Clen: Highly Effective Cutting Compound

TL:DR It’s original purpose, in short, is that it makes breathing easier: good for folks with asthma or other chronic lung illness. It’s no longer used for this purpose in the west, but it lives on as a popular cutting agent. It is relatively high risk when compared to compounds that are of similar popularity, but can be utilized for those not running high doses for long periods of time and/or prone to high blood pressure.

What Is It?

A bronchodilator - it increases airflow to the lungs. It is classified as a Beta2 adrenergic receptor agonist. For those interested in how Beta2 agonists work, the Wiki article offers a good summary:

Activation of β adrenergic receptors leads to relaxation of smooth muscle in the lung, and dilation and opening of the airways. β adrenergic receptors are coupled to a stimulatory G protein of adenylyl cyclase. This enzyme produces the second messenger cyclic adenosine monophosphate (cAMP). In the lung, cAMP decreases calcium concentrations within cells and activates protein kinase A. Both of these changes, inactivate myosin light-chain kinase and activate myosin light-chain phosphatase. In addition, β2 agonists open large conductance calcium-activated potassium channels and thereby tend to hyperpolarize airway smooth muscle cells. The combination of decreased intracellular calcium, increased membrane potassium conductance, and decreased myosin light chain kinase activity leads to smooth muscle relaxation and bronchodilation.

Study 1: 1, 2.5 and 5 µg/day in an n=6, with no side effects noticed, nor any significant improvement in ‘bronchial resistance’, which I’ll take to mean it was ineffective at that dose in making it easier to breathe.

Study 2: Two groups with different chronic diseases trialled clen doses at placebo, 1, 2.5, 5, 10, 20, 25 and 30µg. At 1 and 2.5, there were no differences to placebo, but improvements in capacity were present at the higher doses. There were not adverse effects below 5µg, with the minimum effective doses were 5-10µg.

Study 3: At higher doses, children who consumed between 0.05-0.075 mg of clenbuterol showed only mild tachycardia, and a 30-year-old woman who consumed 30 tablets (equivalent to 0.6 mg clenbuterol or 10 µg/kg) developed tachycardia and slight hypertension shortly after consumption. After intervention, pulse rate and blood pressure returned to normal.

Study 4: n=100 took doses of 20-60 µg/day (0.3-1.0 µg/kg bw per day) for up to 1 year or 20 µg/day (0.3 µg/kg bw per day) for up to 6 months and showed no adverse effects except for slight tremor and occasional, mild tachycardia. When you look at the chronic breathing diseases they were being treated for, the ability to breathe was an agreeable trade off for occasional irregular heartbeats.

It is somewhat liver toxic, established in mice and rats, though less so in higher order mammals. At higher doses myocardial necrosis was present aka a heart attack. I’m not clear on what dose caused this but it remains a possibility.

It will however, act in a very muscle sparing way, inhibiting the effects on protein degradation, and is highly specific to muscle. In rats, clen substantially increased the weight of skeletal muscle from 19% of 35% (presumably that’s a percentage of total body weight), while reducing fat content by 32% in the 12 month old group. A separate and frankly horrific study that involved burning rats alive and then using clen as a recovery compound found that energy expenditure went up when at rest, which besides its muscle sparing qualities is the other reason clen is popular - no change to a diet that would otherwise have you at a steady weight is necessary to lose fat.

Doses & Cycles

The PEDsDB (not mobile friendly, sorry) has recommended starting dose as 20 µg/day.

Side effects that required hospitalization included tachycardia, widened pulse pressure, tachypnea, hypokalemia, hyperglycemia, elevated creatine phosphokinase, palpitations, chest pain, and tremor. Treatment is activated charcoal (activated almonds, anyone?), benzos, beta blockers, potassium replacement and IV. These are the exceptions, not the rule, and are likely indicative of either long term abuse or high dose.

Given the results of study 4 (above), 20-60 µg/day is relatively safe with side effects of tremors and mild tachycardia. Short term use for our benefits at these doses can be undertaken. However, I would not recommend this compound for anyone prone to high blood pressure or cardiac disease, which clen is not exactly going to help with.


I am highly wary of clen given my aversion to compounds that have an impact on cardio health (he says after injecting tren). My double standards aside, clen is extremely popular as a cutting agent and commonly found. Side effects of tremors and irregular heartbeat is to be expected at any dose over 5mcg / day, but studies have shown it tolerable as do anecdotes. Exercise (heh) caution in running doses > 60mcg / day