Alpha-adrenergic blockers are drugs used to lower blood pressure. They work by relaxing the muscles in the walls of blood vessels. With blood vessels open and relaxed, blood flow improves and blood pressure lowers. Alpha-adrenergic blockers also lower blood pressure and reduce stress on the heart by slowing the heart rhythm and lessening the force of the heartbeat. These drugs are also called alpha blockers, alpha-adrenergic antagonists and alpha-adrenergic blocking agents.