Ephedrine is the main bioactive alkaloid found in plants of the genus Ephedra (Ephedra sinica, Ephedra intermedia, Ephedra equisetina). Pseudoephedrine is the synthetic version of ephedrine. Both are structurally related to amphetamine and both possess amphetamine-like effects. The Chinese have used Ephedra medicinally for over 5,000 years and Ephedra, also called Ma Huang is used in many herbal products aimed at weight loss and energy enhancement. While its main active constituent, ephedrine, was isolated in 1887, the herb did not become popular with US physicians for its bronchodilating and decongesting properties until the 1920’s. Recently, drugs with better activity and fewer side effects are more commonly used for these purposes. Both ephedrine and its synthetic counterpart stimulate the central nervous system, dilate the bronchial tubes, elevate blood pressure and increase heart rate. However, it is the weight loss properties of ephedrine that make it of particular interest because it appears to provide long term increases in energy expenditure.
Animal studies provide rigorously controlled conditions that allow accurate assessment of the effects of the ephedrine. Such studies to date generally show that ephedrine is an effective weight loss agent because it causes increases in energy expenditure. For example in one study1, researchers assessed the thermogenic properties of methylxanthines and ephedrine in rodents. In initial experiments researchers fed obese mice caffeine and theophylline for 6 weeks at doses of 1.36 and 2.27 grams per kg body weight, respectively. The results showed that body weight remained constant in both the control and treatment groups, suggesting that the methylxanthines did not cause weight loss at the doses administered. In contrast, treatment with ephedrine at a dose of 1.0 gram per kg body weight alone cause weight loss of 14% of body weight during the same 6 week period, 42% of which was body fat. The weight loss seen with ephedrine was likely due to a 10% increase in energy expenditure recorded in the mice fed ephedrine.
These results suggest that ephedrine has a thermogenic effect that is significantly greater than that of caffeine or theophylline. However, when ephedrine is combined with methylxanthines, it appears that the effects on fat loss are accentuated. For example, in the same study, the researchers administered a combination of either ephedrine, caffeine and theophylline (at 1.0, 1.36 and 2.27 grams per kg body weight, respectively), ephedrine and caffeine (at 1.0 and 3.63 grams per kg body weight, respectively) or ephedrine and theophylline (at 1.0 and 3.63 grams per kg body weight, respectively) to the mice. This increased energy expenditure a further 10% above the value measured following administration of ephedrine alone and caused a 25% reduction in body weight. Of this reduction in body weight around 75% was body fat. There was no difference in weight loss between the different methylxanthines treatments suggesting that both caffeine and theophylline are equally effective at accentuating the effects of ephedrine.
Following the 6 week administration of ephedrine food intake was unaltered, suggesting that the weight loss was not due to calorie restriction. In fact although ephedrine caused a 6% reduction in food intake when administered alone for the initial 2 weeks, following this period food intake increased to compensate for the initial anorectic effect. Likewise, the combination treatments also caused an initial reduction in food intake of around 15 to 23 % but there was a compensatory increase over the next two weeks. Therefore after 4 weeks of combination treatment, food intake of the control and treatment groups was similar, but the treatment group had lost 25% body weight. This adds further proof that colories restiction in not necessary to cause weight loss. Taken as a whole, these results further support a role for ephedrine as an effective weight loss drug in mammals. However, this weight loss is not caused by energy restriction, but likely through stimulation of the adrenergic receptors of the sympathetic nervous system.
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