About 34 million Americans reach for the sleep remedy melatonin each year, spending a reported $378 million in 2014—lured by its reputation as an effective and natural sleep aid. But melatonin may not be as simple and safe a cure as many people hope.

Melatonin is in fact a hormone secreted by the brain’s pineal gland. It sets the body’s circadian rhythm, the 24-hour “clock” that helps control when you fall asleep and wake up. Traces can be found in barley, olives, rice, tomatoes, and walnuts, which is why the Food and Drug Administration allows a synthetic version to be sold over the counter. (In the U.K. you can get melatonin only through a doctor.)

Melatonin can ease sleep problems caused by shift work or jet lag. But overall, people taking the drugs fall asleep only 7 minutes faster and sleep 8 minutes longer on average, according to a 2013 analysis in the journal PLoS One.

The supplements pose some risks, too. About 20 percent of users in our survey reported next-day grogginess. And the Council for Responsible Nutrition, a supplement trade group, says to use caution before driving the next day.

Melatonin can also undermine blood pressure and diabetes medications. What’s more, “supplements aren’t regulated carefully, so what’s on the label may not be what’s in the pill,” says Marvin M. Lipman, M.D., Consumer Reports’ chief medical adviser.

If you want to try it, look for products with the “USP Verified” mark, which have been vetted by the nonprofit U.S. Pharmacopeia. And stick with low doses, too. Research suggests that 1 to 3 milligrams is enough for most people, and as little as 0.1 to 0.3 milligrams may be effective for some.

Editor's Note: This article also appeared in the February 2016 issue of Consumer Reports magazine.

These materials were made possible by a grant from the state Attorney General Consumer and Prescriber Education Grant Program, which is funded by a multistate settlement of consumer fraud claims regarding the marketing of the prescription drug Neurontin (gabapentin).