I am not much of a fan of dietary supplements and have to admit to confirmation bias; I collect studies that provide evidence for skepticism about how well they work.
So when a reader, Arya Afrashteh, sent this study, I gave it some attention.
The study: Dietary Supplements as Source of Unintentional Doping. , , and . Biomed Res Int. 2022; 2022: 8387271. Published online 2022 Apr 22. doi: 10.1155/2022/8387271
The rationale: Athletes are not supposed to take performance-enhancing drugs but they are permitted to take dietary supplements. Are these safe?
Method: A review of the literature on unapproved substances found in dietary supplements.
Results: 875 of 3132 supplements contained undeclared substances.
Conclusion: ~28% of the analyzed dietary supplements pose a potential risk of unintentional doping.
Comment: Between one-quarter and one-third of dietary supplements taken for performance enhancement contained unlabled substances that could test as unapproved drugs.
This is a result of the Dietary Supplement Health and Education Act of 1994 (DSHEA) that basically deregulated dietary supplements. It took supplements out from under the control of the FDA.
All the FDA can do is write warning letters, which it occasionally does.
But unless the FDA is checking, you cannot be sure that what is in the supplements is accurately reflected by their labels. Sports supplements, it seems, are prime examples of why this is a problem.