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Clenbuterol is an adrenergic stimulant and has been available for use as a bronchodilator in Europe since 1977. It is distributed as tablets, solutions, drops and syrups.(4) Typically used in aerosolized, inhaled form to reverse bronchial constriction.(6) Clenbuterol is banned for both animal and human use in the United States.(5) It is banned by the USOC and IOC. The USOC bans the use of all beta 2 agonists other than those approved for used in medical treatment of asthma. It is used in the livestock industry to increase lean muscle mass while retarding adipose tissue deposition in growing animals.(6)

Athletes are using clenbuterol to help build muscle. Its use resulted in expulsion of Jud Logan, hammer thrower and Bonnie Dasse, shot-putter from the 1992 Summer Olympic Games.(5)

Drugs that simultaneously increase lean muscle and retard fat deposition are being referred to as repartitioning agents.(6) It appears that clenbuterol is able to induce a muscular growth response which is true hypertrophy.(4) It exerts two distinct effects in which athletes are interested. It increases the rate of muscle protein deposition and promotes lipolysis. Apparently, clenbuterol suppresses protein degradation more than it enhances synthesis of protein. In rats, it has caused hypertrophy, not hyperplasia, of skeletal and cardiac muscle.(6)

Animal studies on clenbuterol have shown a significant muscle building effect. Some animal studies suggest that clenbuterol may have legitimate therapeutic uses in the treatment of muscle wasting disorders.(4) A rat study published in 1996 suggested an increase in muscle mass due to hypertrophy (increase in myofibrillar protein). Force generating ability increased, but force/gram of muscle was unchanged. "The finding that clenbuterol hastens fatigue during short-term, intense muscle contractions implies that beta-agonists may not be appropriate for some conditions." (1) The lipolysis effect is not consistent throughout all species in which it has been tested.

(6) Studies with similar drugs on humans point to a anti-catabolic effect. This means these drugs prevent breakdown of muscle. The theory is that if the body does not break down muscle as easily, it can ultimately build more muscle.

Adverse effects include tachycardia, palpitations, nosebleeds, dizziness, nervousness, muscle aches and pains, severe headaches, alternating fever and chills, increased sensitivity to stress, irritability, violent muscle tremors, myocardial infarction, stroke and hemorrhaging. Some studies noted an increase in cancerous tumors in offspring of animals that had been administered beta agonists.(3)

Athletes take clenbuterol in capsular or tablet(20mcg) form, not by inhalation. Dosage is usually four to eight tables daily.(2) A schedule of three weeks on, three weeks off is used. During the "on" period the drug is taken for two consecutive days and discontinued for two days. Presumably this avoids some of the receptor down-regulation. It is often taken along with niacin with the idea of improving muscle blood flow and, thereby, the distribution of the drug. Some athletes take Sudafed, ephedrine or phenylpropanolamine during the two day "off" period with the hope of thwarting down-regulation.(6)

  1. Dodd, S., et. al. "Effects of clenbuterol on contractile and biochemical properties of skeletal muscle" Medicine and Science in Sport and Exercise 28(6):669-676, 1996.
  2. Duchaine, D. Underground Steroid Handbook (II) Update:1992. Daniel Duchaine: USA, pp. 31-44.
  3. Goldman, G. "Clenbuterol The Dangers of a New Growth Drug" The Professional Journal of Sports Fitness, Fall, 1992
  4. Green, G. "Clenbuterol: A new Anabolic Drug?" Sports Medicine Digest 15(8):1-2, 1993.
  5. "News Briefs" Physician and Sports Medicine 20(10):19-20, 1992
  6. Prather, I., et. al. "Clenbuterol: a substitute for anabolic steroids?" Medicine and Science in Sport and Exercise 27(8):1118-1119, 1995.