Supplement contamination and anti-doping
Evidence: strong
Supplement contamination with undeclared banned substances is well documented, not a fringe worry. Anti-doping holds the athlete responsible for whatever is in their body, so the risk lands on the runner. Third-party batch certification is the sensible defence, but it lowers the risk rather than removing it.
Not medical advice
This is a general knowledge base, not medical or dietary advice. If you are weighing up a supplement or a change to your diet, speak to a doctor or registered dietitian who knows your situation, and, if you compete under anti-doping rules, check current guidance from your anti-doping body.
A supplement can be useless and harmless, or it can carry something that was never on the label and should never have been in the tub. Whether a product works is the subject of evaluating supplements and the marketing playbook; whether it is clean and safe is a separate question, and for anyone who competes under anti-doping rules it is sometimes the more important one.
Contamination is real and measurable
The landmark study is old but still the reference point. An IOC-funded analysis bought 634 non-hormonal supplements from suppliers across 13 countries and found that 94 of them, or 14.8%, contained anabolic-androgenic steroids, mainly undeclared prohormones, that were not listed on the label (Geyer et al. 2004). Roughly one in seven ordinary supplements, bought off the shelf, carried a banned substance nobody had disclosed.
Later work has widened the picture without softening it. A review of 23 studies analysing supplements for prohibited substances found contamination rates ranging from 12% to 58%, a spread that reflects how varied and often high-risk the sampled products were, so it should be read as a range across studies rather than a single figure for all supplements (Martínez-Sanz et al. 2017). The problem is not confined to steroids. Laboratory testing of sports and weight-loss supplements has repeatedly found undeclared prohibited stimulants, including several never approved for human use and some linked to serious harm; in one analysis of 17 brands, many held two, three or even four different banned stimulants that were not on the label (Cohen et al. 2021). The categories most often implicated are the predictable ones: muscle-building, weight-loss and pre-workout products making dramatic claims.
Strict liability puts the risk on you
Anti-doping runs on a principle called strict liability: an athlete is responsible for any prohibited substance found in their sample, regardless of how it got there or whether they meant to take it. ‘It was in my supplement’ is not, by itself, a defence. An athlete who can prove that a contaminated product was the source may receive a reduced sanction, but there is usually still a consequence (USADA guidance). The burden of proof, and the cost of getting it wrong in lost results, a ban or a damaged reputation, sit with the runner rather than the manufacturer.
Certification lowers the risk without removing it
The practical defence is third-party batch testing. Independent schemes such as Informed Sport and NSF Certified for Sport test supplements against a large panel of banned substances and certify the batches that pass, so choosing certified products markedly lowers the chance of a contaminated one. The anti-doping bodies are explicit that it lowers the risk rather than removing it (USADA guidance), because testing samples batches and cannot check every unit.
The sensible order of operations follows the food-first stance of the IOC consensus: meet your needs from food where you can, keep the number of supplements small, and use only those with a real evidence base. Where you do supplement, prefer batch-certified products, keep a record of what you took and when, and accept that the residual risk still rests with you. For most recreational runners, who are never tested, contamination is mainly a question of health and honesty; for anyone in the testing pool, it is a question of their career.