French scientists recently have warned against the indiscriminate use of Melatonin. Despite the fact that Melatonin has been released for public use in the United States by the Food and Drug Administration and is available over the counter nation wide, there currently is a total lack of information on the side effects of Melatonin. In Europe, Melatonin has a completely different status in that it is considered a “neuro-hormone” and cannot be sold over the counter. Even though administration of Melatonin in humans and animals has not shown evidence of toxic effects (i.e. no death), a drug toxic file still would need to be prepared and approved by the regulatory authorities.
Several features that are specific to this neuro-hormone, need to be taken into consideration. Melatonin is secreted during the night; it is the hormone of darkness (it presents a circadian rhythm and circannual). The duration of these secretions also can have an impact on the reproductive system. An inappropriate time of Melatonin intake could induce superphysiological concentrations of this hormone. This could mean that a long duration of exposure to Melatonin may mimic an “artificial darkness” condition when circadian rhythms are distorted. Furthermore, administration of large doses of Melatonin could induce excessive concentrations of Melatonin and of different metabolites that could have deleterious effects. Numerous books, magazines and articles have praised Melatonin as a “miraculous cure-all” for ailments ranging from sleeplessness to aging without any clinical evidence of efficacy (with the exception of its resynchronizing effect).
Very little attention has been paid to the possible side effects of Melatonin. Nightmares, hypotension, sleep disorders, abdominal pain, etc, have been reported. In fact, analysis of the known pharmacological profile of Melatonin and/or of its metabolites, based on scientific preclinical studies, constitutes a basis for prediction of adverse drug reactions or side effects. These impacted areas include the central nervous system, cardiovascular system, blood, glucose metabolism, immunology, and cancer development.
The knowledge of the fundamental mechanism of action of Melatonin (including metabolites) remains unknown. There are two types of Melatonin receptors and the possibility of damaging the structure of neuro or endocrine cells cannot be excluded. Melatonin can effect peripheral cells particularly the suprachiasmatic nucleus that “drives” the circadian rhythm to many other areas on which it projects. Among those is the hypothalamus, which plays a fundamental role in hormonal homeostasis of the organism. Melatonin is not a candy but a drug and should be treated as such.
Source: Journal of Biological Rhythms.Dec.12(6),1997:697-706