When buying a dietary supplement, you probably assume that what’s on the label is what’s in the pill. But this assumption doesn’t always hold up, says Pieter Cohen, a physician at Cambridge Health Alliance.

In March, Cohen published his 14th paper concerning dietary supplements that contained either prohibited or unlisted ingredients. This time, he and his colleagues analyzed 17 brands of sports and weight-loss supplements sold in the United States, and they detected nine prohibited stimulants in them. Almost half of the brands tested included more than one prohibited stimulant.

People often turn to dietary supplements with the belief that they’re safer or more “natural” than pharmaceuticals, but research by Cohen, an associate professor of medicine at Harvard Medical School, and the Food and Drug Administration’s own records show that this isn’t always the case.

A 2018 study in the journal JAMA found that between 2007 and 2016, the FDA had identified 746 dietary supplements adulterated with pharmaceuticals, such as steroids or erectile dysfunction drugs, yet voluntary recalls were issued for only 48 percent of them, and the majority of these tainted supplements remained on the market.

The problem of contaminated supplements continues in plain view, Cohen says, because the Dietary Supplement Health and Education Act of 1994, or DSHEA, was created with heavy input from the supplements industry and consumers who use their products. As a result, the measure is widely seen as tilting the scales in favor of providing consumer access to supplements rather that ensuring safety. It limits government interference in the huge and growing market.

In those goals, it has succeeded “in a phenomenal way,” Cohen says. What the law hasn’t done is keep dangerous ingredients out of the supplement supply, he and others say.

The FDA does intervene when it can under the law.

“In the past year, the FDA has taken action against products whose labeling claimed the products would treat or prevent hangovers, depression, and other mental health disorders,” FDA spokesperson Courtney Rhodes told The Washington Post in a written statement. “These products were marketed as dietary supplements but were actually unapproved new drugs and/or misbranded drugs.”

The majority of new dietary supplement ingredients are introduced to the market without any safety evaluation by the FDA because of “loopholes, vague language in the law, and lack of industry compliance,” wrote Cohen and Scott Bass, an attorney who helped craft DSHEA, in a 2019 New England Journal of Medicine perspective.

In her statement to The Post, Rhodes said that a legislative proposal included in both the FDA’s fiscal year 2020 and 2021 budget requests “would require all products marketed as ‘dietary supplements’ to be listed with the FDA and give the agency authority to act against noncompliant products and the manufacturers and/or distributors of such products.”

But right now, Rhodes wrote, “The FDA currently has no systematic way of knowing what dietary supplements are on the market, when new products are introduced, or what they contain,” and that is true even if the product contains ingredients the FDA had previously acted against.

The FDA doesn’t have the funding to police supplements, and “there is no systematic monitoring of safety and effectiveness,” says Peter Lurie, a former FDA official who is now executive director of the Center for Science in the Public Interest.

“The single biggest problem is that FDA doesn’t know what’s on the market,” Bass says. He calls himself “pro supplement,” and notes that he has represented the supplement industry in legal cases, but he teamed with Cohen to argue in favor of rules that would require companies to provide the FDA with basic information and safety data about the products they’re selling so that the agency can know and track which products are being sold.

The supplement industry has seen astronomical growth in recent years. According to the Nutrition Business Journal, the top supplement categories in 2020 were: multivitamins, sports nutrition powders, meal supplements/replacements, Vitamins K, H and other combos and pre/probiotics.

In 1994, the supplement market was worth about $5 billion. Now it’s roughly $50 billion, says Loren Israelsen, president of the United Natural Products Alliance, an international trade association representing natural health products companies, including those making dietary supplements. “You have 10 times growth over 20 years — that’s remarkable, but I can assure you the FDA budget did not increase by 10 times.”

He says his group, which worked for the passage of the DSHEA, has spent “decades” advocating for more funding for the FDA so it can do more supplement monitoring

“There aren’t enough cops on the beat,” he says, adding that dangerous products hurt the industry as a whole. “It is in our interest for consumers to trust our products and have good experiences with them.”

But there can be a financial incentive for companies to cut corners.

One ongoing problem is something called “economic adulteration,” where some manufacturers replace expensive ingredients with cheaper ones, Cohen says.

This swapping can take place in and during the manufacture of the raw ingredients, so that the people or company making the final product and selling it to you are unaware — because they don’t realize that the raw ingredients they’ve bought are impure, Cohen says.

“There are so many middle people, and much of the industry’s products comes from ingredients made overseas in China,” Cohen says. Israelsen confirmed that China is the main supplier of many supplement ingredients, estimating that “70 to 75 percent of dietary ingredients are sourced from China.”

“Economic adulteration is a persistent problem for all industries that sell higher value commodities,” Israelsen says. “It is also a violation of federal law under the Food, Drug and Cosmetic Act.”

He says the supplements industry has responded by providing lab testing protocols to identify substituted ingredients as well as by releasing industry guidance and bulletins of specific new cases of adulteration found by the FDA.

The American Botanical Council, an industry trade group, releases publications that include Botanical Adulterants Prevention Bulletins, Laboratory Guidance Documents and the Botanical Adulterants Monitor e-newsletter.

Also, little assurance exists that herbal supplements contain the plant parts that consumers expect.

“There’s nothing in the law to ensure how the plant is extracted or prepared,” Cohen says. He uses garlic as an example, where the fleshy bulb is the part of the plant that people seek for health purposes. “We spend most of our time getting the good part of the garlic off of the leafy stuff, but the law would permit someone to take all those scraps, grind them up into a pill or capsule and call it garlic supplements,” he says.

Israelsen counters that the FDA does inspect for “good manufacturing practices” compliance, even overseas, and third-party certifications are also available for consumers who want added assurance. “Major retailers are working together under the banner of the GRMA [Global Retailer and Manufacturer Alliance] to set audit and compliance standards,” he says.

Despite these efforts, the FDA continues to find adulterated products.

“Unfortunately, there are examples where the FDA has determined that an ingredient in products marketed as dietary supplements is not lawful, for various reasons, and yet we can still find products marketed with these ingredients,” Rhodes wrote in her statement.

People don’t recognize the enormous business interests behind the supplement industry. “It’s not moms and pops growing herbs in their backyards,” says Catherine Price, author of “Vitamania: How Vitamins Revolutionized the Way We Think About Food.”

“There’s so much distrust of pharmaceutical companies — we’re desperate for something that seems safe and effective and somehow natural,” Price says, but “companies making supplements aren’t required to test their products for safety or efficacy at all.”

Given all this, how can you find a reliable supplement? Here are a few tips from experts.

Check the FDA’s list first. In April 2019, the FDA launched the Dietary Supplement Ingredient Advisory List, a catalogue of products consumers should be aware of, because they contain items that may not be in compliance with FDA rules. Ingredients on the list have not necessarily been determined unsafe by the FDA, but the agency is taking steps to evaluate them.

Look for third-party certification. To guard against adulteration and mislabeling, Cohen advises his patients to choose products that have been certified by a third party. Don’t trust any certification, however. Cohen says that legitimate programs are “dwarfed by hundreds of third-party certifications that tell the consumer nothing.” These companies do a cursory review, or in some cases “it’s a scam — a flat-out pay to pretend to do a review.”

Seek products with certification by U.S. Pharmacopeia (USP), which Cohen calls “the gold standard.” NSF International is another certification Cohen considers trustworthy. Supplement companies pay USP and NSF to certify their products, while a company called ConsumerLab buys products off the shelves and independently tests them. Customers can pay a fee to join and get access to its test results.

Cohen says ConsumerLab’s testing is “great,” but he cautions that they can “also give a lot of non-evidence-based advice about the use of supplements,” so he advises getting information about supplements themselves elsewhere, such as the website of the National Institutes of Health’s Office of Dietary Supplements. The National Center for Complementary and Integrative Health also provides assessments of herbal supplements and other alternative products that consumers can look up.

Keep it simple. It’s better to pick supplements that contain just a single ingredient. “If it just lists the one ingredient, in our experience, it will be more likely to be safe than if it contains multiple components,” Cohen says. Likewise, he says, it’s better to look for supplements that list ingredients you can identify than ones that use proprietary blends that they don’t disclose.

Beware of inflated claims. If a product sounds too good to be true, it probably is, Cohen says. DSHEA allows supplement companies to make “structure/function” claims, that suggest, for instance, that the product “supports the immune system.” Cohen says you’re better off avoiding products that make such claims, especially if they seem to cross the line into suggesting that they can treat or prevent a medical condition. Under DSHEA, Lurie says, “it’s okay to say the product ‘builds strong bones.’ It’s not okay to say it ‘prevents osteoporosis.’ ” This year, the FDA sent warning letters to 10 supplement companies that were claiming their products could cure, treat, mitigate or prevent depression and other mental health disorders.

Buy from reputable sources. Cheap supplements sold on the Internet are more likely to have issues with unlabeled ingredients or impurities than ones sold in stores such as Costco or Whole Foods, which have a process for vetting supplement products, Israelsen says. Costco’s store-brand supplements, for instance, are USP certified.

Avoid these categories of supplements. Some supplements are more likely to be tainted than others. A 2018 analysis of FDA records showed that the products most commonly found to be contaminated with unapproved pharmaceutical ingredients were ones marketed for sexual enhancement, weight loss or muscle building. Be cautious, too, of supplements touted for fighting or preventing covid-19. The FDA has sent warning letters to companies selling such products.