OnePin Peptide Library · Metabolic
Clenbuterol (Clen)
Clen · Clenbuterol HCl
Clenbuterol is a long-acting beta-2 adrenergic receptor agonist originally developed as a bronchodilator for the treatment of reversible airway obstruction (asthma, chronic obstructive pulmonary disease). It has been approved for human respiratory use in several countries (for example certain European, Latin American, and Asian markets) under brand names such as Spiropent, Ventipulmin, and Broncodil. In the United States it is not FDA-approved for human use; it is used in veterinary medicine as a bronchodilator in horses and is prohibited in food-producing animals.
Take in the morning given the ~36 hour half-life - evening dosing disrupts sleep for most users. Start at 20 mcg/day and increase gradually every 2-3 days, monitoring resting heart rate, blood pressure, and tremor. Classic cycling is 2 weeks on / 2 weeks off to limit beta-2 desensitization. Supplement potassium and taurine to offset hypokalemia and muscle cramps.
Start here. Every protocol below is ordered lowest-first. Begin at the smallest effective dose, hold about a week to assess tolerance, and step up only if needed.
How it works
Clenbuterol is a selective beta-2 adrenergic receptor agonist. Stimulation of beta-2 receptors on bronchial smooth muscle produces relaxation and bronchodilation, which is the basis for its approved respiratory use. The same receptor agonism in adipose tissue activates hormone-sensitive lipase via the cAMP / PKA pathway, driving lipolysis, and stimulation of beta-2 receptors in skeletal muscle produces a modest anti-catabolic and anabolic-sparing effect in animal models.
Clenbuterol is a selective beta-2 adrenergic receptor agonist. Stimulation of beta-2 receptors on bronchial smooth muscle produces relaxation and bronchodilation, which is the basis for its approved respiratory use. The same receptor agonism in adipose tissue activates hormone-sensitive lipase via the cAMP / PKA pathway, driving lipolysis, and stimulation of beta-2 receptors in skeletal muscle produces a modest anti-catabolic and anabolic-sparing effect in animal models.
Thermogenesis is driven by increased metabolic rate, elevated body temperature, and increased oxygen consumption - typical effects of sympathetic activation. Because of clenbuterol's very long half-life (approximately 36 hours) and tissue accumulation, effects persist well beyond each dose, and beta-2 receptor desensitization develops within 2-3 weeks of continuous use, which is why intermittent dosing schedules (2 weeks on / 2 weeks off, or similar) are common.
At higher doses, cardiac beta-1 and beta-2 agonism causes tachycardia, increased contractility, and can produce cardiac hypertrophy and arrhythmia risk with prolonged use. Electrolyte disturbances (notably hypokalemia) are characteristic of beta-2 agonist overuse.
What to expect
First 1-3 days: elevated resting heart rate, hand tremor, sweating, and sleep disturbance. Thermogenic sensation (warmth) is typically noticeable within 30-60 minutes of the first dose.
Week 1-2: measurable fat loss under an appropriate caloric deficit, often with preserved strength output. Tremor usually subsides as tolerance builds. Muscle cramps are common without potassium/taurine supplementation.
Week 2 onward: receptor desensitization begins to blunt the thermogenic effect. The 2-weeks-off phase restores sensitivity. Extending continuous use beyond 3-4 weeks without a break compounds cardiac risk for diminishing returns.
Evidence
Interactions & stacking
What's safe to combine, and what belongs in a separate pin.
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Side effects & safety
Commonly reported
- Tachycardia / elevated resting heart rate
- Hand tremor (especially first few days)
- Sweating and elevated body temperature
- Sleep disturbance (especially if taken late in the day)
- Muscle cramps (hypokalemia / electrolyte loss)
- Anxiety, jitteriness, headache
Less common & notes
- Palpitations, atrial or ventricular arrhythmia, chest pain, sustained hypertension, nausea, vomiting.
- Rare but serious: myocardial infarction, cardiac hypertrophy with prolonged use, sudden cardiac death at supratherapeutic doses.
- Hypokalemia can produce muscle weakness and ECG changes.
- Case reports of clenbuterol poisoning from adulterated supplements or contaminated meat have produced hospitalizations for tachyarrhythmia and electrolyte disturbance.
Pharmacokinetics
Storage. Store at controlled room temperature (20-25°C / 68-77°F). Protect from moisture and light. Keep in original container with desiccant when available. Shelf life typically 2-3 years from manufacture date. Keep out of reach of children - overdose risk is high because of the very long half-life.
Regulatory status
Not FDA-approved for human use in the United States. Approved for veterinary use in horses (brand name Ventipulmin) and prohibited in food-producing animals under FDA regulation. Approved for human respiratory indications in several European, Latin American, and Asian markets under brands including Spiropent, Broncodil, and Ventipulmin. Classified as a prohibited substance at all times (in and out of competition) by the World Anti-Doping Agency (WADA), USADA, NCAA, and most other sporting bodies.
Put it to work
Calculate, log & track
Open Clenbuterol (Clen) straight into OnePin with your vial and dose pre-filled, then let it handle the syringe math and remind you before the vial runs out.
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The guide & community
The complete Clenbuterol (Clen) walkthrough, real protocol discussion and coaching live inside the BlessUp community on Skool.
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