Safety of melatonin in long-term use (?)

There are no published long-term safety data on the use of melatonin for whatever purpose, assuming long term to mean more than 6 months of daily medication. In the light of its physiological role in animals, the potential deleterious effects include inhibition of reproductive function, delayed timing of puberty, and influence (when taken during pregnancy and lactation) on the circadian status of the fetus and neonate and on future development. Its interactions with other medications are virtually unexplored. For most positive effects published, there also exist negative reports. There are insufficient data on its use in organic or psychiatric disease for any evaluations to be made. There are insufficient data on dose, formulation, and consequent relationships of individual pharmacokinetics and pharmacodynamics for recommendations at present. However, in normal healthy adults over 18 years old, not pregnant or lactating, with no personal or family histories of psychiatric disorder, and unmedicated except for oral contraceptives and minor analgesics (if necessary), the only significant short-term side effect in the author's experience has been sleepiness following oral ingestion of synthetic melatonin (5 mg or less, oral fast release), licensed for human experimental use and for prescription on a named-patient basis.