Pharmaceuticals/Chemicals Human clinical data

Clenbuterol (Oral)

Clen

26.6 hours

Half-life

20–120 mcg

Typical dose

Community: 2 weeks on / 2 weeks off

Cycle length

β2-agonist bronchodilator used off-label for fat loss; cardiac stimulation risk.

Key takeaways

Long-acting β2 agonist, never approved for US human use; taken off-label for fat loss.
~27-hour half-life and ~90% oral bioavailability — once-daily dosing, gradual accumulation.
WADA-prohibited with a zero threshold; detectable 7–14 days after use.
Documented human harms: tachycardia, tremor, hypokalemia, rare arrhythmia and cardiac injury.

🚧 Expanded guide coming soon. This compound has PK data and a source — a full overview, mechanism, and dosing guide is pending editorial review.

Reported dosing protocols

Protocols reported in research literature and clinic/community use — informational context, not a dosing recommendation.

Use case	Dose	Route	Frequency	Duration
Bronchodilation (clinical, non-US)	20–40 mcg	Oral	Once or twice daily	As prescribed
Fat loss (community)	20 mcg start, titrated toward 80–120 mcg	Oral	Once daily	2 weeks on / 2 off

Pharmacokinetic summary

Model tier: Advanced (t½ + Cmax + Tmax + F)
Half-life: 26.6 hours
Cmax: 0.333 ng/mL
Tmax: 0.1 days
Bioavailability: 90%
Typical dose: 0.02–0.12 mg

Harm reduction

Aromatizes: No
Hepatotoxicity: mild

⚠ Clenbuterol + tadalafil compounds cardiovascular/tachycardia risk.

Frequently asked questions

Is clenbuterol a steroid?

No. It's a beta-2 adrenergic agonist, a stimulant-class bronchodilator. It shows up in steroid-adjacent contexts because of its fat-loss and mild anti-catabolic reputation, but it has no androgen-receptor activity.

Why do people cycle clenbuterol two weeks on, two off?

Beta-2 receptors downregulate with continuous exposure, so the thermogenic effect fades within weeks. The community on/off pattern attempts to restore sensitivity, though whether it actually does is untested in humans.

How dangerous is clenbuterol really?

Documented cases include arrhythmia, myocardial injury, and severe hypokalemia, usually at high or escalating doses. It has a narrow safety margin for a fat-loss agent, and combining it with other stimulants compounds the cardiovascular risk.

References

PMC clenbuterol PK
Ambroxol/clenbuterol tablet PK in healthy volunteers (Int J Clin Exp Med 2015) — Human PK data behind the dataset half-life and absorption values.

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