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June 12, 2019


Clenbuterol belongs to the so-called beta-2-agonists. Its chemical structure resembles that of adrenaline. It stimulates the beta-2-receptors of the sympathetic nervous system, whereupon the smooth muscles, for instance, in the bronchial tubes and the uterus, relax. Compared with the half-life of other beta-2-receptors, that of clenbuterol is long; it is stronger and its absorption from the alimentary canal is better [1].


Beta-2-agonists are used as asthma medications and to prevent premature childbirth.

Clenbuterol is an orally administered medication. It is used mainly in the field of veterinary medicine: for example, in the treatment of asthma in horses. Clenbuterol is not used to treat asthma in humans. Clenbuterol has also been used illegally for rearing beef cattle, as well as for diluting drugs, such as heroin [1, 2, 3].

There have been attempts to develop clenbuterol into a medicine for diseases, such as sarcopenia, HIV and cancer, which involve decreased muscle mass. However, the potential harm of cardiac origin caused by clenbuterol has prevented such therapies [4, 5].

Several beta-2-antagonists—and clenbuterol in particular—have a minor anabolic (i.e. tissue growth-stimulating) effect. They increase the protein content of striated muscles as the muscle glycogen and body fat burn. That is why clenbuterol is one of the most common substances used for growing muscle mass [1, 6]. Thus far, however, it is not classified as a doping substance under the Finnish Criminal Code (Act 705/2002, Chapter 44, Section 16, Paragraph 1).

Adverse effects

Some of the adverse effects of clenbuterol include tremors, nervousness, headaches, vertigo, palpitations, arrhythmias, muscle cramps, electrolyte disturbances, and even hallucinations and convulsions. Arrhythmias and hypokalemia (i.e. low blood potassium level) can lead to death if they are not treated. Clenbuterol is used quite often together with anabolic steroids, involving a high risk of cardiotoxicity [1, 6, 7, 8]

Some known trade names (9/2014): Spiropent, Ventipulmin.

Timo Seppälä

Medical Director
Finnish Center for Integrity in Sports FINCIS (previously the Finnish Antidoping Agency FINADA)

Updated by

[1] Spiller HA, James KJ, Scholzen S, Borys DJ. A Descriptive Study of Adverse Events from Clenbuterol Misuse and Abuse for Weight Loss and Bodybuilding. Substance Abuse. 2013; 34(3): 306-213
[2] Brambilla G, Cenci T, Franconi F, Galarini R, Macrí A, Rondoni F, Strozzi M, Loizzo A. Clinical and pharmacological profile in a clenbuterol epidemic poisoning of contaminated beef meat in Italy. Toxicol Lett. 2000;114(1–3):47–53
[3] Hieger M, Emswiler M, Maskell K, Sentz J, Miller K, Wolf C, Cumpston K, Wills B. A case series of clenbuterol toxicity caused by adulterated heroin. J Emerg Med. 2016;51(3):259–61
[4] Ryall JG, Lynch GS. The Potential and the Pitfalls of β-adrenoceptor Agonists of the Management of Skeletal Muscle Wasting. Pharmacology & Therapeutics. 2008; 120: 219-23
[5] Lynch G, Ryall J. Role of β-adrenoceptor signaling in skeletal muscle: Implication for muscle wasting and disease. Physiol Rev. 2008;88(2):729–67
[6] Daubert, Mabasa, Leung & Aaron. Acute clenbuterol overdose resulting in supraventricular tachycardia and atrial fibrillation. Journal of Medical Toxicology 2007;3(2): 56–60
[7] Bilkoo, Thomas, Riddle & Kagaoan. Clenbuterol toxicity: an emerging epidemic. A case report and review. Connecticut Medicine. 2007;71(2): 89–91
[8] Capretti, Dantes, De Gasperi & D’Ambrosio. Changes in blood potassium induced by the abuse of 3 beta 2-agonist drugs. Clinica Terapeutica. 1987;121(1): 41–4