Clenbuterol is approved for use in humans to help treat asthma in some countries but is banned for this purpose in the United States. Side effects of the drug include anxiety, shaking, headaches, heart dysfunction, and more.

Clenbuterol is a chemical called a beta-2-adrenergic agonist. It has approval in the United States for use in horses with breathing difficulty.

Clenbuterol is both a decongestant and a bronchodilator. A decongestant works by narrowing and constricting blood vessels to reduce congestion. Conversely, a bronchodilator helps relax the muscles around the airway, which in turn opens it up.

In some European and Latin American countries, clenbuterol has approval for human use as an asthma drug. Others have used it to treat chronic obstructive pulmonary disease (COPD). However, in the United States, its use is banned for these purposes.

The drug is also controversial due to its use in bodybuilding and weight-loss programs.

This article looks at how clenbuterol works, its uses, and risks.

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As a beta-2-adrenergic agonist, clenbuterol stimulates the heart and central nervous system, so it has the opposite effect as a beta-blocker. It has a similar stimulating effect on the body as epinephrine and amphetamines.

This stimulation leads to various effects, such as:

  • rapid fat burning
  • excitability
  • nervousness
  • increased energy
  • greater determination

Clenbuterol’s initial use was as an asthma drug. However, bodybuilders, performance athletes, and those wanting to lose weight are now using it.

Some people use clenbuterol as a weight-loss aid, as it can increase a person’s metabolism. As well as reducing body fat and weight, it allows the user to retain both muscle mass and body strength at the same time.

Clenbuterol became known as a “celebrity diet secret” because of its apparent use by celebrities and famous athletes.

One study reviewed data from two regional poison centers in the United States. It found that in 11 of the 13 reported cases of those taking clenbuterol, people had used it for weight-loss reasons or as part of a bodybuilding program.

The World Anti-Doping Agency has banned the use of clenbuterol at all times, both in and outside of competition.

Athletes and bodybuilders taking clenbuterol will often work on a program cycle that includes on and off periods.

The dosage can vary depending on factors that include gender and tolerance. People can take it orally or via injection, but both methods carry risks. Injections can cause scarring or air bubbles to form in the blood, while oral tablets can affect the liver.

When people use it in Europe and Latin America to open the airways in those with asthma, the recommended dose is 0.02–0.03 milligrams daily.

Clenbuterol is banned in many countries and has become controversial due to its association with many side effects.

Many of these side effects are the same as those relating to amphetamines, including:

An older 2007 study found that clenbuterol can also negatively affect the heart, causing some symptoms such as:

Beta-agonists such as clenbuterol have the potential to negatively affect the heart by causing or exacerbating symptoms such as heart palpitations and atrial fibrillation.

Increased heart rate and dilation from using the drug can lead to cardiac hypertrophy. This condition is when the heart grows to an atypical size, which in turn can lead to a heart attack and eventually death.

Many countries have banned clenbuterol from being used in animals that humans will consume.

In 1994, 140 people in Spain required hospitalization after eating meat containing clenbuterol. Similarly, in 2006, 336 people in China were poisoned after eating pork containing the drug.

Clenbuterol can reduce the amount of naturally occurring potassium in the body. Consequently, those taking it as a drug will often also eat extra portions of bananas to replace the substance.

Athletes will often combine taking clenbuterol alongside a diet high in protein, moderate in carbohydrates, and low in fat.

There has been an increase in clenbuterol use as a drug for bodybuilding and weight-loss purposes, with people obtaining it online.

However, due to the hidden dangers of the drug, there can be serious risks for those who take it regularly.

The Department of Emergency Medicine in Newton, MA, reported two cases of people requiring medical attention and treatment due to clenbuterol use.

The individuals were bodybuilders ages 18–22 years who experienced heart palpitations, nausea, vomiting, and chest pain shortly after taking clenbuterol.

The Peking Union Medical College in Beijing, China, found that low doses of clenbuterol had minimal effects when the researchers tested them on rabbits. However, medial doses significantly affected the animals’ heart rates, and higher doses even led to death.

Some interesting research suggests clenbuterol use could have merit in diabetes management. In a 2023 randomized control trial, healthy male subjects experienced enhanced insulin sensitivity and improved skeletal muscle glucose uptake from clenbuterol.

A 2022 animal study found similarly encouraging results.

Clenbuterol’s effects on the heart and muscles depend on how high a dose someone has been taking and for how long. The risks increase with the dose and duration.

Those taking high doses can quickly experience long-term side effects, such as a change in the heart’s size, weight, strength, and activity.

Clenbuterol is illegal for human consumption in the United States due to its hazardous health effects, and anyone buying the drug online should exercise extreme caution.

While some people may take the risk due to the less harmful side effects, they should always consider clenbuterol’s potentially extreme side effects.