sympatholytic
A sympatholytic is a drug that turns down the sympathetic nervous system, the opposite of a sympathomimetic. If a sympathomimetic presses the accelerator, a sympatholytic eases off it, slowing the heart, relaxing vessels, and lowering blood pressure.
There are several ways to achieve this. Receptor antagonists block adrenergic receptors directly: beta blockers occupy beta receptors, and alpha blockers occupy alpha-1 receptors. Centrally acting agents such as clonidine reduce sympathetic outflow from the brainstem through alpha-2 receptors. Adrenergic neuron blockers prevent norepinephrine from being released in the first place.
Because excess sympathetic activity drives high blood pressure and overworks the heart, sympatholytics are workhorses of cardiovascular medicine, used in hypertension, angina, certain arrhythmias, and heart failure. Common trade-offs include fatigue, slow heart rate, and a drop in blood pressure on standing.
Doxazosin, an alpha-1 blocker, is a sympatholytic that lowers blood pressure by relaxing the smooth muscle in artery walls.
An alpha-blocker used for blood pressure.
Abruptly stopping a long-used sympatholytic such as a beta blocker or clonidine can trigger rebound: the body, having up-regulated, suddenly faces unopposed sympathetic activity, causing a surge in heart rate and blood pressure.