[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › Ganglionic blockers

# 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

## Key points

- The effect of ganglionic blockade on an organ is the opposite of its predominant autonomic tone.
- Arterioles and veins (sympathetic tone): vasodilation, venous pooling and marked orthostatic hypotension.
- Heart, iris, ciliary muscle, gut and bladder (parasympathetic tone): tachycardia, mydriasis, cycloplegia, constipation or ileus, and urinary retention.
- Dry mouth and reduced sweating are also typical.
- Mecamylamine is a secondary amine that enters the brain; quaternary blockers such as hexamethonium do not.

## Drugs in this class

- [**Mecamylamine** An oral ganglionic blocker for severe hypertension. Blocking both autonomic divisions causes orthostatic hypotension… Neuronal nicotinic acetylcholine receptor of autonomic ganglia (channel blocker)](https://durgical.com/en/pharmacology/mecamylamine/)

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/classes/ganglionic-blockers/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

[← All of pharmacology](https://durgical.com/en/pharmacology/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [DailyMed - MECAMYLAMINE HYDROCHLORIDE tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1b79ef78-f4da-49a6-9f36-89b0da19d39b) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=C02BB01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/pharmacology/classes/ganglionic-blockers/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/ganglionic-blockers/