Clenbuterol
Clenbuterol is a long-acting beta-2 adrenergic agonist licensed in some countries as a bronchodilator (mainly veterinary) but widely used off-label for fat loss and physique purposes. It modestly raises metabolic rate and has mild anti-catabolic effects, at the cost of pronounced sympathomimetic side effects and evidence of cardiac hypertrophy with sustained use.
01 Overview
Clenbuterol stimulates beta-2 adrenergic receptors, producing bronchodilation and a small increase in thermogenesis and lipolysis. Its long half-life makes its stimulant effects persistent through the day. In humans it is used off-label as a fat-loss agent; in livestock it has been misused as a repartitioning agent, leading to food-poisoning outbreaks and bans on use in food animals.
Human efficacy data for fat loss are limited and much of the evidence comes from animal studies and anecdote. The muscle-sparing and hypertrophic effects seen in animals occur at doses far higher than tolerable in humans. Clinically relevant harms include tachycardia, tremor, electrolyte disturbance and, with chronic use, cardiac hypertrophy and arrhythmia risk.
02 Mechanism
Selective beta-2 adrenergic agonist. Increases cyclic AMP in target tissues, driving bronchodilation, a modest rise in resting metabolic rate and lipolysis, plus beta-mediated cardiac and skeletal-muscle effects.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Starting | 20–40 mcg/day | Oral | Low starting dose to assess tolerance. |
| Common | 40–80 mcg/day | Oral | Typical off-label fat-loss range, often titrated upward. |
| Heavy | 100–140 mcg/day | Oral | High end associated with pronounced tremor, tachycardia and cardiac strain. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Increased metabolic rateSmall increase in resting energy expenditure and fat oxidation. | modest thermogenic rise | Observational | |
| Anti-catabolic / muscle sparingPronounced muscle preservation in animal models; human effect is far smaller at tolerable doses. | marked in animals, minor in humans | Preclinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| Tachycardia and palpitationsElevated heart rate and palpitations from beta-adrenergic stimulation. | Moderate | Nearly universal at active doses | Observational | |
| Tremor and anxietyFine hand tremor, jitteriness and restlessness. | Mild | Very common | Observational | |
| Muscle crampsCramping linked to taurine and electrolyte depletion. | Mild | Common | Observational | |
| Cardiac hypertrophySustained beta stimulation is associated with cardiac hypertrophy and increased arrhythmia risk; well documented in animals and a concern in chronic human use. | Severe | With sustained use | Preclinical |
06 Commonly used with
What clenbuterol is combined with, and why. This is about intent rather than safety — the interactions table below covers what is dangerous. Nothing here is listed without what it costs.
| Compound | Frequency | Purpose & trade-off |
|---|---|---|
| Stacked compounds | ||
| LiothyronineT3) (clen/T3 | The classic clen/T3 fat-loss stack, combining beta-agonist thermogenesis with elevated thyroid metabolic rate.Trade-off: The pairing raises heart rate and cardiac strain while T3 accelerates muscle loss on a deficit. | |
| Testosteronemuscle sparing | Run in a cut so an anabolic base preserves lean mass while clenbuterol drives fat loss.Trade-off: Adds androgenic and suppressive burden on top of clenbuterol's cardiovascular stress. | |
| Yohimbinestubborn fat | Layered in fasted to target stubborn alpha-2 adrenergic fat stores alongside clenbuterol's beta stimulation.Trade-off: Stacking two stimulants sharply raises heart rate, blood pressure and anxiety risk. | |
| Support & ancillaries | ||
| Ketotifenreceptor resensitising | Added to upregulate beta-receptors so clenbuterol keeps working without constant dose escalation.Trade-off: Ketotifen is strongly sedating and its appetite stimulation can undercut a cutting diet. | |