Dietary supplements you take can be tainted by prescription drugs and dangerous hidden ingredients, according to a new study

Many over-the-counter dietary supplements-especially those used for sexual enhancement and weight loss-are tainted by undisclosed pharmaceutical ingredients. This is the major finding of a recent review published in the Journal of Clinical Pharmacology.

An evaluation of the Food and Drug Administration's Health Care Fraud Database identified 1,068 unique dietary supplements sold from 2007 through 2021 that contained active ingredients found in prescription drugs or found to be too dangerous for human use. Among the tainted supplements identified in my study, 54% were for the treatment of sexual dysfunction and 35% were for weight loss. Although many such products are withdrawn from the market after detection by the FDA, other tainted supplements may enter the market instead.

Why it matters

Dietary supplements are used by 58% of U.S. adults. According to recent surveys by the Council for Responsible Nutrition, American consumers have a moderate level of confidence in the quality and safety of dietary supplements. However, my research shows that this confidence is misplaced because many dietary supplement products contain off-label synthetic active ingredients.

So what are these hidden substances, and why do they matter?

Many tainted weight-loss supplements conceal the active ingredient sibutramine, which the FDA recommended be removed from the U.S. market in 2010 after studies showed it increased the risk of heart attacks and strokes. And phenolphthalein, which is also commonly found in weight loss supplement products in the FDA database, was removed from over-the-counter laxative products in 1999 when the FDA reclassified it as "not generally recognized as safe and effective." The FDA warning came after studies showed the ingredient could damage human DNA and increase the risk of cancer.

The study also found ingredients approved only for use in prescription drugs. These include sildenafil and tadalafil, which are used in FDA-approved erectile dysfunction drugs such as Viagra and cialis. Such unintentional use can be dangerous because the active ingredients in these drugs carry risks such as vision loss or priapism, or prolonged penile erections. The study also documented frequent cases in which more than one active ingredient in erectile dysfunction drugs were combined in a way that was never studied for safety.

Another reason why hidden active ingredients are problematic is the risk of serious drug interactions. When active ingredients in erectile dysfunction drugs are used with medications for high blood pressure or prostatitis, such as nitrates and alpha-1-blockers, a life-threatening drop in blood pressure can occur.

Similarly, two of the dietary supplements identified in my study contained flibanserin, the active ingredient in the prescription drug Addyi, which is used to treat female sexual dysfunction. Flibanserin is generally safe, but can greatly reduce blood pressure when taken with alcohol.

Pharmacists check for these types of drug interactions before releasing prescription drugs. However, if dietary supplements contain undisclosed ingredients, there is no way to prevent unwanted drug interactions.

What is still unknown

Manufacturers of dietary supplements do not provide the FDA with evidence of good manufacturing practices before they sell them in the United States, and these manufacturers may change their products without notice. The FDA must prove that a dietary supplement product is unsafe before taking action, but this is difficult to ensure when more than 29,000 dietary supplement products are sold in the United States.

FDA evaluations are time-consuming and expensive because they also seek to identify other problems with dietary supplements, such as the presence of heavy metals, bacteria or mold. In addition, the process of evaluating these supplements is severely underfunded. The FDA alerts consumers to recently discovered tainted supplements through its Fraudulent Health Products Database, while trying to remove these products from the market.

If the product you intend to use is on this list, decline it. However, if your product is not included in the database, it may mean that it has not yet been evaluated.

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