Ganglionic blockers

Drugs that block nicotinic receptors in autonomic ganglia, switching off both sympathetic and parasympathetic outflow. Mainly a teaching classic today.

Updated Nov 1, 2026

What they are

The first effective antihypertensives. Because they block every autonomic ganglion, they cause many side effects and are now rarely used; mecamylamine is the one oral agent still available in some countries.

Mechanism of action

Preganglionic neurons release acetylcholine onto neuronal nicotinic receptors on the postganglionic neuron. Ganglionic blockers stop this transmission (mecamylamine by blocking the receptor's ion channel). The effect on each organ depends on which division normally dominates it: vessels are mainly sympathetic, so they dilate and blood pressure falls, especially on standing; the heart, eye, gut and bladder are mainly parasympathetic, so heart rate rises and the pupils dilate, accommodation is lost, and the gut and bladder become sluggish.

Target: Neuronal nicotinic acetylcholine receptors of autonomic ganglia

Drugs in this class

MecamylamineAn oral ganglionic blocker for severe hypertension. Blocking both autonomic divisions causes orthostatic hypotension…Neuronal nicotinic acetylcholine receptor of autonomic ganglia (channel blocker)

Others in the class

Hexamethonium (historical)
Trimethaphan (no longer marketed in the US)

Test yourself

Think of the answer, then tap the question to see it.

Why does a ganglionic blocker cause tachycardia?

The heart's resting tone is mainly parasympathetic (vagal); removing it lets the heart rate rise.

Why is the blood pressure fall worse when standing?

Sympathetic reflexes that constrict vessels on standing are blocked, so blood pools in the veins.

Which bowel and bladder effects are expected?

Constipation that can progress to paralytic ileus, and urinary retention.

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