleep restriction.

The study concluded that There is no evidence that melatonin is effective in treating secondary sleep disorders or sleep disorders accompanying sleep restriction, such as jet lag and shiftwork disorder. There is evidence that melatonin is safe with short term use.

Melatonin should not be taken by children as it can lead to serious developmental effects in children under 13 years of age. A research team in Italy has found that melatonin increased the chances of some cancers including lymphoma in children under the age of 10 years old.

A similar analysis by the same team a year earlier on the efficacy and safety of exogenous melatonin in the management of primary sleep disorders found that: There is evidence to suggest that melatonin is safe with short-term use (3 months or less).

Unwanted effects in some people especially at high doses (~3 mg/day or more) may include headaches, nausea, next-day grogginess, irritability, hormone fluctuations, vivid dreams, nightmares, reduced blood flow and hypothermia.

While no large, long-term studies that might reveal side-effects have been conducted, there do exist case reports about patients having taken melatonin for months.

Melatonin can cause somnolence (drowsiness), and, therefore, caution should be shown when driving, operating machinery, etc.

In individuals with auto-immune disorders, there is conflicting evidence whether melatonin supplementation may either ameliorate or exacerbate symptoms due to immunomodulation.

Individuals experiencing orthostatic intolerance, a cardiovascular condition that results in reduced blood pressure and blood flow to the brain when a person stands, may experience a worsening of symptoms when taking melatonin supplements, a study at Penn State College of Medicine's Milton S. Hershey Medical Center suggests. Melatonin can exacerbate symptoms by reducing nerve activity in those experiencing the condition, the study found.

A research team in Italy has found that melatonin supplementation in the evening in perimenopausal women produces an improvement in thyroid function and gonadotropin levels, as well as restoring fertility and menstruation and preventing the depression associated with the menopause. One study reported that melatonin taken in the evening raised prolactin levels in six out of seven women. Melatonin has been found to lower FSH levels. Effects of the hormone on human reproduction remain unclear, although it was with some effect tried as a contraceptive in the 1990s.

Melatonin was thought to have a very low maternal toxicity in rats. Newer studies, though, have found that it is toxic to photoreceptor cells in rats' retinas and increases tumours in white mice.