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Melatonin supplements are widely available at U.S. pharmacies and marketed as sleep aids for both adults and children.
While the hormone occurs naturally in the body, researchers argue that the supplement version is subject to far less oversight than its widespread use warrants, and that the consequences of misuse are underappreciated by the public.
In the U.S., the Food and Drug Administration (FDA) treats melatonin as a dietary supplement instead of a drug. Because of a 1994 law, supplements are regulated like food, so the FDA does not check their safety, effectiveness, or quality before they are sold.
The authority only steps in if there are reports of harm or false labeling. In countries like the U.K. and Australia, melatonin is considered a medication and is more strictly regulated.
Dr. Pieter Cohen, a researcher at the Harvard Medical School, found that the amount of melatonin in supplements can range from 74% to 347% of what the label claims.
Supplement labels do not have to include safety warnings or instructions, though many brands follow voluntary guidelines from the Council for Responsible Nutrition (CRN). These guidelines suggest adding disclaimers like "may cause drowsiness" and "for occasional or intermittent use only."
Beyond labeling concerns, researchers point to a lesser-known effect of melatonin: its role in regulating the circadian rhythm—the 24-hour internal clock that governs many bodily functions. When taken outside of a person's regular bedtime, melatonin can disrupt the body's sense of timing.
Supplement dosages typically range from 1 to 10 milligrams, while the body naturally produces the equivalent of roughly 0.3 milligrams per night, according to Margarita Dubocovich, a melatonin researcher at the University at Buffalo.
Taking melatonin at irregular times, such as during sleeplessness in the middle of the night, may induce symptoms similar to jet lag, including daytime drowsiness, irritability, upset stomach, and insomnia, Dubocovich said. She recommended taking a few milligrams at bedtime as the most effective and controlled approach.
Helen Burgess, who studies circadian rhythms at the University of Michigan, said that most people do not seem to realize how melatonin affects the body clock. She also said it is not a good idea to take more than 3 milligrams in the middle of the night, because the effects can last into the next morning.
Scientists are also worried about children using melatonin. Almost 1 in 5 school-aged children in the U.S. regularly take it to help them sleep, even though there is not enough long-term safety data for kids. As melatonin has become more popular, calls to poison control centers about children taking it have increased. Some cases have involved serious symptoms like breathing problems and seizures, although some of these effects may be due to serotonin found in certain products.
Cohen said that many parents think melatonin is harmless, comparing it to "a little glass of warm milk." However, he warned that giving children high doses or several doses can cause side effects and might not help them sleep.
Scientists are also looking at whether regular melatonin use affects puberty.
In some animals, melatonin helps control reproduction, and taking extra melatonin can disrupt this. The few studies in humans have not given clear answers, and researchers like Burgess say there are no long-term studies tracking hormone levels.
She is comfortable with children using melatonin for a short time now and then, but she advises parents to talk to a pediatrician if their child needs it regularly.
Some researchers believe that making melatonin an over-the-counter drug would force manufacturers to give accurate dosing information and clear instructions. Cohen said that people should be able to trust that the amount listed on the label is what they are actually getting.
Jeff Ventura, a spokesman for the CRN, said that if melatonin were moved into the drug category, it would need formal FDA approval. This could make it harder for people to get it, reduce the number of products available, and raise costs for both manufacturers and consumers.
Dubocovich, who has studied melatonin for 40 years, supports changing how it is regulated.
Burgess, who serves on the scientific advisory board for the melatonin brand Natrol, is not strongly opposed to its current availability because its effects are usually mild.
However, she recommends choosing well-known brands with a U.S. Pharmacopeia (USP) verification stamp, which indicates that the listed ingredients are accurate.
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