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The Explainer: Why clenbuterol?

A reader wants to know why an unethical athlete would look to clenbuterol for performance-enhancement.

Editor’s note: This Explainer originally was published in October. Stay tuned for more Explanations re: the Contador case.

Dear Explainer,
Thanks for the excellent article regarding Alberto Contador’s positive tests for clenbuterol and plasticizers.

The one thing that I haven’t heard questioned or explained yet, though, relates to why Contador would have had a trace of clenbuterol in his system in the first place? Let’s toss out the “tainted meat” theory for now. It’s also obvious that he didn’t have a Therapeutic Use Exemption for an inhaler that contained clenbuterol. The new plasticizer test would seem to imply that he received a transfusion and the added blood had traces of the drug. But why would the transfused blood show traces of clenbuterol? I assume he would have drawn that blood during training so as not to affect his racing. I also assume that if he doesn’t use clenbuterol during racing then there would be no reason to use it during training when it would provide no performance enhancing benefit and you could still risk getting caught with an out of competition test. Did he eat tainted meat during training, draw that blood and then transfuse it back during the Tour? What gives?
London, Ontario

Dear Mark,
The reason it might appear in an athlete’s system is essentially the same reason it might appear in meat sold by less-than-ethical producers. That reason is because the “off-label” use of clenbuterol goes beyond the drug’s qualities as a bronchodilator.

Why clenbuterol?
Lean and mean, but can Bessie climb?

Clenbuterol was, indeed, developed as an asthma treatment. The drug is similar to salbutamol, the asthma drug whose overuse resulted in the one-year suspension of Alessandro Petacchi. Like salbutamol, clenbuterol is a Beta2 adrenergic agonist, which relaxes those smooth muscle groups over which you exercise no direct conscious control. Salbutamol, for example, was often used to relax uterine muscles when a pregnant woman experiences premature labor, although a similar drug, terbutaline, is more commonly prescribed for that purpose. The relaxation of smooth muscle tissue would also result in the dilation of bronchial passages, hence the use of Beta2s as asthma drugs.

But under the World Anti-Doping Code, clenbuterol is banned entirely. Unlike salbutamol, there is no Therapeutic Use Exemption (TUE) available for clenbuterol. Asthma suffering athletes – and there seem to be a lot in cycling, if you review the number of TUEs issued – have to rely on salbutamol. Both were designed for similar purposes and both have the potential for abuse, so why the disparate treatment of the two drugs?

It’s that “potential for abuse” that goes to the core of the question. Beta2 adrenergic agonist drugs have been found to have certain “thermogenic” qualities. In layman’s terms, they tend to speed up a user’s metabolism. That increase in the Basal Metabolic Rate means that the body uses energy, even at rest. If you spend any time looking through cheesy weight-loss ads on the Internet, you’re bound to run across sites touting clenbuterol as an effective “FAT BURNER!!!!

Indeed, there have even been cases in which purportedly “natural” weight-loss and other supplements, like those containing the much-vaunted Acai Berry, have been contaminated (either intentionally or through sloppy production methods) with stimulants like oxilofrine, ephedrine and clenbuterol and steroids like nandrolone. There have been several law suits by athletes who’ve tested positive and claimed such contamination. Of course, that opens up another one of my big pet peeves, the complete lack of regulation of the supplement industry. (We can generally thank Utah Senator Orrin Hatch for blocking those efforts, but alas, I digress.)

While detailed studies of clenbuterol’s qualities as a “FAT BURNER!!!!” are pretty limited, there is some data and a lot of anecdotal evidence to suggest that it might, in fact, be true. Indeed, it is that characteristic that led meat producers to try clenbuterol on cattle and pigs in an effort to boost the ratio of muscle tissue to fat. Theoretically, it should produce a leaner cut of meat. Whether that is actually the case is really irrelevant, because the simple fact that some unethical producers believed it to be true prompted them to try it. There have been cases in which meat tainted by rather large doses of clenbuterol have made it to market and have triggered symptoms of an overdose (nausea, vomiting, heart arrhythmias, etc.) among those who later consumed it.

As a result, the practice has been banned. In Europe, that ban came into effect in 1999. With a more cautious regulatory approach, the U.S. took another decade, but it’s now banned here, too. So, Contador’s argument is that even though there is a ban in effect, cattle producers – much like some unethical cyclists – may be ignoring the regulation if there is a real (or perceived) benefit. Recent sampling data from Spain, however, suggests that the practice is now either rare or non-existent. There have been no clenbuterol positives in Spanish beef since that country’s regulators instituted regular testing nearly three years ago. Contador has, as far as we know, not been able to produce a sample of similarly tainted beef.

It’s those same thermogenic qualities that might prompt an athlete to take the drug directly in the off-season. If a drug improves the muscle-to-fat ratio, it will directly affect that ever-so-critical number in cyclists’ minds, namely the strength-to-weight ratio. If it also happens to open up the bronchial system, well, so much the better. Logic would suggest that if those thermogenic qualities are really at play, off-season use would make sense. Train hard in the off-season, burn fat (even in your sleep) and hope that the guy holding a plastic beaker doesn’t show up at your door.

If the speculation is true – and again, the whole thing is speculative at this point – Contador could have withdrawn blood with trace amounts of clenbuterol on the assumption that his earlier use was no longer detectable. If it were the case that there were trace amounts in that stored blood, then it probably wouldn’t have been discovered under ordinary circumstances … except that the German lab in Cologne is really, really good at finding small levels of drugs (and plasticizers).

Remember that Contador tested positive for 50 picograms (a picogram is a trillionth of a gram) of clenbuterol per milliliter of urine. To put that in perspective, look back at the aforementioned Petacchi case. Petacchi had a TUE that allowed him to have levels of salbutamol of 1000 nanograms (a nanogram is a billionth of a gram) per milliliter of urine. He tested for 1352 ng/ml.

So, Mark, there really is a reason for an unethical athlete to look to clenbuterol for performance-enhancement. There is a sound explanation for why traces of the drug showed up in Alberto Contador’s urine. Contador says that sound explanation is that his beef dinner was tainted by a unethical cattle producer. Others suggest that the sound explanation involves an unethical cyclist.

I guess we’ll be watching from the sidelines to see which of those explanations proves to be the most sound of the two. Either way, as Ricky often told Lucy, “someone has a lotta ‘splainin’ to do.”

“The Explainer” is a regular feature on If you have a question related to the sport of cycling that our editors might be able to answer, feel free to send your query to and we’ll take a stab at answering. Not all letters will be published and some questions may be combined with those of other readers. Please include your full name and hometown.