Supplement Quality: Does It Contain What the Label Says?

Where the real risk sits

Supplements in the United States are not reviewed for quality or safety before they are sold. The FDA does not do a premarket safety review, and no regulator mandates a quality check first¹. That sounds alarming, and for some product types it should be. But the problems are not spread evenly across the shelf. They cluster in a few categories, and knowing which ones lets you relax about most of what you buy and be strict about the rest.

The FDA keeps a database of supplements found to contain hidden drugs. An analysis of its warnings from 2007 through 2016 found 776 adulterated products from 146 companies. Most were sold for sexual enhancement (45.5%), weight loss (40.9%) or muscle building (11.9%), and 20.2% contained more than one unapproved ingredient². The usual hidden drugs were sildenafil in sexual products, sibutramine in weight-loss products (84.9% of the adulterated ones) and synthetic steroids or steroid-like compounds in muscle-building products (89.1%). Some products were caught again after a warning, and in 19 of 28 repeat cases they now held a new unapproved ingredient. In 2014–2016, 38.6% of the adulterated samples came from online purchases and 34.3% from international mail shipments².

An update covering 2007 through 2021 counted 1,068 unique adulterated products. Sexual enhancement and weight loss were still the most common categories, and one product could carry up to 5 drugs. Besides sibutramine, weight-loss products contained sibutramine analogues, phenolphthalein (withdrawn over cancer risk) and fluoxetine. The update found no new adulterated muscle-building products after 2017, after they had been common earlier³.

The harm is real. A US surveillance study estimated about 23,000 emergency department visits a year from supplement adverse events, with about 2,154 hospitalizations. Weight-loss products were involved in 25.5% of single-supplement visits and energy products in 10.0%, and together they caused 71.8% of the supplement events with palpitations, chest pain or a racing heart⁴. A 2025 meta-analysis of 22 studies of weight-loss "natural" products found a pooled median of 37.5% contained a synthetic drug, with sibutramine the most common⁵.

Categories this site will not link for purchase

Because of this pattern, supp.science gives no buy link for some categories at all. These include fat burner formulas (history of DNP, sibutramine and DMAA adulteration), libido support formulas, horny goat weed and catuaba (spiked with undeclared sildenafil or tadalafil analogues), testosterone booster formulas and laxogenin (unlisted or designer steroids), adrenal support formulas (undeclared thyroid and steroid hormones), nootropic blends (unapproved drugs), detox tea blends and wild yam (undeclared pharmaceuticals or hormones). The individual pages explain the reasons.

Sports and bodybuilding products

Products sold online as SARMs (selective androgen receptor modulators, unapproved drugs) show what happens with no oversight at all. Of 44 tested, only 52% contained a SARM, 39% contained a different unapproved drug, 9% had no active compound, and 25% held substances not on the label. Only 41% matched the labeled amount⁶.

Ordinary-looking sports supplements are a smaller but real problem for tested athletes. A review of 23 analytical studies found contamination rates with substances banned by the World Anti-Doping Agency of 12–58%, often prohormones or stimulants⁷. Another review put the share of samples testing positive for anabolic agents or other prohibited substances at 14–50%⁸. These figures come from targeted testing of higher-risk products, so they do not mean half of all sports supplements are contaminated. They do mean that if you are drug-tested, an uncertified product is a gamble with your career.

Heavy metals in protein powder

Protein powder gets a lot of attention for metals. A risk assessment built on earlier testing (a Consumer Reports analysis of 15 products, and another study where 40% of 133 products had elevated metal levels) modeled one and three servings a day. It found no increased health risk from arsenic, cadmium, mercury or lead (hazard index below 1), and all modeled adult blood lead levels stayed below the CDC guidance value. The highest values, close to the limit, were in "mass gain" powders, and the lowest were in whey⁹.

A 2025 study of 56 European plant-based protein powders found measurable lead and cadmium. At 30 g a day, no element exceeded reference limits. At 100 g a day, copper, magnesium, molybdenum and iron intakes went over reference levels for some groups¹⁰. A Hungarian test of 22 powders (whey, vegan and beef) found nothing above regulatory limits, though the authors called it a reassuring snapshot rather than a guarantee¹¹.

The fair reading: at normal servings, whey protein and plant powders like pea protein do not look like a meaningful metal risk in these studies. The risk grows with very large daily amounts, so if you use several scoops a day, a product tested for heavy metals is a sensible choice.

When the dose is not what the label says

Hidden drugs are one problem. The other is a product that simply contains the wrong amount of what it lists.

Melatonin. A test of 31 melatonin supplements found content ranging from 83% below to 478% above the label, and lot-to-lot differences within one product of up to 465%. More than 71% missed the label by over 10%, and 8 products contained serotonin¹². A later JAMA analysis of US melatonin gummies found the actual content differed from the label in most products, some holding several times the stated dose and one containing none¹³. This matters most for children, since gummies are the main source of pediatric melatonin overdose calls to poison centers.

CBD. In 202 US CBD products, 74% were off their labeled potency by at least 10%, 26% did not match the type claimed (full spectrum, broad spectrum or isolate), and heavy metals were detected 52 times across 44 products¹⁴. In 56 CBD gummy products, 70% were more than 10% off the label, 39% contained THC, and the dose varied from gummy to gummy in the same bottle¹⁵.

Herbs. A global review of DNA testing on 5,957 herbal products from 37 countries found 27% were adulterated: they held undeclared species, substitutes, fillers, or none of the labeled plant¹⁶. Rates varied widely by country. Traditional medicines bought online carry a separate risk: in one study, 20.7% of Ayurvedic products contained detectable lead, mercury or arsenic, all of those exceeded at least one daily intake standard, and 75% of them claimed Good Manufacturing Practices¹⁷.

Gummies in general. We found no published lab analysis of creatine gummies, so we cannot say how accurate they are. The known issue is arithmetic: most gummies hold 1–1.5 g each, so you need 3–5 to reach the 5 g studied dose. Powdered creatine monohydrate avoids the question.

The reassuring side

Not every test finds problems. When 10 fish oil products in Australia and New Zealand were analyzed by an accredited laboratory, all met or beat their label for omega-3 content (EPA plus DHA averaged 109% of the claim) and all met the recommended peroxide limit¹⁸. Mainstream, single-ingredient products from established makers usually contain roughly what they say. The trouble concentrates in the categories above.

What third-party certification does and does not tell you

Several independent organizations test supplements and let products that pass carry their seal. Well-known names include NSF Certified for Sport, USP Verified and Informed Sport. Each program has its own quality assurance process with different testing components, which makes them hard for consumers to compare¹. We did not find peer-reviewed work describing exactly what each seal covers, so check the program's own published scope. A consensus statement from the US Anti-Doping Agency, Major League Baseball and military health researchers set out best practices for these programs for athletes and service members¹.

Certification is still uncommon. In one survey of military and civilian stores, only 12% of products were certified by an independent agency, and the authors noted that certification does not ensure safety or effectiveness¹⁹. A seal tells you a product passed that program's testing. It does not tell you the ingredient works. A certified product with limited evidence is still a product with limited evidence.

Red flags on the label

• Proprietary blends. US law lets a company list a blend's total weight and its ingredients without the amount of each one²⁰. You cannot tell whether the ingredient you care about is present at a studied dose. In libido blends, for example, each herb usually sits at a fraction of the dose used in its trials.
• Drug-like promises. Fast weight loss, instant erections, steroid-like muscle gain, "legal" versions of banned drugs. A supplement that truly delivers a drug-like effect may contain a drug, which is the pattern in the FDA data².
• Imported or online-only products from unknown sellers. A large share of adulterated samples were found through online sampling and international mail².
• Research chemicals and "not for human consumption." SARM-type products often did not contain what they claimed⁶.
• Many stimulants or overlapping products. Taking several products with the same ingredients stacks doses and raises risk⁸.

A short checklist

1. Prefer single-ingredient products with the amount stated per serving.
2. Choose a product with a third-party seal when you are drug-tested, give it to a child, or take large daily amounts (protein, for example).
3. Skip sexual enhancement, weight-loss, muscle-building "hormone" products and nootropic blends entirely. The evidence for them is limited and the adulteration risk is documented.
4. Buy from established retailers, not unknown overseas sellers.
5. Prefer powder or capsules over gummies when dose accuracy matters.
6. Stop and see a doctor if a supplement causes palpitations, chest pain or other unexpected symptoms, and tell your doctor about every supplement you take, especially with heart disease or prescription drugs.

Bottom line

Most mainstream single-ingredient supplements, such as protein powder, creatine or fish oil from established brands, are reasonably reliable. The documented risk is concentrated in sexual enhancement, weight-loss, bodybuilding and hormone products, unregulated CBD and melatonin gummies, and herbal products bought online. Avoid the high-risk categories, read past proprietary blends, and use third-party certification where accuracy matters most.