Clenbuterol is a beta 2 adrenergic receptor agonist, which is a class of drugs used in treating asthma and other pulmonary diseases. This class of drugs acts on the β2-adrenergic receptor, causing smooth muscle relaxation resulting in dilation of the bronchial passage. Side effects of this class of drugs generally include insomnia, anxiety, and tremor.
Clenbuterol is a CNS stimulant and increases thermogenisis. It will lead to a rise in blood pressure and result in a slight increase in body temperature. Below is a list of side effects:
Increase in blood pressure
Increase in body temperature
Increase in sweating
Dizziness, light headedness
Muscle cramps & muscle tremors
Various side effects have also bee documented in studies involving animals:
Treatment with Clenbuterol increased size of both slow and fast skeletal muscles, and as well as the heart muscle. 1
Clenbuterol treatment increased fatigability in Soleus and Diaphragm muscles by 30 to 40%. 2
It is reported that clenbuterol increases the lean- to fat conversion in livestock and is an illegal stimulating and growth promoter. Consumption of meat containing clenbuterol residues causes adverse health effects in human, reduces the performance in exercise and disturbs reproductive system & hormone response. 3
Treatment with clenbuterol exhibited cardiac hypertrophy where absolute heart mass increased by ~ 19% indicating strongly that chronic clenbuterol use adversely affects exercise performance in rats. 4
List of Clenbuterol Side Effects & Studies
Cardiac hypertrophy - thickening (enlarging) of the heart muscle - is a possible side effect of using clenbuterol demonstrated in animal studies. As well, there have been two reports of myocardial infarction, or heart attacks. In two unrelated cases, 2 otherwise healthy body builders aged only 26 and 17 experienced myocardial infarction from the use of Clenbuterol. Various studies have also found that prolonged use actually reduced physical performance of the subjects. See below.
The weight loss effects of this drug is well documented in animal studies. Below is one study showing clen and exercise reduced fat mass by 19.5% in horses.
Chronic administration of therapeutic levels of clenbuterol acts as a repartitioning agent. Kearns CF, McKeever KH, Malinowski K, Struck MB, Abe T. Department of Animal Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, USA.
Summary: 23 unfit standard bred mares were placed in 4 groups: clenbuterol only, clenbuterol plus exercise, exercise only, and control group. The study found the exercise only group body fat reduced by 9.3%, clenbuterol group reduced fat mass by 15.4%, and the clenbuterol and exercise group decreased fat by 17.6% while increase fat free mass by 4.4%. The results suggest that exercise with Clenbuterol reduced fat mass and chronic use caused significant repartitioning in the horses.
Year-long clenbuterol treatment of mice increases mass, but not specific force or normalized power, of skeletal muscles. Lynch GS, Hinkle RT, Faulkner JA. Institute of Gerontology, University of Michigan, Ann Arbor, USA. email@example.com
Summary: This study tested the treatment with clenbuterol on increase of skeletal muscle mass in mice. The clenbuterol group received 1.5-2mcg/kg of clen per day for 52 weeks. The study found clenb treatment increased the absolute mass of each muscle tested: the heart by 28%, extensor digitorum longus (EDL) by 16%, soleus by 22% and tibialis anterior by 17%. However absolute power output was no different between the clenbuterol group and the control group leading to the conclusion that "following year-long treatment of mice with clen, the mass of the heart and both fast and slow skeletal muscles is increased, but the lack of any change in normalized power output indicates that clenbuterol has little therapeutic effect on the functional properties of skeletal muscle."
Beneficial versus adverse effects of long-term use of clenbuterol in mdx mice. Dupont-Versteegden EE, Katz MS, McCarter RJ. Department of Physiology, University of Texas Health Science Center at San Antonio, USA.
Summary: This study involved mice fed with clenbuterol 1 - 1.5 mcg/kg body weight. Functional characteristics of soleus (SOL) and diaphragm (DIA) muscles were evaluated. The study found clenbuterol treatment was associated with a 30-40% increase in fatigability in DIA and SOL muscles of control and mdx mice at both ages. Furthermore, 1-year-old mdx mice receiving clenbuterol exhibited deformities in hind limbs and spine. These results suggest that long-term clenbuterol treatment has a positive effect on muscle growth and force generation, but has adverse side effects such as increased muscle fatigability and development of deformities.
1. Year-long clenbuterol treatment of mice increases mass, but not specific force or normalized power, of skeletal muscles.Lynch GS, Hinkle RT, Faulkner JA.
Institute of Gerontology, University of Michigan, Ann Arbor, USA.
2. Beneficial versus adverse effects of long-term use of clenbuterol in mdx mice.Dupont-Versteegden EE, Katz MS, McCarter RJ.
Department of Physiology, University of Texas Health Science Center at San Antonio, USA.
3. Zhang Y, Wu Y.
Institute of Nutrition and Food Hygiene, Chinese Academy of Preventive Medicine, Beijing 100050, China.
4. Deleterious effects of chronic clenbuterol treatment on endurance and sprint exercise performance in rats.Duncan ND, Williams DA, Lynch GS.
Department of Physiology, The University of Melbourne, Parkville, Victoria 3052, Australia.