Clenbuterol - Food for Thought?

Published 20 July 2011

Clenbuterol - Food for Thought?

As the 2011 Tour de France started at the beginning of July, public and press attention began to focus not only on the outcome of the race but also on the possibility that another cyclist may be found to have an adverse analytical finding on doping testing. Furthermore, an impending appeal to be heard by the Court of Arbitration for Sport (CAS) is attracting a wide audience as it involves Alberto Contador, the current holder of the Tour de France title and a three-time winner of the same race.

Contador is in the midst of a long-running doping saga which has been ongoing since July 2010 when he tested positive for the banned anabolic substance clenbuterol during the 2010 Tour de France. He claimed that it could have been in his body only through the ingestion of contaminated meat and that the meat consumed was a steak brought from Spain. The Spanish cycling federation RFEC (Real Federación Española de Ciclismo) appear to have accepted that there was “no fault or negligence” on Contador’s part for his positive doping test and decided not to ban him on 15 February 2011. However, both the UCI and WADA lodged appeals at the Court of Arbitration for Sport (CAS) in Switzerland against the decision of the RFEC and the hearing before the CAS is scheduled for 1-3 August 2011.

What is clenbuterol? 

Clenbuterol is a non-steroidal ?2-agonist drug which has found use in the treatment of asthma through its action as a bronchodilator. However, it can act as an anabolic agent, promoting muscle growth and fat depletion, leading to its unlawful use in sports training and farming. It is known that cardiac and muscular side effects can occur in humans when it is used above the therapeutic dose of 40-160 mcg/day. 

There is evidence from studies in mice that clenbuterol selectively builds certain skeletal muscles in preference to other muscle types. It has been established from studies that the dose used in the mice to produce a 15% increase in muscle weight over 10 days is thought to be equivalent to a dose of 70-100 mcg per day in humans. It is not uncommon to find websites which offer “advice” on using clenbuterol to increase muscle and “burn” fat suggesting a three week cycle of taking 20-80 mcg clenbuterol per day then a 2-3 week rest cycle, followed by repeating the process. 

WADA and the Prohibited List of substances 

Clenbuterol is on the World Anti-Doping Association (WADA) Prohibited List and is subject to in-competition and out-of-competition testing. As clenbuterol is an exogenous substance (one that does not occur naturally in human physiology and metabolism), the detection of any quantity of clenbuterol in an athlete’s sample is treated as an adverse analytical finding. As WADA has stated: “There is no threshold under which this substance [clenbuterol] is not prohibited”. 

Under anti-doping's laws of strict liability, an athlete is responsible for any prohibited substance found in their urine. This means any positive test (adverse analytical finding) will attract a 2 year ban for a first offence, if the athlete cannot provide an innocent explanation. 

Positive doping tests for clenbuterol 

However, Contador is not the only elite athlete recently to have an adverse analytical finding of clenbuterol. In recent years, there have been a number of cases with adverse analytical findings involving clenbuterol and in several of these, it has followed the alleged unknowing consumption of contaminated meat (presumably contaminated following its unlawful use during the farming process). It is also notable that clenbuterol has been found in various food products and has even caused food poisoning in various countries. 

In particular, there have been contamination or food poisoning cases in China and Mexico (denied by both governments), but cases have also been reported in Hong Kong, Portugal, France and Spain. In April 2011, Germany's anti-doping agency, Nationale Anti-Doping Agentur (NADA), advised against athletes eating products containing meat when travelling to Mexico or China because it might increase the risk of involuntary positive doping results. 

Alessandro Colo 
Italian road cyclist Alessandro Colo tested positive for clenbuterol in April 2010 after the last stage of Vuelta Mexico. The Italian Cycling Federation passed the case onto the Italian Anti-doping Agency (CONI). In October 2010, CONI ruled that although Colo had tested positive, there was “no fault or negligence” on his part and the usual 2 year ban was reduced to 1 year. It considered that he had tested positive following the “accidental consumption” of contaminated meat eaten in Mexico and which meant that his ban ran from 21 May 2010 to 20 May 2011. The UCI and WADA did not appeal this ruling. 

Mexican footballers
Five players from the Mexican national team tested positive for clenbuterol in June 2011 following a test during a training camp in May 2011. The five players were goalkeeper Guillermo Ochoa, defenders Francisco Rodriguez and Edgar Duenas, and midfielders Antonio Naelson 'Sinha' and Christian Bermudez. The Mexican Football Federation (Femexfut) claimed that they had eaten contaminated meat (beef or chicken) between 17 and 20 May 2011, while they were staying at the High Performance Centre in Mexico. Whilst Femexfut seemed to acknowledge there was a problem in Mexico with food contaminated with clenbuterol and investigated meat supplies to the centre, the Mexican Department of Health has strenuously denied there was a problem. The players were banned from playing in the Concacaf Gold Cup in June 2011 in the United States and faced bans of up to 2 years. It appears that following testing of the B samples, in early July 2011 Femexfut cleared all the players and said they would not face a ban after its disciplinary commission findings showed the positive tests were “due to contaminated food”. FIFA has publicly supported Femexfut’s decision, but it is too early to say whether WADA will intervene and appeal this decision to CAS.

Philip Nielsen
Danish road cyclist Philip Nielsen tested positive for clenbuterol in April 2010 after the last stage of Vuelta Mexico. His B sample was also positive in January 2011 and the Danish Cycling Union passed the case onto the Danish Sports Federation (DIF) in March 2011, but the DIF considered there was “no fault or negligence” on Nielsen’s part and cleared him of the doping charges even though he had tested positive. The UCI received the complete decision on 22 March 2011 and requested the complete file on 1 April 2011. To date, it does not appear as if the UCI or WADA are intending to appeal this decision to the CAS. 

Dimitrij Ovtcharov
Beijing Olympics silver medallist Dimitrij Ovtcharov tested positive for clenbuterol in August 2010 but claimed he had eaten contaminated meat from China. He was able to provide evidence of the supply of the meat and relied upon the same “no fault or negligence” defence which is probably being used by Contador. In January 2011, the German Table Tennis Federation (DTTB) ruled that he had probably not deliberately ingested clenbuterol and therefore had no case to answer. WADA elected not to appeal the DTTB’s decision to CAS as it considered there were insufficient ground to warrant an appeal. 

Adam Serocznski
Polish canoeist Adam Serocznski tested for clenbuterol in August 2008 at Beijing Olympics and was banned for 2 years from September 2008. In August 2009, the CAS rejected a claim by him that his positive test was the result of “food contamination” following the ingestion of contaminated meat fed by the organisers. The expert witness of the International Olympic Committee (IOC) rejected the assertion of a possibility of food contamination and his ban was upheld. 

Rudi van Houts
Dutch mountain biker Rudi van Houts tested positive for clenbuterol in late October 2010 in out-of-competition testing in Mexico. His B sample was probably tested in December 2010 and the Dutch Cycling Federation (KNWU) handled the Adverse Analytical Finding. In March 2011, van Houts was cleared of doping charges by the KNWU. To date, it does not appear as if the UCI or WADA are intending to appeal this decision to the CAS. 

WADA laboratory accreditation and detectability of clenbuterol 

The WADA protocols for accreditation of testing laboratories stipulate that the methodology used must be capable of detecting clenbuterol in urine at a concentration of 2 ng/ml. This is referred to as the Minimum Required Performance Level (MRPL) and is the “analytical parameter of technical performance with which the [WADA-accredited] laboratories shall comply when testing for the presence of a particular Prohibited Substance, its Metabolite(s) or Marker(s)” [WADA Technical Document - TD2010MRPL, effective from 1 September 2010]. 

With the possibility that some laboratories can identify a wider or lower range of concentrations of clenbuterol than other laboratories, there is the potential for inconsistent adverse analytical findings. For example, one accredited laboratory could be capable of detecting clenbuterol down to concentrations of 0.1 ng/ml and another accredited laboratory could have equipment that could only detect down to 1 ng/ml. Both laboratories would be accredited but if for example an athlete’s sample contained 0.5 ng/ml of clenbuterol, whether or not that athlete had a detectable adverse analytical finding would depend on which of the two laboratories tested the sample. In addition, there have also been issues raised with regard to the thresholds concentrations at which clenbuterol can be detected using current technology, where the low signal-to-noise ratio makes quantification problematic. 

It appears the issue of quantification prompted an investigation into the limits of detection specified by WADA’s accreditation processes and an investigation of how this compared to the technology available for detection. It is likely that further investigations are necessary with regard to the levels of clenbuterol associated with pharmacological activity, the window post-dosing during which it remains detectable in urine, its (unlawful) use as a bulking agent for animals and the effects of its entry into the food chain via tainted meat. 

There was recent speculation that WADA might change its rules regarding clenbuterol by implementing a fixed level of clenbuterol over which there would be no defence to an adverse analytical finding. These speculations probably arose as a result of a scheduled meeting of WADA experts and the mounting media interest prompted WADA to issue a press statement which clarified its position. The WADA statement released on 15 June 2011 said: “It is possible that under certain circumstances the presence of a low level of clenbuterol in an athlete sample could be the result of food contamination. However, each case is different and all elements need to be taken into account. …No decision will be taken at this meeting [in June 2011] and any recommendation [regarding clenbuterol] will then be reviewed and discussed at the WADA Health, Medical and Research Committee in view of the preparation of the 2012 List [of Prohibited Substances].” 

In summary, the WADA statement said that it did not currently plan to introduce a threshold level but recognized the potential for tainted food to give rise to an adverse analytical finding. In any event, any proposed changes would have required WADA board approval and it is possible that any major changes may not be forthcoming until the global conference scheduled for 2013, when the World Anti-Doping Code will be revised. 


The pursuit of drug-free sport has never been easy or simple and has been a constant battle between the dopers and those involved in testing and catching the dopers. Evidence of food contamination, variability of detectability between laboratories and technological advances only add to the complexity of cases where clenbuterol is involved. There are many people who will be watching closely the outcome of the appeal before the CAS in the Contador case, but that is unlikely to be end of the story where clenbuterol is involved. 

Dr Sam Samaratunga 
Solicitor at Arnold & Porter (UK) LLP, London 20 July 2011