Clenbuterol (Spiropent)

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Clenbuterol (Spiropent) is a beta-receptor agonist drug used in the treatment of asthma and in bodybuilding for the purpose of fat loss. In some instances, it can also be used to enhance performance in endurance exercise.

When to use clenbuterol​

Clenbuterol should only be used when fat loss needs to be particularly accelerated over a relatively short period of time. For example, if the need or intent is to lose only 1 lb of fat per week, then there are better means to do this than to use clenbuterol. Where fat loss efforts are already maximized or near-maximized, however, clenbuterol use can add perhaps another 1 lb per week to the rate of loss.

Dosage and cycling of clenbuterol​

The effective dose range of clenbuterol extends from 20 mcg/day as a minimum value to 40-140 mcg/day as more common values. I think it best to start at 40 mcg/day and evaluate results on an ongoing basis, increasing dose by 20 mcg at a time as necessary. Many users adjust dosage to the level where the hands begin to shake, but fat loss can be improved markedly with doses well below this point.

Clenbuterol should be cycled rather than used continuously or for prolonged periods of time, but no exact cycling pattern is necessary. Period of use is typically from 2 to 8 weeks.

Periods of use such as 2 weeks or more at doses much in excess of 40 mcg/day results in desensitization. This can be avoided by taking 1 mg ketotifen once per day, preferably prior to retiring.

As clenbuterol clears the body only slowly, a rapid cycling pattern will result in clenbuterol never clearing the system.

To enhance performance in endurance exercise, clenbuterol should be used only at low dose, such as 20 to 40 mcg before an event. Higher doses of clenbuterol may reduce performance.

Mechanism of action of clenbuterol and of similar drugs​

Clenbuterol stimulates beta-2 receptors, which in turn increases metabolic rate and enhances lipolysis. Albuterol and salbuterol are other drugs which work similarly; ephedrine also works similarly. Clenbuterol differs from these other compounds by having a long half-life, which can make it more effective for fat loss – as few would choose to take ephedrine directly before going to bed, for example – but also may be responsible for greater tendency to desensitization.


Side effects of clenbuterol​

Clenbuterol use typically gives feelings of “the jitters” and shaking of the hands. Heart rate and blood pressure may be elevated. Scientific literature gives some reason for concern that chronic use might cause cardiac hypertrophy.

The most serious of these concerns are elevated blood pressure and/or heart rate; both these value should be monitored when using clenbuterol.


Clenbuterol can be a very effective aid to fat loss. A preferred method of administration is to begin use with 40 mcg/day, and increase dosage by 20 mcg/day only as necessary, with dosage not to exceed 140 mcg/day.

Author Bill Roberts
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