Dietary supplements for weight loss, energy, sexual function or muscle building are popular among young people. But they led to 1,392 adverse event reports in people under 25 from 2004 to 2015, with more than 40 percent of them severe or even fatal.

A 1994 law prohibits the Food and Drug Administration from screening supplements for safety or efficacy, and requires only that manufacturers assert that their products are safe before selling them.

Using an F.D.A. database, researchers focused on 977 of the adverse events that occurred after taking a single supplement. Among them were 166 hospitalizations, 39 reports of life-threatening events and 22 deaths. Most adverse events were among 18- to 25-year-olds. The study is in the Journal of Adolescent Health.

Compared with vitamin supplements, weight loss supplements were 2.6 times as likely to cause a severe adverse event, muscle supplements 2.7 times as likely, sexual function aids 2.4 times as likely and energy enhancers 2.6 times as likely.

“Drugs are tested very carefully before launching,” said the lead author, Flora Or, a researcher at the Harvard T.H. Chan School of Public Health. “With supplements there is no such testing. And there is huge underreporting of these adverse events. Many physicians don’t report these things. What we’re really seeing is the tip of the iceberg.”