乌鸦传媒

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British researchers have found tamoxifen in supplements used by bodybuilders -- an active ingredient that isn't clearly labeled on the bottle.

Three out of four bottles of , purchased at four different times in 2011 and 2012, contained various doses of the estrogen-blocking breast cancer drug.

Tamoxifen was found at doses of 3.8 mg, 3 mg, and 0.9 mg, , of the European Monitoring Center for Drugs and Addiction, and colleagues .

At the label's suggested dose of two capsules per day, the highest dose would have delivered 7.6 mg of tamoxifen. The usual clinical dose for gynecomastia is 10 to 20 mg.

And there were no references to tamoxifen on the bottle, which prevents users from knowing exactly what they're taking, the researchers said. Only tamoxifen's obscure chemical name -- (Z)-1-(p-dimethylaminoethoxyphenyl)-1,2-diphenyl-1-butene -- was included in the label information.

"Often the substances are not listed on the labeling, and products may be marketed as 'natural,' exploiting the belief that they are safer and healthier options," they wrote.

Bodybuilders have been using tamoxifen for more than 30 years to treat gynecomastia, a side effect of taking too much testosterone. Excess estrogen is produced as a byproduct of having too much testosterone.

乌鸦传媒 has also reported that in addition to tamoxifen and aromatase inhibitors, bodybuilders also seek out investigational compounds that are not yet available on any market, including ghrelin mimetics like GHRP-2 and GHRP-6.

These drugs and supplements that claim to contain them are widely available on the Internet, and typically dodge any type of regulation given loose restrictions on a largely unregulated supplement market in the U.S.