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Contamination of nutrition supplements

In 2004, a study was conducted by Hans Geyer in Germany. They purchased 634 supplements and found that up to 14.8% were contaminated with doping substances. In some countries it was more than 20%. That is more than 1 in 4 or 5 supplements tested that could have resulted in a doping violation. Now, more than 15 years later one would expect that the situation has improved.

Some studies suggest that the increased awareness has indeed reduced the problem but a more recent review article shows that the problem still exists (1). Contamination is still prevalent, there are still many issues with quality control: supplements may not contain what it promises on the label. We discussed problems with CBD products in this blog, but there are other studies as well that show poor quality control of supplements (2). Of course, many supplements are manufactured to very high standards, but a significant percentage that are available for purchase, are not.

Many supplements are manufactured to very high standards, but a significant percentage that are available for purchase, are not.

Contamination of nutrition supplements with doping substances

It is now well known that supplements can be contaminated with doping substances and can result in adverse analytical findings and positive doping tests. Supplements may have been contaminated with small amounts of prohormones, hormones, stimulants or other compounds that are on the list of banned substances. This could happen when manufacturing equipment isn’t cleaned to the required standards and contains remnants of ingredients from a previous product. This is similar to what can happen in a factory that manufactures nut products, as well as other products like cereals and breads. If the machines aren’t cleaned correctly or if particles of dust permeate manufacturing areas, the breads or cereals can contain remnants or traces of the nuts, which can be potentially dangerous to those with nut allergies.

Sources of contamination

In most cases contamination will be inadvertently due to a failure to clean equipment properly, but there is also evidence that in some cases supplements have been adulterated to make them more effective.

Since 2002, products intentionally faked with high amounts of 'classic' anabolic steroids such as metandienone, stanozolol, boldenone, dehydrochloromethyl-testosterone, oxandrolone etc. have been detected on the nutritional supplement market. These anabolic steroids were not declared on the labels either. The sources of these anabolic steroids are probably Chinese pharmaceutical companies, which sell bulk material of anabolic steroids. In 2005 vitamin C, multivitamin and magnesium tablets were confiscated, which contained cross-contaminations of stanozolol and metandienone 1.

The available data indicates that between 40-70% of athletes use supplements, and that between 12-58% of supplements may contain prohibited substances. This clearly indicates that there is a considerable risk of accidental or inadvertent doping through using supplements.

Athletes are responsible for what they put in their bodies

Because athletes sign a code of conduct, they are responsible for what they take, even supplements ­that have insufficient quality control or labelling. Athletes are 100% responsible for what they put in their bodies. Unfortunately, current legislation does little to protect athletes and other consumers from insufficiently labeled, mislabeled, contaminated, or even unsafe ingredients in dietary supplements. Although regulations vary widely from country to country, food supplements are never subject to the standard of manufacture and quality control that is required of foods and drugs. Also, legislation regarding product claims is less strict. Many manufacturers make claims that have never been proven scientifically.

What can you do to reduce the risk?

With clever marketing techniques and numerous retail outlets, supplement sellers make their products attractive and easy to obtain by athletes who do not know anything about the source or purity of the ingredients. Thus, if an athlete decides that the benefits outweigh the risks of taking a supplement, a product from a large, respectable company is probably the best choice. Reputable brands of vitamins, minerals, and other common supplements manufactured by the major food and drug companies are normally manufactured to high standards and should be safe.

Contamination is especially a problem in some smaller and more exotic companies, especially those targeting the bodybuilding world. Companies that do not sell steroids and prohormones are less likely to have their products contaminated by those substances. There are several things athletes can do to minimise the risk of contamination, including using products that have been tested through a quality assurance program. We will discuss this in more detail elsewhere.


  1. Geyer H, Parr MK, Mareck U, Reinhart U, Schrader Y, Schänzer W. Analysis of non-hormonal nutritional supplements for anabolic-androgenic steroids - results of an international study. Int J Sports Med. 2004;25(2):124-129.

  2. Geyer H, Schanzer W, Thevis M. Anabolic agents: recent strategies for their detection and protection from inadvertent doping. Br J Sports Med 2014; 48(10):820-6.

  3. Jeukendrup AE, Gleeson M. Sport Nutrition: an introduction to energy production and performance. 3rd edition ed. Champaign IL: Human Kinetics 2018.


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