A new review of dietary supplements revealed that 746 of them were contaminated with unknown drugs. The vast majority of the supplements are meant for sexual enhancements, weight loss, and bodybuilding.

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Researchers at the California Department of Public Health combed through a Food and Drug Administration database of contaminated supplements for 2007 to 2016.

The findings suggest that about 80% of the dietary supplements were contaminated by one drug that should not have been in the product and 20% contained at least two such drugs. In the case of two particular supplements, researchers found six unapproved drugs.

The most common contaminants in supplements were sildenafil (Viagra) for sexual enhancement products; sibutramine and phenolphthalein in weight-loss products (both are banned by the FDA); and steroids in muscle-building supplements.

According to the study, more than half of the time, the FDA fails to enforce the recalls of supplements it has identified as containing unapproved drug ingredients.

Dietary supplements represent a $35 billion market, with more than 50% of the United States’ population consuming them.

Most supplement consumers wrongly believe that the products they are purchasing are regulated or vetted in some way. However, due to a 1994 law known as the Dietary Supplement Health and Education Act, such products are regulated as food. Therefore, they do not have to adhere to the strict rules or be subject to regulatory oversight like pharmaceuticals.

But — as this new study shows — many supplements contain pharmaceuticals. Worst of all, some products contain unlabeled pharmaceuticals. In light of this reality, the 1994 act ought to be overhauled. Many dietary supplements, such as vitamins, are risk-free, but the same can’t be said about the vast majority of sex, weight loss, and bodybuilding supplements — it is these categories that should be targeted for regulation.

“There’s many problems with the law [regulating supplements], so the ideal situation would be to revise the law so the FDA could do this much more efficiently,” Pieter Cohen, an assistant professor at Harvard Medical School who has studied the dangers of supplements, told Gizmodo. “One common-sense situation would be that individual brands need to be registered with the FDA prior to sale. And if they were found to be adulterated, the FDA would withdraw the registration and make them illegal to sell.”

Meanwhile, the FDA said that it is aware of the study’s findings and is in the process of analyzing them.

“The FDA is committed to doing everything within its resources and authorities to identify and remove unsafe products from the market, and we continue to work collaboratively with all of our stakeholders to help ensure that products marketed as dietary supplements are safe, well-manufactured, and accurately labeled,” reads their public statement.

When the FDA finds a supplement product that contains potentially hazardous ingredients, such as undeclared active pharmaceuticals, the agency said it works to remove it from the market. The challenge lies in the fact that even after a recall, other distributors may continue to sell the adulterated or misbranded product. The FDA has also found that distributors often re-label products to evade detection.

“Despite these challenges, the FDA recognizes the seriousness of this problem and continues to act within its resources and authorities to address this problem as best it can,” a FDA spokesman said.

The new findings were reported in the journal JAMA Network Open.