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Breast Cancer Drugs Are Hiding in Bodybuilding Supplements

Researchers found a medicine called tamoxifen in a dietary supplement.
Image: Okka Pykkö/Flickr

On the one hand, substances marketed as dietary supplements can be full of random crap that does very little beyond playing Russian roulette with any allergies you might have. On the other hand, they can also be full of prescription drugs that certainly shouldn’t be for sale in the unregulated “supplements” aisle.

In a letter published in the British Medical Journal last night, a team of European researchers wrote that they had discovered one such medicine in an off-the-shelf bodybuilding supplement: tamoxifen, an “anti-oestrogen” drug usually prescribed to treat breast cancer or female infertility.


Why might such a drug be present in a supplement aimed at gym rats? Because it’s also prescribed off-label to treat gynaecomastia, a condition where men grow enlarged breast tissue. Also known by the delightful slang terms of “gyno” or “bitch tits,” it’s a common side-effect of taking anabolic steroids. A 2012 report on “human enhancement drugs” explains that steroid users often take tamoxifen to prevent gynaecomastia, though it’s traditionally been sourced from the illicit market.

In this new work, researchers from the European Monitoring Centre for Drugs and Drug Addiction and Liverpool John Moores found tamoxifen in a dietary supplement called Esto Suppress. Simon Brandt, one of the authors of the letter, explained in an email that they were first alerted to the situation by discussions on bodybuilding forums. “The reason for this speculation came from the chemical name that was written on the label which pointed in that direction,” he said. “This particular product was also widely available from a number of online retailers and while some indications existed [where] the same chemical name was mentioned, others were seen to list a modified version of that name which did not always make much chemical sense.”

He characterised this case as “hiding in plain sight,” given that the drug was actually listed on the label—albeit in quantities that didn’t match up to the real values. And, you know, the name “Esto Suppress” kind of gives away the whole oestrogen-blocking effects. In a Google search, the first site I found selling the supplement described it: “Esto Suppress eliminates estrogen from your system and is essential post cycle, or on-cycle, when using any heavily aromatizable compounds.” Aromatization is the process of converting testosterone to oestrogen—and can be caused by steroids.


The researchers purchased four bottles of the supplement between 2011 and 2012, and tested them for tamoxifen. Three of them contained the drug in varying doses, and the fourth didn’t. Brandt sent me pictures of three of the capsules, which you can see are all a slightly different shade—“One of those things that should not happen either given that you would expect the products to be identical,” he said. They can’t say if Esto Suppress on sale today contains tamoxifen.

Three Esto Suppress capsules tested by the researchers, all with slightly different shading. Image: Simon Brandt

The problem with supplements containing drugs like this, aside from the fact that you probably don’t know what you’re taking or how much, is that these substances are regulated for a reason; they can be powerful drugs. Brandt explained that tamoxifen doesn’t even have a license to treat gynaecomastia; a prescriber has to make a clinical judgment.

Esto Suppress is far from the first supplement to be caught containing a pharmaceutical product. In their letter, the researchers explained that since the 2000s they’ve found “supplements” with ingredients including “anabolic steroids, erectogenics, stimulants, appetite suppressants, and anxiolytic,” and added, “Some of these substances have been withdrawn from use in medicines owing to safety concerns, others have never been tested in humans.”

They recommend that doctors ask patients about supplements they might take and report adverse reactions. In the UK, the Yellow Card scheme invites healthcare professionals and the public to report side effects to any kind of drug or supplement.

But tackling the problem means going further back, according to Brandt. He suggested that we need to find out who is using “enhancement” products, why, and what the risks are, as well as addressing difficulties caused by different regulatory systems around the world and improving awareness of new findings like this one.