Clenbuterol
Clenbuterol hydrochloride
A veterinary/asthma drug abused for fat loss — heart-toxic.
Banned / Harmful evidence
☠️Banned & Harmful
Evidence tier
Banned / Harmful
Research weight
Not supported
Citations
12 verified / 12
Classification
Banned & Harmful
⊘
What the evidence says. Linked to serious harm and/or banned in sport and many jurisdictions. Listed for awareness and safety only — NOT a recommendation.
⚠
Health warning. Clenbuterol is not an approved human medicine in many countries and is not a dietary supplement. Abused for fat loss and muscle 'hardening', it strains the heart and has caused poisoning outbreaks. Banned in sport.
What is Clenbuterol?
Clenbuterol (Clenbuterol hydrochloride) is a banned or harmful substance marketed for fat loss. NutriDex grades the human evidence as Banned / Harmful. Clenbuterol is a β2-agonist used in some countries for veterinary purposes and, abroad, for asthma. It is abused in bodybuilding and 'celebrity' weight-loss circles for its fat-burning and anti-catabolic effects. It is not a dietary supplement and is not approved for human use in the US. It overstimulates the heart and has caused mass poisonings from contaminated meat. It is banned by anti-doping agencies.
Marketed Claims (unproven)
✕(Claimed) fat loss
✕(Claimed) muscle preservation / 'hardening'
Dosing & Compounds
Use & Legality
Not an approved human supplement or medicine (in the US); no safe self-administered dose.
Active Compounds
Safety & Cautions
⚠ Rapid/irregular heartbeat, tremor, anxiety, low potassium, chest pain and cardiac muscle damage. Overdose risk is high because illicit products are unregulated. Not approved for human use in the US; banned in sport. Educational only — always check with your doctor or pharmacist before combining Clenbuterol with any medicine.
Evidence & Risk Findings ★ 12 studies
systematic review
Saif et al. 2023 (Int J Legal Med)
✓ PubMed
Systematic review of 23 studies (24 athletes) found clenbuterol misuse, mostly oral at 20 ug to 30 mg/day, caused predominantly cardiac adverse events including supraventricular tachycardia, atrial fibrillation, myocardial injury, myocarditis, infarction, cardiomyopathy and death.
rct
Hostrup et al. 2025 (J Physiol)
✓ PubMed
Randomized placebo-controlled trial in healthy young men found a 2-week oral clenbuterol cycle increased lean mass and raised skeletal muscle protein content by about 17%, but impaired VO2max/cardiorespiratory fitness and desensitized muscle beta2-adrenergic signalling after 2 weeks.
clinical-trial
Jessen et al. 2020 (Drug Test Anal)
✓ PubMed
Human study in six young men showed clenbuterol increased resting energy expenditure by 21% and fat oxidation by 39%, and raised skeletal muscle mTOR-Ser2448 phosphorylation by 121% and PKA substrate phosphorylation by 35%.
Agency / regulator
WADA Prohibited List
✓ Source
Clenbuterol is banned in sport at all times.
agency
Poison Control (National Capital Poison Center)
✓ Source
Authoritative statement notes clenbuterol is not FDA-approved for human use and is unsafe, with claimed muscle/fat benefits shown only in livestock and animal studies, while human misuse causes cardiac, muscular and metabolic toxicity.
review
Kataveni et al. 2025 (Cureus)
✓ PubMed
Narrative review of unsupervised clenbuterol use in bodybuilding/athletics reports cardiovascular harms (arrhythmias, hypertension), muscle spasms and broader physiological toxicity, plus inadvertent exposure via contaminated meat.
Review
Low Dose Clenbuterol Toxicity 2023
✓ Full text
Case report and literature review documenting that clenbuterol toxicity is increasingly seen in US hospitals among young athletes/bodybuilders, with effects (nausea to myocardial ischemia, rhabdomyolysis, cardiogenic shock) not correlating with ingested dose and managed only with supportive care as no antidote exists.
Safety / toxicology
Poisoning outbreaks
✓ PubMed
Tachycardia, tremor and cardiac symptoms reported after contaminated-meat exposures.
observational
Spiller et al. 2013 (Subst Abus)
✓ PubMed
Poison-center descriptive study of 13 clenbuterol users misusing it for weight loss/bodybuilding documented tachycardia, widened pulse pressure, hypokalemia, hyperglycemia, ST changes and elevated troponin, with myocardial injury in 2 patients and effects persisting beyond 24 hours.
Cohort
Brett 2014 (NSW Poisons Information Centre, retrospective cohort)
✓ PubMed
Retrospective poison-center series of 63 clenbuterol exposures (2004-2012), rising sharply from 3 in 2008 to 27 in 2012; 84% (53 patients) required hospitalization. Commonest reasons were bodybuilding and slimming; commonest features tachycardia (24), GI disturbance (16), tremor (11), with cardiotoxicity including one cardiac arrest in a 21-year-old man. DOI: https://doi.org/10.5694/mja13.10982
case-series
Hieger et al. 2016 (J Emerg Med)
✓ PubMed
Case series of 10 hospitalized patients with clenbuterol-adulterated heroin exposure presented with chest pain, palpitations and dyspnea plus severe hypokalemia (K nadir 2.5 mEq/L), hyperglycemia and lactic acidosis; all survived with supportive care.
Study
Cardiac literature
✓ PubMed
β2-agonist overstimulation can cause arrhythmia and cardiac muscle damage.