The breast cancer drug tamoxifen had been found in samples of a widely available bodybuilding dietary supplement, according to researchers.
In a letter to the British Medical Journal they explain that for over 30 years bodybuilders have taken tamoxifen to prevent and treat gynaecomastia (breast swelling) caused by use of anabolic steroids.
Usually, tamoxifen is sourced from the illicit market, they say. However, bodybuilding discussion forums have speculated that a dietary supplement called Esto Suppress contains tamoxifen because the label listed one of its chemical names.
The researchers purchased four samples at different times between late 2011 and early 2012 and analysed their contents. Tamoxifen was found in three out of the four samples at different concentrations (3.8 mg, 0.9 mg and 3 mg). The product label suggested a dosage of two capsules a day, which in the case of sample 1 may have provided 7.6 mg of tamoxifen (10-20 mg is used clinically for treating gynaecomastia).
Since the 2000s a growing number of off-the-shelf "food," "herbal," or "dietary" "supplements" – aimed at gym goers and people wanting to lose weight or enhance their sex lives – have contained pharmacologically active substances.
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