Clenbuterol is a long-acting asthma drug that stimulates beta-2 receptors. Bodybuilders use it for fat loss and to hold muscle while dieting. It raises heart rate, body temperature and metabolism, and it has caused serious heart problems and poisonings.
- In some countries it is prescribed for asthma at 20–40 micrograms twice a day.
- In Canada it is approved only for horses.
- Fast heart rate, tremor, low potassium and heart rhythm problems are the main dangers.
Clenbuterol is one of the most talked-about cutting drugs. It works, modestly, and it is also among the most common causes of performance-drug poisoning calls to poison centres. Here is the full picture.
What clenbuterol is
Clenbuterol is a beta-2 adrenergic agonist, the same family as salbutamol (Ventolin), but much longer acting, with a half-life of about 25–39 hours. It opens the airways and, at higher amounts, stimulates metabolism. In some European and other countries it is prescribed for asthma. In Canada and the United States it is not approved for people; in Canada it is approved only as a veterinary drug for horses with airway disease.
Why it is used for cutting
- Raises metabolic rate and body temperature, burning extra calories
- Increases fat breakdown (lipolysis)
- Anti-catabolic effects: in livestock and animal studies it increased muscle and reduced fat, which is why it was illegally used in cattle and pigs
In humans, the fat-loss effect is modest and fades over a few weeks as beta-2 receptors become less responsive (downregulation). Most of the muscle effects come from animal research.
Side effects
- Fast heart rate and palpitations
- Tremor, especially in the hands
- Anxiety, restlessness and insomnia
- Sweating and raised body temperature
- Headache
- Muscle cramps from low potassium and taurine depletion
- Raised blood pressure
The serious risks
Medical journals report heart attacks, abnormal heart rhythms (including atrial fibrillation and supraventricular tachycardia), heart muscle damage and dangerously low potassium in young, otherwise healthy people using clenbuterol. Poison centre studies in the United States have described a rise in clenbuterol cases linked to weight-loss and bodybuilding use. Food contaminated with clenbuterol from illegally treated livestock has also caused outbreaks of poisoning abroad.
Who should never use it
- Anyone with heart disease, an irregular heartbeat or high blood pressure
- Anyone with an overactive thyroid
- Anyone with an anxiety or panic disorder
- Anyone using other stimulants, thyroid hormone or diuretics
- Pregnant or breastfeeding women
Combinations that raise the risk
Clenbuterol is often combined with T3 thyroid hormone, yohimbine, caffeine or diuretics in contest preparation. Each adds to heart strain, and diuretics make low potassium worse. See our guides to T3, yohimbine and diuretics.
Monitoring if used
- Resting heart rate every morning; a rise of more than about 20 beats per minute above normal is a warning sign
- Home blood pressure
- An ECG before use if you are over 35 or have risk factors
- Blood potassium and magnesium, kidney function and fasting glucose
Arrange tests through your doctor or privately at LifeLabs or Dynacare. See our bloodwork guide.
Clenbuterol in food and sport
Because clenbuterol makes livestock leaner, it has been used illegally in cattle and pigs in some countries. People who ate contaminated meat have been poisoned, with tremor, palpitations and headache, and athletes have tested positive after eating meat abroad. Canada does not permit clenbuterol in food animals, and the Canadian Food Inspection Agency tests for drug residues. For athletes, the World Anti-Doping Agency has warned about contaminated meat in certain countries, but a positive test is still treated seriously. Clenbuterol is banned at all times in sport.
Is it worth it?
For most people, the extra fat loss from clenbuterol is small compared with what a consistent calorie deficit, enough protein and daily steps achieve, and the heart risks are real. See cutting without losing muscle and safer cutting options.
Products and legal status
We carry Zionova Clenbuterol 50 mcg and Genetix Clen 75 for research, with batch lab results on each page. Clenbuterol is not approved for human use in Canada and is banned in sport at all times.
Frequently asked questions
Is clenbuterol a steroid?
No. It is a beta-2 agonist, related to asthma inhalers such as salbutamol but much longer acting.
Is clenbuterol legal in Canada?
It is approved in Canada only as a veterinary drug for horses. It is not approved for human use and is banned in sport.
Why does clenbuterol stop working?
Beta-2 receptors become less responsive with continuous use, so its effects fade over a few weeks.
Photo: medipics1066, Wikimedia Commons (CC BY 2.0).
General information, not medical advice. Clenbuterol is not approved for human use in Canada.
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