A new study has found that the contents of some melatonin supplements, a popular sleep aid, are dramatically different from what’s listed on the label.

The study found that not only do these products potentially contain far more or far less active ingredient than advertised, but some also contain the brain chemical serotonin. Excess consumption of both melatonin and serotonin has been linked to a number of side effects that can range from mild to life-threatening. 

The findings, published Wednesday in the Journal of Clinical Sleep Medicine, offer the latest proof of something supplement industry critics have long warned about: When it comes to this poorly regulated corner of modern medicine, consumers often don’t know what they’re buying.

Researchers from the University of Guleph in Ontario, Canada, tested 31 different melatonin supplements from 16 different brands. The products were all purchased from local groceries and drugstores, and included a range of formulations such as liquid drops, gel capsules and chewable tablets.

Here’s what they found:

  • The actual melatonin content of those products ranged from 83% less to 478% more than the amount advertised on the label, with most products (21 out of 31) failing to fall within 10% of the label claim.
  • Variability within individual products was also high; some products differed by as much as 465% in their melatonin content from one package to the next.
  • Chewable tablets were the most variable products. The worst contained six times as much melatonin as advertised. As the study authors point out, chewables are the form most likely to be taken by children.
  • Eight of the tested products also contained serotonin, a by-product of melatonin degradation that has its own medicinal effects and risks associated with overuse.

While the products tested were all purchased from Canadian stores, experts in the U.S. say that the study should raise concerns here as well.

"The findings herald what may also be true in OTC [over-the-counter] melatonin supplements in the United States," Madeline Grigg-Damberger, M.D., director of Pediatric Sleep Medicine at the University of New Mexico in Albuquerque, wrote in a commentary published with the new study. Grigg-Damberger called for a similar study to be conducted on products bought from U.S. stores.

In response to the findings, the Council For Responsible Nutrition, a supplements trade group, issued a statement saying the industry provides "safe and beneficial" products to millions of people every year, but calling on individual supplement makers to test their products before bringing them to market.

"CRN supports enforcement action against companies unwilling to follow dietary supplement regulations," said Duffy MacKay, the group's senior vice president for scientific and regulatory affairs. MacKay also suggested that consumers "look to buy from retailers or brands they know and trust."

What Is Melatonin?

Melatonin is a hormone that the body produces naturally, and that works to mediate the sleep cycle.

Evidence that melatonin supplements can treat sleep disorders is shaky, and over-the-counter melatonin has been banned for years in the United Kingdom, European Union, Japan, and Australia.

Even so, these products are witnessing a surge in popularity in the U.S., where sales increased by more than 500% between 2003 and 2014, and where melatonin is the second most popular natural product used by children.

Melatonin supplements come in a range of formulations, including flavored liquids, rapid-dissolve tablets and strips, traditional chewables, and capsules that contain a blend of vitamins, minerals and plant extracts.
 

What Should I Do if I'm Taking Melatonin?

When you purchase any melatonin product (or any other dietary supplement, for that matter), make sure to look for the “USP verified” label. This seal indicates that the product has been subject to voluntary testing and meets US Pharmacopeia Convention standards (meaning the product is accurately labeled and free of harmful substances).

But before going to the store, you should talk to your doctor. Tell him or her about any prescription medications you are taking, as some of them may interact with melatonin. And make sure there’s at least some evidence that this particular supplement works for your specific sleep condition. The American Academy of Sleep Medicine recommends strategically timed doses as a treatment for jet lag and shift-work disorders. But its updated guidelines suggest that the drug may not work for people suffering from insomina.

What Are the Risks of Using This Supplement?

Common side effects related to melatonin supplements include dizziness and nausea. These pills can also undermine the effectiveness of blood pressure drugs and diabetes medication.

Authors of the new study say that people with diabetes, pre-diabetes or women who are pregnant may be particularly vulnerable to excessive melatonin consumption.

But for most people, serotonin poses an even bigger risk. It's possible to overdose on very low levels of this chemical, the study's authors write. The condition is known as “serotonin syndrome,” and can range from mild (shivering and diarrhea) to severe (muscle rigidity, fever and seizures). Serotonin syndrome can be exacerbated by the analgesic tramadol, and by certain anti-depressants (known as selective serotonin reuptake inhibitors, or SSRIs). Left untreated, the condition can be fatal.