What is a Clenbuterol Cycle?

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  • Written By: Sunny Griffis
  • Edited By: Angela B.
  • Last Modified Date: 11 November 2018
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Clenbuterol, also known as clen, is a beta-2 agonist commonly used for its ability to help burn fat and build lean muscle tissue, though it tends to lose its efficacy after a few weeks. Users try to prevent this loss and stave off bad side effects by rotating their dosages, creating a clenbuterol cycle. The average length of a cycle is three weeks, although the timing varies depending on the user.

Clenbuterol cycles are tailored according to physical reactions and personal preferences. Users sometimes take an anti-histamine in conjunction with this substance to increase the fat-burning effects and prolong the cycle. Clenbuterol is approved in the United States by the Food and Drug Administration (FDA) as a bronchodilator to treat horses. Outside the U.S., it also is used to treat humans for bronchial conditions. This asthma medication stimulates beta2-adrenergic receptors and improves airway obstructions.

Some athletes and bodybuilders use this substance to accelerate fat loss and aid in building muscle. The State University of New Jersey’s study of clenbuterol therapy on horses concluded that it causes significant fat loss. When combined with exercise, subjects lost an average of more than 17% body fat in two weeks. Women athletes and physique competitors use clenbuterol as a weight-loss supplement. Female users often prefer it over other anabolic drugs because of its lack of androgenic side effects, such as facial hair and deepening of the voice.


Clenbuterol is a powerful stimulant and has some potentially severe side effects, including insomnia, tremors, headaches, night sweats, nausea, dizziness, and heart palpitations. It can also cause an increase in blood pressure, enlargement of the heart, and other cardiac complications.

Taking this substance in cycles can help to combat the side effects and to prolong desired fat loss results. Some people use it for two weeks, then break for two weeks, and then repeat until body composition goals are reached. Another recommendation by distributors is to ingest clenbuterol for two days, take two days off, and then repeat for three weeks. This clenbuterol cycle is sandwiched between a start phase and end phase designed to help the body adjust.

The FDA has not approved clenbuterol for human use in the U.S., but illicit use among athletes and bodybuilders is common because of its wide availability. This substance is available in syrup, injection and tablet form. It is considered a performance-enhancing drug and is listed as a banned substance by the International Olympic Committee and the World Anti-Doping Agency.


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