Study on Clenbuterol and Heart Disease
from Muscular Development, Dan Gwartney, MD, Invalid Link Removed
Bodybuilders and other athletes have long sought an effective pharmaceutical means of shedding body fat. Historically, three agents have been most highly regarded as fat-burning drugs; they are clenbuterol, Cytomel (T3) and dinitrophenol (DNP). Of these three, only Cytomel is clinically used in the United States, and only for rare conditions of thyroid disease, not as a weight loss agent. All three of these drugs have been shown to have dangerous side effects.
Potential for Harm
The most widely abused of the three drugs is clenbuterol. In part, this is due to the report that clenbuterol is anabolic in animals, as well as a potent fat-burner, though the anabolic effect seems to be minimal or absent in humans.1 While clenbuterol is used by many athletes, it has found favor with female athletes and entertainers because it is not androgenic, and will therefore not cause the unwanted side effects seen with steroid abuse.2
Most experienced users of clenbuterol realize it is a drug with limited effect, and they schedule its use for brief periods, typically using a two-days-on/ two-days-off cycle. This on-and-off schedule is necessary, as clenbuterol causes a rapid down-regulation of the receptors that are responsible for its actions.3 In other words, clenbuterol will quickly "burn out" the cells and stop working with prolonged use.
However, as use of clenbuterol spreads, less knowledgeable users gain access to the drug, and "inappropriate" use becomes common. The problem is magnified by the fact that clenbuterol users obtain the drug from illicit, black market sources and do not seek professional advice regarding its use, risks or side effects. The risk of harm is greatly increased when the drug is used indiscriminately, or for prolonged periods.
Most of the safety data on clenbuterol has been obtained using animal studies, due in part to its high-risk profile. There are published reports of humans suffering serious consequences with clenbuterol abuse, including overdose and heart attack, but these effects are primarily related to short-term exposure.4,5
A Study of Horses
Recently, a study was published based on an investigation of chronic (long-term) use of clenbuterol and its effect on heart function in exercising horses.6 The horse may not seem like a good comparison to humans for issues like drug abuse, but in actuality, the horse is an excellent model to use when investigating effects related to exercise.
This study was designed to evaluate any effects of clenbuterol, given five days per week, on the heart size or function of exercising horses. The horses used a treadmill at various speeds for 20 minutes a day, three days per week, and the hearts were examined by echocardiography, which allows the heart to be viewed and measured on a monitor.
The investigators discovered that after eight weeks of clenbuterol treatment, the hearts of the horses had undergone structural changes, which made them work less efficiently and also made them more prone to certain heart problems. These changes were only evident immediately following exercise, when the heart was working harder, but the authors of the study felt that the changes might have become more apparent after a longer treatment period. The data from the study also showed that the VO2 max of the clenbuterol treated horses was lower, suggesting that they would become more easily fatigued and have a lower exercise tolerance.
Sadly, the study did not collect data on changes in blood pressure in the animals, leaving some of the results open to interpretation. Previous animal studies, predominantly on mice and rats, have shown significant changes in heart size, with the heart muscle hypertrophy keeping pace with the anabolic effect on other muscles.7,8 There is some contention as to whether this change in heart size affects function and if it is "negative" growth (pathologic) versus positive growth (physiologic). Several of the studies have determined through measures of RNA, protein content or enzyme levels that the change is physiologic, or a "good" growth. However, none of these studies have shown improved cardiovascular performance as a consequence of the clenbuterol induced changes.9