What’s in melatonin—and is it giving you nightmares?

As many as one in three U.S. adults aren’t getting the seven to eight hours of sleep they need. Whether it’s a bombardment of stressful headlines, endless scrolling on a blue-light screen, or working into (or through) the night, our circadian rhythms are easily thrown off by modern life.

To fall and stay asleep, over six million American adults are turning to melatonin supplements, sold over the counter at pharmacies and grocery stores across the country.

Many of these users report side effects like nightmares. What’s causing them? And what’s in the melatonin tablets, liquids, and sprays we’re taking? 

Melatonin and vivid dreams?

Usually, side effects of melatonin include drowsiness and headaches, but experiencing vivid dreams and nightmares is certainly not uncommon, says Dr. Suzie Bertisch, assistant professor of medicine at Harvard Medical School and clinical director of behavioral sleep medicine at Brigham and Women’s Hospital.

Dr. Kin Yuen, a sleep medicine specialist at the University of California San Francisco, says higher doses of melatonin make dreams (and nightmares) more vivid and make us more likely to remember them after waking. 

(How COVID-19 can affect your sleep.)

One theory is that because melatonin increases time spent in REM cycles (when we dream), nightmares have a higher chance of appearing. Taking melatonin to help sleep when you’re experiencing emotional distress also presents a conundrum: are resulting nightmares a product of the melatonin, or the distress that caused poor sleep in the first place?

Currently, the reason many melatonin users experience nightmares remains unconfirmed. However, the fact that melatonin is widely available and doesn’t require a prescription in the U.S. and Canada—though it’s regulated in Australia, New Zealand, and most of Europe—may hold a partial answer.

Unpredictable product

Because melatonin is sold as a supplement, like vitamins, and not a medication, its regulation is limited. As a result, the amount of melatonin in a supplement can vary wildly, and may contain dangerous contaminants.

A landmark study that looked at 31 different melatonin supplements found melatonin content often varied greatly from the listed amount. One supplement had 478 percent more melatonin than what was listed on the label, another supplement had 83 percent less.

(How our body clock rules our lives.)

Almost one in three supplements tested also contained significant levels of serotonin, which can act in opposition to the supplement’s intended effect. Serotonin is associated with wakefulness and inhibition of REM sleep.

Serotonin is also strictly regulated and cannot be purchased over the counter. If someone taking another medication like an SSRI antidepressant took serotonin-contaminated melatonin, it could lead to serotonin overdose. Researchers urged manufacturers to identify where the serotonin was being introduced to their product—the origin of these contaminations are still unknown.

Medical-grade melatonin can be prescribed by a doctor and may help patients take a more pure, predictable dose.

How to use melatonin safely

Because the contents of melatonin supplements vary, Bertisch says there’s little data on the real world use of melatonin supplements over time. She says it’s generally safe for short term use in adults, like for getting over jet lag.

But kids’ use of melatonin supplements concern both Bertisch and Yuen. Bertisch says many parents are administering melatonin to their kids, but data on how this active hormone affects minors is very limited, especially over time. One theory is that melatonin supplements could affect fertility, though again, research is minimal at this point.

Melatonin is secreted naturally in people of all ages to signal us to wind down for bed, so changing habits like limiting screen time at night could be safer and more helpful than taking melatonin supplements.

(What is sundowning?)

Between 2012 and 2021, reports to U.S. poison control centers of children ingesting melatonin increased 530 percent, and melatonin became the most frequently ingested substance among children in 2020. Over 4,000 of the reported ingestions led to hospitalizations.

In September, The American Academy of Sleep Medicine urged parents to beware of melatonin gummies and chewable tablets on the market that can be easily administered to kids. They said this could lead to a melatonin overdose, which can manifest as headaches, dizziness and irritability.

Experts agree parents should check with a doctor before administering melatonin to kids. Also, given the lack of research on extended use, be careful about using melatonin long term, even if you’re an adult.