What Is Clenbuterol?

Medically reviewed by Alan Carter, PharmD on January 18, 2018Written by Jill Seladi-Schulman PhD on January 18, 2018

Overview

Clenbuterol 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 for this medication.

Clenbuterol usage

The 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 of 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 some properties similar to those of 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 recently been observed as an additive in street 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 up to about 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:

  • have observed that clenbuterol stimulates muscle growth and repair while preventing atrophy in mice and rats.
  • 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 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.

Despite the fact that there is minimal evidence for clenbuterol as a performance-enhancing drug, it’s listed on the .

Clenbuterol side effects

Clenbuterol can have negative side effects when overused or misused. These can include:

A review of adverse reactions to clenbuterol reported to two poison control centers found that 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 of 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 (WADA) 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.

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