Beta-blockers are drugs taken to block the action of a chemical produced in the body (a neurochemical) called noradrenaline. It is most commonly taken as a prescription medication by patients with heart problems. By binding to beta-1 or beta-2 receptors in arteries and in the heart muscle, the normal binding of noradrenaline to the same receptors is prevented, or blocked. This slows down or blocks completely the noradrenaline-induced transmission of messages between nerves and muscles or between different nerves.

As a result of injesting beta-blockers, arteries become wider. This is beneficial particularly if an individual has a heart problem, since the heart's demand for oxygen and blood is reduced and does not have to work as hard to pump blood through the body. As well, artery dilation can relieve chest pain (angina), irregular heartbeat, glaucoma, lessen the occurrence of migraines, and even reduce nerve-inducing muscle twitches and shaking.

The calming effect of beta-blockers on muscle action has made the drugs a popular, though illegal, choice of some athletes whose performance depends on balance (such as gymnastics) or a steady hand (archery, shooting, and biathalon).

Because an athlete will tend to use beta-blockers at the same dose that is used for genuine therapeutic use, the drug will not be detected in suspiciously large quantities. It is at that point that an athlete's past history becomes important. If an athlete has no history of heart trouble or migraines, for example, the presence of a beta-blocker in submitted urine or blood samples may be cause for suspicion.

Beta-blockers can be taken orally in the forms of tablets or capsules, an injection, or as eye drops in the case of glaucoma medication. A variety of different beta-blockers are available by prescription. Examples include: acebutolol, atenolol, celiprolol, levobunolol, pindolol, and timolol.

Some beta-blockers are designed to be selective; they block beta-1 receptors more than beta-2 receptors. Beta-1 receptors are involved in heart rate and beat strength. Nonselective beta-blockers block both the beta-1 and beta-2 receptors; the latter are important in the function of smooth muscles such as the heart.

Athletics who seek the illegal benefits of beta-blockers will likely experience side effects that include drowsiness or fatigue, reduced circulation through the hands and feet, dizziness, and a dry mouth. Some of these effects detract from athletic performance. Rarely, more serious side effects, including memory loss and impotence, can result.

SEE ALSO Archery; Beta-2 agonists; Biathlon; Biofeedback; Gymnastics; Shooting.