Clenbuterol
1-(4-Amino-3,5-dichlorophenyl)-2-tert-butyl aminoethanol HCl
Also known as: Ventipulmin · Aeropulmin · Spiropent · Broncodil · Ventilan · NAB-365 · Broncoterol · Bronq-C · Cesbron · Clembumar · Clenasma · Clenbutol · Contrasmina · Contraspasmin · Monores · Novegam · Oxibron · Oxyflux · Prontovent · Ventolase
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Bronchodilator | Initially, 0.8 micrograms/kg (practically: 0.5 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement increase to 1.6 micrograms/kg (practically: 1 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement increase to 2.4 micrograms/kg (practically: 1.5 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement increase to 3.2 micrograms/kg (practically: 2 mL of the commercially available syrup/100 lb. BW) twice daily for 3 days; if no improvement discontinue therapy. | PO | q12h | Recommended duration of therapy is 30 days; then withdraw therapy and reevaluate. | 🌎 NA |
| Adjunctive treatment for dystocia emergencies | 300 micrograms per 500 kg mare IV slowly | IV | Single dose | — | 🌎 NA |
| Adjunctive treatment for dystocia emergencies | 10 mls of clenbuterol syrup orally as the mare walks in the door. | PO | Single dose | — | 🌎 NA |
- Bronchodilator: ARCI UCGFS Class 3 Drug
- Adjunctive treatment for dystocia emergencies: Parenteral formulation not available commercially in the USA. Fast onset allows quick decision if uterine relaxation will correct the problem. May be used with sedatives/analgesics; xylazine or detomidine may potentiate uterine relaxant effects.
- Adjunctive treatment for dystocia emergencies: Author's hospital protocol upon arrival of a dystocia.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Clenbuterol is a potent, long-acting beta-2-adrenergic agonist primarily utilized in equine medicine as a bronchodilator to manage airway obstruction diseases such as Recurrent Airway Obstruction (RAO), formerly known as Chronic Obstructive Pulmonary Disease (COPD) or "heaves".
Beyond its respiratory applications, it is occasionally used as a uterine relaxant (tocolytic) to assist in the management of dystocia in mares.
Key Clinical Points:
- Strictly Banned in Food Animals: Clenbuterol acts as a repartitioning agent (increasing muscle mass and decreasing fat) at high doses. Its use in food-producing animals is strictly prohibited globally due to severe, well-documented relay toxicity in humans consuming tainted meat (causing severe tremors, tachycardia, and hospitalization).
- Abuse Potential: Due to its anabolic-like effects, it is frequently abused in human bodybuilding and weight-loss circles. Veterinarians must be vigilant against drug diversion.
- Endocrine & Cardiac Effects: Chronic administration in horses can lead to decreased aerobic performance, cardiac hypertrophy, myocardial collagen infiltration, and altered immune function.
Mechanism of action
Clenbuterol selectively binds to and activates beta-2 adrenergic receptors on smooth muscle cells.
Primary Pathway:
Beta-2 Receptor Activation → Stimulates G_s proteins → Activates Adenylyl Cyclase → Increases intracellular cyclic AMP (cAMP) → Activates Protein Kinase A (PKA) → Decreases intracellular calcium concentrations → Results in smooth muscle relaxation (bronchial, vascular, and uterine).
Secondary Mechanisms:
- Anti-inflammatory Effects: Inhibits the release of pro-inflammatory cytokines (such as Interleukin-1β and Tumor Necrosis Factor-α) from pulmonary macrophages.
- Mucociliary Clearance: Increases ciliary beat frequency in the respiratory tract, enhancing the clearance of excessive mucus associated with RAO.
Safety & warnings
Contraindications
- Food-producing animals (strictly banned by law)
- Horses suspected of having cardiovascular impairment
- Pregnant mares near full-term (unless used specifically for dystocia management)
Adverse effects
- Muscle tremors
- Sweating
- Restlessness
- Urticaria
- Tachycardia
- Creatine kinase (CK) elevations
- Ataxia (rare)
- Abortion in pregnant animals
- Cardiac hypertrophy and collagen infiltration (with chronic use)
Precautions
LEGAL WARNING: Extra-label use in food animals is strictly prohibited by federal law due to severe human toxicity risks.
- Cardiovascular Risk: Use with extreme caution in horses with preexisting cardiac disease; tachycardia is a common side effect.
- Pregnancy: Antagonizes oxytocin and prostaglandin F2alpha. Can diminish normal uterine contractility and induce abortion. Do not use in late-term pregnant mares unless specifically managing dystocia.
- Performance Horses: Designated as an ARCI Class 3 Drug. Use is prohibited or highly regulated by racing and show associations.
- Drug Diversion: Be highly alert for clients attempting to obtain this medication for illicit human use (bodybuilding/weight loss).
Drug interactions
May predispose the patient to ventricular arrhythmias, particularly with preexisting cardiac disease.
May antagonize clenbuterol's bronchodilating and tocolytic effects.
May increase the risk of cardiac arrhythmias.
Clenbuterol may antagonize the ecbolic effects of dinoprost.
Clenbuterol may antagonize the uterine contracting effects of oxytocin.
Concomitant administration may enhance the adverse cardiovascular and neurologic effects of clenbuterol.
May potentiate the vascular effects of clenbuterol.
Monitoring
- Clinical efficacy (improvement in respiratory rate, effort, and reduction of cough)
- Heart rate and rhythm (monitor for tachycardia or arrhythmias)
- Signs of muscle tremors, sweating, or restlessness
- Creatine kinase (CK) levels if myopathy is suspected
Pharmacokinetics
Half-life
Absorption
Peak plasma levels occur 2 hours after oral administration in horses.
Distribution
Volume of distribution is approximately 1.6 L/kg after multiple oral doses.
Metabolism
Hepatic metabolism; specific pathways not detailed, but systemic clearance is reported as 94 mL/kg/hr.
Elimination
Primarily renal. Urinary concentrations are approximately 100X those found in plasma and can persist at quantifiable levels for 288 hours (12 days) after the last oral dose.
Overdose
Overdoses can cause severe sympathomimetic toxicity (extreme tachycardia, arrhythmias, severe muscle tremors, hypertension followed by hypotension, and hypokalemia).
Treatment:
- Decontamination: Emptying the gut (gastric lavage/activated charcoal) may be appropriate depending on the dosage and timing of ingestion.
- Medical Management: Provide supportive therapy. Administration of parenteral beta-blockers (e.g., propranolol, esmolol) may be considered to control heart rate, rhythm, and elevated blood pressure.
Available products
Formulations
- Oral Syrup
- Injection (Not commercially available in the USA)
Veterinary
- Clenbuterol HCl Oral Syrup: 72.5 micrograms/mL in 100 mL, 330 mL, 460 mL bottles (Ventipulmin Syrup, Aeropulmin Syrup)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store the commercially available syrup at room temperature and avoid freezing. Always replace the safety cap on the bottle securely when not in use.
Client information
Important Information for Horse Owners
- Purpose: Clenbuterol is used to help open the airways in horses suffering from respiratory conditions like "heaves" (Recurrent Airway Obstruction).
- Side Effects: You may notice your horse sweating, acting restless, or having muscle tremors, especially when starting the medication. Their heart rate may also increase. Contact your veterinarian if these signs are severe or persistent.
- Competition Rules: This drug is strictly regulated or prohibited by many equine racing and show associations. Check with your specific organization regarding withdrawal times before competing.
- Human Safety Warning: Keep this medication strictly out of reach of children and unauthorized individuals. Clenbuterol is sometimes illegally abused by humans for bodybuilding or weight loss, which can lead to severe, life-threatening heart issues.
- Food Animal Ban: Never give this medication to animals intended for human consumption (cattle, pigs, sheep, etc.). It is illegal and causes severe poisoning in humans who eat the meat.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.