Clenbuterol: Uses, Side Effects, Risks

Banned Respiratory Treatment

Clenbuterol is a beta agonist. In some parts of the world, it is used to treat breathing difficulties caused by conditions such as asthma or chronic obstructive pulmonary disease (COPD). In the United States, however, clenbuterol is not approved for this purpose. What's more, it has been used illegally by athletes as a performance enhancer similar to anabolic steroids.

Clenbuterol can be inhaled, injected, or taken by pill
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What It Does

Beta agonists copy the effect of hormones called catecholamines—specifically epinephrine but also norepinephrine and dopamine. They act on the smooth muscle of the bronchi and bronchioles (the airways in the lungs), uterus, and the intestines as well as some blood vessels in the body by targeting beta adrenergic receptors in these locations.

Beta agonists prevent smooth muscles from contracting. They sometimes are used as tocolytics, medications that can delay labor by relaxing the smooth muscle of the uterus.


Beta agonists including clenbuterol are strong bronchodilators, drugs that can increase the diameter of the airways. They accomplish this by relaxing the smooth muscle tissue of the breathing tubes.

Since they open the airways, beta agonists can effectively treat asthma, COPD, and other conditions in which breathing is difficult because inflammation and/or mucus blocks the bronchioles and prevents airflow.

Bronchodilation is far from the only effect that beta agonists have on the body, however, and multiple beta agonists exist each one having a slightly different profile including toxicity level, duration of effects, and potential for harmful side effects.

Clenbuterol is similar in profile to another beta agonist called albuterol. Clenbuterol is a long-acting beta agonist. Clenbuterol is not typically used because there are similar drugs available that have the same desired effects on the breathing passageways but are less likely to cause dangerous side effects.

Clenbuterol Side Effects

Common side effects of beta agonists including clenbuterol may include:

  • Increased heart rates
  • Musculoskeletal tremors
  • Headache
  • Nausea

Clenbuterol has stimulant effects, which can lead to other potential side effects such as:

Over time, some users build up a tolerance to these types of medications.

Anabolic Effects

Most of the studies showing anabolic effects of clenbuterol have been done on animals, but, at least one small study done on humans with chronic heart failure did show an increase in lean mass and decrease in body fat. However, this same study also showed that endurance (the length of time these individuals were able to exercise) actually decreased.

Studies on rats have shown similar effects on lean muscle mass and decreased body fat. It is also interesting to note that a study on rats showed that albuterol has similar anabolic effects at safer doses.

Clenbuterol Side Effects Long Term

These studies are the basis of the abuse of clenbuterol in athletes. However, significant large-scale studies on humans on clenbuterol have not been conducted, and long-term effects on humans using clenbuterol for this purpose have not been done.

While case reports of dangerous side effects and even death are not lacking, much remains unknown about the effects of clenbuterol on people.

How Is Clenbuterol Used

When used for breathing difficulties, beta agonists are usually inhaled. Using a metered-dose inhaler may help to mitigate the side effects of the medication. However, other forms of this medication exist, including oral pills, syrups, and injectable forms.

Clenbuterol is a long-acting beta agonist, so in countries where it is used for the treatment of asthma, it should be used in conjunction with a short-acting beta agonist or rescue medication (inhaled corticosteroid) rather than used alone.

When used for its anabolic properties this medication is often taken in very large doses either orally or injected, which increases the likelihood of experiencing dangerous side effects.

Clenbuterol is banned by most sports organizations, including the World Anti-Doping Agency (WADA), International Olympic Committee (IOC) and the United States Olympic Committee. Athletes are tested for it before a competition.

Dangers and Abuse

Clenbuterol is not approved in many countries due to its potential to become toxic at even very low doses. Harmful side effects may include tachycardia, heart palpitations, tremors, seizures, increased blood sugar, cardiac arrest, and even death. These dangerous side effects are more likely to occur when the drug is used at high doses.

In the United States clenbuterol is sold on the black market, sometimes under the street name "clen." it is often purchased by bodybuilders or athletes for its alleged abilities to decrease body fat and increase muscle mass.

Female athletes seem to be more likely to abuse the drug than male athletes because clenbuterol side effects for female aren't the typical issues associated with anabolic steroids such as facial hair, deepening of the voice, and thickening of the skin.

It has also been mixed with heroin, possibly for its stimulant properties, and there have been cases of hospitalization and even death after individuals have used heroin laced with clenbuterol.

Treatment for Clenbuterol Abuse

Clenbuterol poisoning can be treated. If you or someone you know has ingested too much of this medication it is important to get emergency medical attention right away. You can call Poison Control or 911, or head to the emergency room.

Potential treatments may include intravenous fluids or medications called beta blockers to lower the heart rate. Sedatives are sometimes given to mitigate the stimulant properties of clenbuterol.

Veterinary Use

There is only one medication containing clenbuterol that is approved for use in the United States. Ventipulmin is a syrup containing a small amount of clenbuterol that is approved by the Food and Drug Administration for use in horses to treat respiratory obstruction.

In the past, clenbuterol has been used in livestock as a means to increase lean muscle mass. Currently, clenbuterol is prohibited in the United States for use in any livestock used for food because the drug will be present in the meat after the animal is slaughtered. Consuming this meat may be dangerous.

Some athletes have claimed to have ingested contaminated meat when they have tested positive for clenbuterol prior to athletic events. In some countries, clenbuterol is used in pregnant cattle to prevent early labor.

Frequently Asked Questions

  • Is clenbuterol banned?

    Yes. In the United States, the sale and purchase of clenbuterol is prohibited. It can not be prescribed for use in humans nor animals.

  • Does clenbuterol have long-term side effects?

    It's not clear what the long-term effects might be since there is limited research that tracks clenbuterol use. Some studies done on mice show that it could help with muscle growth when taken long-term, but it might also be a negative effect on endurance and problems with deformities,

  • Does clenbuterol help you lose weight?

    Clenbuterol can cause rapid weight loss because it increases your metabolic rate. It also helps with fat loss. However, the side effects and dangers of clenbuterol make it inappropriate to use as a weight loss aide.

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Verywell Health 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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By Kristin Hayes, RN
Kristin Hayes, RN, is a registered nurse specializing in ear, nose, and throat disorders for both adults and children.