As potentially performance-enhancing substances, beta-2 agonists are on the list of prohibited substances. Beta-2 agonists are contained in asthma medications. They improve breathing by widening the bronchi in the lungs. They can be administered orally or by inhalation. In high doses, they also stimulate muscle growth.
Beta-2 agonists are prohibited under the Prohibited List. The best-known members of this substance class are clenbuterol, formoterol and salbutamol. During the past few years, some of the rules on the prohibited beta-2 agonists on the Prohibited List have been gradually relaxed. As a result, the beta-2 agonists commonly used in asthma inhalers are permitted provided that a certain threshold is not exceeded.
Asthma and Sport
Asthma is a chronic inflammation of the mucosa of the airways. Normally, about five to ten percent of all people suffer from this disorder. To treat the condition, they use asthma inhalers containing beta-2 agonists. Among elite athletes, light to moderate deficits in bronchial function are diagnosed noticeably more often than in the average population As a result, sports doctors in the past (approx. 1990 – 2006) often prescribed asthma medications to athletes. By contrast, non-asthmatic people do not benefit from asthma medications, they only suffer from their side effects. Asthma medications are therefore now no longer used by athletes across the board.
Because they promote protein synthesis, beta-2 agonists in high doses have a muscle-building (anabolic), and simultaneously, a fat-reducing effect. That is why doping athletes use them as an alternative to anabolics. In some countries, beta-2 agonists are also used illegally as growth-promoting drugs in animal fattening (e.g. clenbuterol). In Switzerland, only a few veterinary medications for the treatment of respiratory disorders contain clenbuterol. It is not used in human medicine.
Effect of beta-2 agonists
Adrenaline and noradrenaline act via specific receptors (alpha-1, alpha-2 and beta-1, beta-2) located in various tissues including skeletal muscle and fat. Beta-2 agonists are substances that stimulate the beta-2-adrenergic receptors and thus mimic the effect of adrenaline and noradrenaline. By this mechanism, beta-2 agonists relax the bronchial muscles and widen the airways, allowing more oxygen to reach the lung. When administered in high doses, beta-2 agonists have a muscle-building (anabolic), and simultaneously, a fat-reducing effect.
Inhaled beta-2 agonists affect mainly the smooth musculature of the airways.
They stimulate beta-2-adrenergic receptors in the bronchi and thus cause the bronchial muscles to relax.
When administered in high doses, beta-2 agonists have a muscle-building (anabolic) effect on the skeletal muscles and reduce body fat.
⬆ Bronchial widening
⬆ Skeletal muscle growth
⬆ Body fat reduction
Side effects and consequences of beta-2 agonist abuse
Adverse effects include excessive sweating, restlessness, uncontrollable muscle trembling (tremor) and a racing heart (tachycardia). These effects are due to the additional, unspecific activation of beta-1 receptors in other organs than the lung.
Beta-2 agonists are dangerous to the heart
Increased oxygen consumption when the heart rate is accelerated can lead to an inadequate oxygen supply of the heart muscle cells. This may cause angina pectoris (sudden chest pain due to impaired blood flow in the heart). Another possible adverse effect is a decline in the blood potassium level, which may in some cases lead to heart rate irregularities (arrhythmias).
Increased glucose levels
An rise in glucose levels due to increased glycogen breakdown in the liver can occur.
Beta-2 agonists are used particularly in endurance sports such as cycling, swimming, cross-country skiing and athletics. In these disciplines, a high oxygen supply is especially useful. By widening the airways with beta-2 agonists contained in asthma inhalers, athletes attempt to supply the lung with more oxygen. However, recent studies have not provided clear evidence of such an effect. To the contrary, non-asthmatic persons only suffer the adverse effects of these medications.
Substitute for anabolics
Due to their muscle-building (anabolic) and fat-reducing effect at high doses, beta-2 agonists can be abused in virtually all sports. Due to these effects, they are widely used in the body building scene. They serve as a substitute for anabolics because they lack their negative, sex-specific (androgenic) side effects.