Melatonin is an important hormone regulating our sleep. It is produced in the pineal gland in our brain and can also be manufactured and sold as supplement in forms of pills and capsules. In European countries, melatonin supplements are available only with prescriptions, however, in U.S., oral supplements of melatonin are available over-the-counter. In U.S., melatonin supplement are usually taken in as pills or capsules to aid combating jet-lag and insomnia. According to the reports published by National Institute of Health (NIH) 1, 2, 1.3% (3.1 million) of U.S. adults regularly take melatonin as supplements and the rate of melatonin use has been doubled among adults from 2007 – 2012. For children below 18 years old, the percentage of use rose significantly from 0.1% in 2007 to 0.7% (419,000) of U.S. children in 2012. Therefore, there is an urgent need to understand the possible side effect of taking melatonin as a supplement.
A meta-analysis on the possible adverse events associated with using melatonin supplements was recently published3. This meta-analysis looked at 50 studies on people taking in melatonin under either healthy condition or various medical conditions and aimed to find out whether there are any clinically-significant side effects related to melatonin use. Out of which, 5 of them were on children, 7 on older adults and the rest are on adults. 26 of these studies reported that there were no adverse effect related to melatonin use. In the remaining studies, melatonin supplements were reported to cause the following adverse effects.
- Fatigue, unwanted sleepiness/sleeplessness
- Reduce physical performance
- Increase in serum prolactin (reproductive hormone) and, to a minority of men, reduce sperm concentration and motility
- Reduce gluocose tolerance and insulin sensitivity in postmenopausal women
- Interact with other prescription drugs, such as, nifedipine, an antihypertensive medication
Some of the above adverse effects are avoidable. For example, we can take melatonin supplements at night before resting to avoid unwanted sleepiness, sleeplessness and reduced physical performance. However, research showed that melatonin potentially reduces blood pressure and therefore, may off-set antihypertensive medication. Further research needs to be performed on how melatonin interact with antihypertensive and people taking this medication should take melatonin supplements with caution.
- Clarke et al., “Trends in the Use of Complementary Health Approaches Among Adults: United States, 2002 – 2012” National Health Statistic Reports.
- Black et al., “Use of Complementary Health Approaches Among Children Aged 4-17 Years in the United States: National Health Interview Survey, 2007-2012” National Health Statistic Reports.
- Foley and Steel. Adverse events associated with oral administration of melatonin: A critical systematic review of clinical evidence. Complementary therapies in Medicine 2019 42, 65-81