Is Clenbuterol Safe?

Written by tracii hanes
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Clenbuterol is a bronchodilator and smooth muscle relaxant sometimes prescribed to treat asthma outside the U.S. Due to its thermogenic (metabolism boosting) and stimulant effects, clenbuterol is sometimes abused as a weight loss aid or performance-enhancing drug.

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Clenbuterol--closely related to the asthma medication albuterol--is not approved for human use in the U.S. but is sometimes prescribed for asthma in other countries. It is also used in veterinary medicine for respiratory problems in horses and as a growth-stimulating agent in pigs and other livestock.


Clenbuterol raises body temperature, stimulates the release of adrenalin and speeds metabolism. It also relaxes smooth muscle, making it an effective bronchodilator. Other effects include increased alertness, insomnia and sweating.

Adverse Reactions

Like other stimulants, clenbuterol can raise blood pressure, cause tachycardia (rapid heart rate) and increase the risk for adverse cardiovascular events such as heart attack and stroke. According to the U.S. Department of Justice, clenbuterol has been linked to heart failure in horses, though it's not clear whether this applies to human use as well.

Legal Status

While not a controlled substance in the U.S., clenbuterol has been banned by the World Anti-Doping Agency for use by Olympic athletes, according to the U.S. Department of Justice.


Because clenbuterol is not regulated by the FDA for human use, it may be more likely to contain harmful impurities. If you experience rapid heart beat, chest pain, difficulty breathing or other severe symptoms while taking clenbuterol, seek immediate medical attention.

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