Melatonin

While the authors are limited by the one page format of the article, I see a danger in oversimplifying readers' understanding of this all too readily available drug, especially since the article does not address what happens when patients go beyond recommended doses. Two cases from the recent past to illustrate:

Patient one suffered from chronic insomnia, and in desperation, took large amounts of melatonin, thinking that if one pill was not enough to get her to sleep, then more would be better. When her menstrual cycles became disrupted, she ended up being over-investigated for menstrual irregularities. Having seen her after these investigations had begun, I pointed out to her that there was a time when melatonin was considered as a potential candidate for human contraception(1). When she discontinued the melatonin, her cycles were restored to baseline.

Patient two was using melatonin based on reports in the medical literature of its potential benefit for the treatment of cancer(2) . While aiming for a daily dose of 20 mg, he could only tolerate 9 mg before having to discontinue due to severe constipation. Multiple attempts at reinstating the regimen ended due to constipation, and the problem resolved each time the melatonin was discontinued. Eventually this therapeutic path was abandoned. I had never heard of melatonin causing constipation, and in reviewing the literature, I was made aware of close to four decades worth of research on gastrointestinal melatonin(3). The majority of the body's melatonin is in the gastrointestinal system, and its release is not triggered by light and darkness but by the food we eat. I strongly suspect that this patient's constipation was triggered by his melatonin use. To date, this side effect has not been described in the medical literature. I suspect that this side effect may be due to melatonin's ability to increase colonic transit time(4). I have been remiss until now in reporting this side effect (as are many of my colleagues when it comes to reporting adverse effects of supplements purchased at health food stores), so I thank the CMAJ for giving mean opportunity to help raise awareness of this potential side effect.

Melatonin is a fascinating chemical. Its sedative, analgesic, hypnotic, anticonvulsant, antioxidant, anti-inflammatory, immunomodulatory and chronobiotic properties raise hopes for numerous therapeutic possibilities. I hope that someday the CMAJ will do a more thorough literature review on the subject.

Harold Pupko M.D.

1)http://www.ncbi.nlm.nih.gov/pubmed/8365512

2) http://www.ncbi.nlm.nih.gov/pubmed/22271210

3) http://www.jpp.krakow.pl/journal/archive/08_08_s2/pdf/33_08_08_s2_article.pdf

4) http://www.ncbi.nlm.nih.gov/pubmed/1872000

Conflict of Interest:

None declared