What are beta blockers and how do they work?

Beta blockers, also known as beta-adrenergic blocking agents, are drugs that block norepinephrine and epinephrine (adrenaline) from binding to beta receptors on nerves. Norepinephrine and epinephrine are produced by nerves throughout the body as well as by the adrenal gland. They serve as neurotransmitters (chemicals that nerves use to communicate with one another) that may be active locally where they are produced, or elsewhere in the body, when they are released into the blood. There are both alpha and beta receptors in the body. There are three types of beta receptors and they control several different functions based on their location in the body.

beta-1 (β1) receptors are located in the heart, eye, and kidneys. beta (β2) receptors are found in the lungs, gastrointestinal tract, liver, uterus, blood vessels, and skeletal muscle. beta (β3) receptors are located in fat cells.

Beta blockers primarily block β1 and β2 receptors and thereby the effects of norepinephrine and epinephrine. By blocking the effects of norepinephrine and epinephrine, beta blockers reduce heart rate; reduce blood pressure by dilating blood vessels; and may constrict air passages by stimulating the muscles that surround the air passages to contract considered an adverse side effect).