Some nutritional supplements marketed for muscle building contained contaminants. (Steve Debenport/Getty Images/iStock)

Researchers found unapproved and sometimes dangerous drugs in 746 dietary supplements, almost all of them marketed for sexual enhancement, weight loss or muscle growth, a new analysis published Friday shows.

The review of a Food and Drug Administration database of contaminated supplements for the years 2007 to 2016 most commonly turned up sildenafil — the drug sold as Viagra — and other erectile dysfunction drugs in sex enhancement products; sibutramine and the laxative phenolphthalein, both banned by the FDA, in weight-loss supplements; and steroids or their analogues in muscle-building products.

About 80 percent of the supplements were contaminated by one pharmaceutical that should not have been in the product. Twenty percent contained at least two such drugs, and two of the supplements contained six unapproved drugs. One product contained a drug that raises blood pressure and another drug that lowers it. Despite these contaminants, fewer than half the products were recalled.

The presence of unknown drugs in supplements “poses a serious public health risk,” the researchers wrote. More than 50 percent of the U.S. population consumes dietary supplements, and many consumers mistakenly believe the products are carefully regulated and accurately labeled.

The drugs found in the supplements have “the potential to cause serious adverse health effects owing to accidental misuse, overuse or interaction with other medications, underlying health conditions or other pharmaceuticals,” the researchers wrote.

Controversy over adulterated supplements stretches back decades. Under a 1994 law, the Dietary Supplement Health and Education Act, the products are regulated as food and therefore not subject to premarket safety and effectiveness testing imposed on pharmaceuticals. The $35 billion supplement market includes multivitamins, minerals, botanicals and other products.

The new paper, written by a team from the California Department of Public Health, was published online Friday in JAMA Network Open.

In an interview, Daniel Fabricant, president of the Natural Products Association, a supplement industry trade group, said it is unfair to consider sex enhancement, weight-loss and muscle building products in the same category as traditional dietary supplements such as vitamins. He said these are fringe products, often made by fly-by-night manufacturers and sold on the Internet or in convenience stores.

“We’re completely on the FDA’s side here,” said Fabricant, who worked at the federal agency regulating supplements earlier this decade. “This is someone spiking the product. They’re saying it’s a supplement. It’s not a supplement in any way, shape or form.”

Fabricant said his organization supports the FDA using its authority to bring misdemeanor charges against companies that adulterate supplements with drugs.

But Pieter Cohen, who wrote an editorial that accompanied the new study, said many tainted supplements come from well-known manufacturers based in the United States. He cited a 2014 study that he and others conducted that found 20 of 27 supplements were still adulterated with drugs and available for purchase between eight and 52 months after they were recalled by the FDA.

In his editorial, Cohen, an associate professor at Harvard Medical School who conducts research into the safety of dietary supplements, called on the FDA to more aggressively act against companies that produce adulterated supplements and urged an overhaul of the 1994 law. He suggested that companies be required to register the products with the FDA before sale.

In a statement issued late Friday afternoon, an FDA spokesman said the FDA was analyzing the study’s findings.

“The FDA is committed to doing everything within its resources and authorities to identify and remove unsafe products from the market” and “to help ensure that products marketed as dietary supplements are safe, well-manufactured, and accurately labeled.”

The spokesman, Jeremy Kahn, said that when the FDA takes action against one distributor, others may still market the product, and that supplements are sometimes relabeled to evade detection.

The new analysis of the FDA’s Tainted Products Marketed as Dietary Supplements database contained some alarming findings about the three types of products. For example, the prescription antidepressant fluoxetine, or Prozac, was found in about 5 percent of the weight-loss products. Sibutramine, widely found in the weight-loss products, can substantially increase blood pressure and pulse rate. The FDA withdrew it from the market in 2010 because of its potential to cause strokes.

The active ingredients in Viagra, Cialis and Levitra — widely found in the sex enhancement supplements — can interact with nitrates found in medicine prescribed for diabetes, high blood pressure and high cholesterol and can dangerously lower blood pressure, the researchers said.

Men precluded from taking erectile dysfunction drugs may turn to these supplements, not realizing that they are getting the very same pharmaceuticals, they said. Others may choose them because they are less expensive or because they are readily available at gas stations and convenience stores, Cohen said.

“As the dietary supplement industry continues to grow in the United States, it is essential to further address this significant public health issue,” the researchers wrote.