Formoterol is a beta-2 agonist used in the management of asthma and chronic obstructive pulmonary disease. A beta-2 agonist is a compound that stimulates beta-2 receptors, with little or no effect at the beta-1 receptors. While such products were traditionally used for the treatment of bronchial ailments, the use of beta-2 agonists (e.g., clenbuterol) in the livestock industry revealed some interesting side effects, namely increased skeletal muscle mass and a concominant decrease in body fat.

In a recent rat study published in The British Journal of Pharmacology, the investigators examined how beta-2 agonists, formoterol and salmeterol, affect skeletal and heart muscle mass. Both drugs were administered via daily i.p. injection at different doses (ranging from 1 to 2,000 micrograms per kilogram of body mass per day) for four weeks. The results revealed that formoterol was more potent than salmeterol. In fact, doses as low as 1 microgram per kilogram per day of formoterol can elicit significant skeletal muscle hypertrophy with minimal heart muscle hypertrophy. However, well-controlled human studies are needed before firm conclusions can be drawn. The potential side effects of beta-2 agonists include anxiety, fast heart rate and low blood potassium.

Reference: Ryall JG et al. Systemic administration of beta-2-adrenoceptor agonists, formoterol and salmeterol, elicit skeletal muscle hypertrophy in rats at micromolar doses. Br J Pharmacol, 2006;147:587-95.

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About Anssi Manninen

Anssi Manninen holds an MHS in sports medicine from the University of Kuopio Medical School. His numerous cutting-edge articles in MD firmly establish his reputation as a leading authority on hardcore sports nutrition. Anssi´s articles have also been published in scientific journals, including The British Journal of Sports Medicine, The Journal of International Society of Sports Nutrition, Metabolic Syndrome and Related Disorders, Nutrition & Metabolism, and Journal of Sports Science and Medicine. Anssi is also an associate editor for Nutrition & Metabolism, a leading scientific journal in the area of nutritional biochemistry.