Melatonin is a hormone secreted mainly by the brain, whose main function is to provide information to the body relating to the day/night cycle, and to promote sleep.

In France, depending on the amount contained in a single (unit) dose, melatonin can be considered to have the status of either a drug or a food supplement. Irrespective of its dose and status, for sleep disorders melatonin is no more effective than a placebo in the short-term. Between 2009 and May 2017, the French National Agency for Food Safety (ANSES) registered 90 adverse effects linked to the consumption of food supplements containing melatonin. The French Health Products Agency (ANSM) recorded more than 200 adverse effects linked to the taking of melatonin, irrespective of its status, between 1985 and 2016.

The adverse effects reported were mainly neuropsychological disorders (fainting, drowsiness, headaches, convulsions, anxiety and depression), skin disorders including a range of rashes, and gastrointestinal problems (vomiting, constipation and damage to the pancreas). Cardiac rhythm disturbances, which regressed on stopping melatonin, were also observed.

A risk of interaction with numerous drugs is to be expected, with the potential to reduce their activity and/or to add to their adverse effects. Data on abnormalities observed in animals suggest that use of melatonin during pregnancy should be subject to the utmost caution.

In all situations, and irrespective of its status, melatonin is not a harmless substance. Its efficacy in promoting sleep is uncertain and it carries a risk of significant adverse effects.

©Prescrire 1 March 2019

"Melatonin: a review of adverse effects reported in France" Prescrire Int 2019; 28 (202): 72-73. (Pdf, subscribers only).

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