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What Is Clenbuterol

Medically reviewed by Jenny Yu, MD FACS — By Jill Seladi-Schulman, Ph.D. — Updated on October 20, 2022Clenbuterol is a compound that belongs to a class of drugs called beta2-agonists. Drugs in this category can cause dilation of the bronchial muscles. Beta2-agonists are often used to treat asthma. In addition to being used to treat asthma, clenbuterol has become popular as a weight loss supplement. That’s because of its effect on muscle growth and fat reduction. Read on to learn more about the usage, safety, and side effects of this medication.

Clenbuterol usage

The Food and Drug Administration (FDA) hasn’t approved clenbuterol for use in humans. A liquid form of the drug is approved by the FDA for treatment of airway obstruction in horses. Outside the United States, clenbuterol is available by prescription only for the treatment of asthma. It’s also sometimes prescribed for the treatment of chronic obstructive pulmonary disease (COPD). Clenbuterol isn’t a steroid, but it has properties similar to anabolic steroids, such as promoting an increase in muscle mass. Due to these properties, clenbuterol has been used in livestock to increase the amount of lean muscle. The drug can still be found in the meat of livestock after it has been butchered, and this has led to illness in Europe and Asia. Because of this, the United States and Europe monitor tissue samples from livestock in order to detect the presence of clenbuterol. Clenbuterol has also been observed as an additive in illegal drugs, such as heroin.

Weight loss and performance enhancement

Clenbuterol has been observed to both increase muscle mass and reduce body fat. Additionally, it remains in the body with an active effect for about 6 days after consumption (detectable traces can remain longer). Because of these properties, it’s often used as a weight loss supplement or to enhance athletic performance. People taking clenbuterol for weight loss or performance enhancement often use anabolic steroids or growth hormones as well. Studies on the efficacy of clenbuterol as a weight loss or performance enhancer in humans are quite limited, although many studies have been performed in animals and livestock:Researchers have observed that clenbuterol stimulates muscle growth and repair while preventing atrophy in mice and rats.Studies in livestock have indicated that the increase in muscle growth occurs at the expense of fat tissue. This is part of a process referred to as repartitioning.A study in horses found that long-term administration of high doses of clenbuterol increased the expression of genes related to various muscle components and fat metabolism. Even though there is minimal evidence for clenbuterol as a performance-enhancing drug, it’s listed on the World Anti-Doping Agency’s Prohibited List.

Clenbuterol side effects

Clenbuterol can have side effects when overused or misused. These can include:increased heart raterapid breathingheart palpitationschest paintremorsanxietyelectrolyte imbalance A review of adverse reactions to clenbuterol reported to two poison control centers found that 11 of the 13 cases were due to clenbuterol use for weight loss or bodybuilding.

Dosage and administration

When clenbuterol is taken to control asthma symptoms, the recommended dosage is between 0.02 and 0.03 milligrams per day. The medication comes in tablet or inhaler form for asthma treatment. Like many bronchodilators used for asthma treatment, you should use it as needed — up to the recommended dosage as opposed to regular daily use. Clenbuterol used for weight loss or performance enhancement can be acquired as a tablet, liquid, or injection. People using clenbuterol for this purpose typically use between 0.06 and 0.12 milligrams per day, which is higher than the recommended dosage for asthma treatment.

The takeaway

Clenbuterol isn’t approved by the FDA for use in humans. Outside the United States, it can be used to treat asthma or COPD. The drug is often used off-label for weight loss or to enhance athletic performance. Clenbuterol is on the World Anti-Doping Agency’s Prohibited List. Professional athletes testing positive for this drug can be disqualified from participating in competitive sports. Clenbuterol can have negative side effects when overused or misused. It’s important to strictly follow all dosage guidelines when using clenbuterol. Last medically reviewed on October 20, 2022

How we vetted this article

SourcesHistoryHealthline has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.Clenbuterol. (2019).
deadiversion.usdoj.gov/drug_chem_info/clenbuterol.pdfKnych HK, et al. (2016). Differential expression of skeletal muscle genes following administration of clenbuterol to exercised horses.
ncbi.nlm.nih.gov/pmc/articles/PMC4979108/Spiller HA, et al. (2013). A descriptive study of adverse events from clenbuterol misuse and abuse for weight loss and bodybuilding.
pubmed.ncbi.nlm.nih.gov/23844963/Spurlock DM, et al. (2006). Changes in skeletal muscle gene expression following clenbuterol administration.
ncbi.nlm.nih.gov/pmc/articles/PMC1766935/Wannenes F, et al. (2012). In vitro effects of beta-2 agonists on skeletal muscle differentiation, hypertrophy, and atrophy.
ncbi.nlm.nih.gov/pmc/articles/PMC3651181/The world anti-doping code international standard: Prohibited list. (2018).
wada-ama.org/sites/default/files/prohibited_list_2018_en.pdfYen M, et al. (2012). Toxicity of weight loss agents.
link.springer.com/article/10.1007/s13181-012-0213-7Our experts continually monitor the health and wellness space, and we update our articles when new information becomes available. Current Version Oct 21, 2022 By Jill Seladi-Schulman, PhD Edited By Aline (Ren) Dias Medically Reviewed By Jenny Yu Copy Edited By Copy Editors Mar 29, 2019 By Jill Seladi-Schulman, PhD VIEW ALL HISTORY Share this articleMedically reviewed by Jenny Yu, MD FACS — By Jill Seladi-Schulman, Ph.D. — Updated on October 20, 2022

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