What Is Clenbuterol?

A Risky, Banned Performance-Enhancing Drug

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Clenbuterol, also called "clen," is considered a performance-enhancing drug. It's banned from most athletic competitions. The World Anti-Doping Agency and the International Olympic Committee include clenbuterol on their lists of prohibited drugs.

Despite these bans, athletes and others continue using clenbuterol for its ability to help burn fat, build muscle, and improve performance. This is unfortunate because clenbuterol has been linked to several serious side effects.

What Is Clenbuterol?

Clenbuterol is a type of medication that's a selective beta-2 agonist/antagonist and bronchodilator. That means it relaxes the smooth muscle tissue that makes up the airways, allowing for freer breathing.

The United States Food and Drug Administration has approved clenbuterol only for veterinarians, who may prescribe it to treat horses with obstructive pulmonary disease or other lung conditions. The trade name for clenbuterol used for horses is Ventipulmin.

The "human equivalent" of clenbuterol is albuterol, which is a prescription-only medication used to treat or prevent bronchospasm caused asthma, bronchitis, emphysema, and other lung diseases, and also to prevent wheezing caused by exercise.

There are a variety of brand names for albuterol, including Ventolin, Proventil, and Accuneb, among others. Regardless of whether it comes in generic or brand name form, albuterol comes in an inhaler that a person can use to breathe the medication in through the mouth so it can easily reach the airways.

What Does Clenbuterol Do?

Clenbuterol was previously given to livestock to increase lean muscle mass and livestock production. Now it's banned from being used for this purpose. In general, any positive effects of taking clenbuterol seem to be temporary and short-lived. Long-term use could cause health issues, including heart damage.

Athletes who test positive for clenbuterol often claim they must have eaten contaminated meat. Three-time Tour de France winner Alberto Contador may be the most famous athlete to have used this excuse after testing positive for clenbuterol.

Athletes, bodybuilders, and others who use clenbuterol do so for its ability to burn fat, build muscle, and improve sports performance. The drug is believed to increase skeletal muscle development by enhancing muscle protein synthesis. At the same time, it aids in fat loss by increasing resting energy expenditure and fat oxidation.

People often turn to clenbuterol because it enhances the effects of training programs. The drug induces muscle hypertrophy (growth) and thermogenesis (fat burning), which is a banned substance in sports and competition.

Risks and Side Effects

The effects of clenbuterol on athletes who take the drug over a long period aren't known. What is clear is that besides affecting the muscles of the airways, clenbuterol is taken up by other tissues in the body.

Animal studies have shown that clenbuterol use may lead to apoptosis—the death of normal cells—in the muscles, including the heart muscles. For this reason, veterinarians are cautioned against giving the drug to horses who have cardiac issues.

Why is Clenbuterol is Banned?

Clenbuterol may lead to heart attacks and other heart damage, and irregular heart rhythms. Other side effects of clenbuterol use include muscle tremors, increased perspiration, and blood pressure, insomnia, headache, nausea, and vomiting. Clenbuterol is also known to cause mood changes, such as agitation and depression..

Current Research

Newer research has examined clenbuterol for its potential in treating diabetes. Studies on mice have shown noticeable improvements in glucose homeostasis and prevented the metabolic deficits of beta-cell dysfunction and insulin resistance. More research is needed to determine the possible use of clenbuterol for diabetes treatment in humans.

A Word From Verywell

Committing to training and nutrition programs if you are an athlete or bodybuilder can help you realize exceptional results. However, these results are hard-fought and often take substantial time. Some people look for shortcuts and advantages, such as performance-enhancing drugs, but these cost your physical health.

Athletes who choose to rely on a banned performance-enhancing drug risk elimination or disciplinary action for cheating. They also more than likely may be risking their health in ways that may be irreversible. If you need advice regarding sports nutrition or help with getting off performance-enhancing drugs, speak to your health care provider.

Frequently Asked Questions

  • What does clenbuterol do to your body?

    Clenbuterol increases your risk of heart attacks and other heart damage, and irregular heart rhythms. Additional side effects include muscle tremors, increased perspiration, and blood pressure, insomnia, headache, nausea, and vomiting. The drug can also induce mood changes, agitation, and depression.

  • Is clenbuterol banned?

    Clenbuterol is banned by use of athletes by the World Anti-Doping Agency and the International Olympic Committee for use as a performance enhancing drug. Clenbuterol is not controlled under the Controlled Substances Act (CSA).

  • Can clenbuterol be used safely?

    Clenbuterol has may high risk dangers and likely cannot be taken safely unless prescribed and monitored by a healthcare provider. If you have questions or concerns about clenbuterol use, speak to a healthcare provider.

10 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  7. Santos RP, Pereira A, Guedes H, Lourenço C, Azevedo J, Pinto P. Anabolic drugs and myocardial infarction - A clinical case reportArq Bras Cardiol. 2015;105(3):316-319. doi:10.5935/abc.20150111

  8. Journal of Cardiology Cases. Case report and review of clenbuterol cardiac toxicity.

  9. Meister J, Bone DBJ, Knudsen JR, et al. Clenbuterol exerts antidiabetic activity through metabolic reprogramming of skeletal muscle cells. Nat Commun. 2022;13(1):22. doi:10.1038/s41467-021-27540-w

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By Elizabeth Quinn
Elizabeth Quinn is an exercise physiologist, sports medicine writer, and fitness consultant for corporate wellness and rehabilitation clinics.