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# Adrenergic neuron blockers

Old antihypertensives that empty or block the noradrenaline stores of sympathetic nerves. Today they are mostly of historical and exam interest.

Updated Nov 1, 2026

## What they are

Drugs that act inside the sympathetic nerve ending rather than on receptors: reserpine depletes the stores of noradrenaline; guanethidine-type drugs block its release. They gave the first effective treatment of hypertension.

## Mechanism of action

Reserpine binds the vesicular monoamine transporter (VMAT2) almost irreversibly, so vesicles can no longer store noradrenaline, dopamine and serotonin; the amines leak out and are broken down, and little transmitter is released. Guanethidine is taken up into the nerve ending by the noradrenaline transporter and prevents release. The result is a 'chemical sympathectomy'.

Target: Sympathetic nerve ending (VMAT2 for reserpine)

## Key points

- Reserpine also empties brain amine stores: depression, which can be severe, is its key adverse effect.
- Nasal stuffiness, slow heart rate and more stomach acid (peptic ulcer) follow from the loss of sympathetic tone.
- Indirect-acting sympathomimetics (which work by releasing noradrenaline) lose their effect after reserpine.
- Recovery after reserpine needs new vesicles, so the effect lasts days to weeks after stopping.
- Largely replaced by modern antihypertensives.

## Drugs in this class

- [**Metirosine (metyrosine)** A capsule that blocks the first step of catecholamine synthesis. Used to prepare or control patients with… Tyrosine hydroxylase](https://durgical.com/en/pharmacology/metirosine/)
- [**Reserpine** A rauwolfia alkaloid that empties the noradrenaline stores of nerves. The first effective antihypertensive, now rarely… Vesicular monoamine transporter 2 (VMAT2)](https://durgical.com/en/pharmacology/reserpine/)

## Others in the class

- guanethidine
- guanadrel

## Test yourself

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

## Which transporter does reserpine block?

VMAT2, the vesicular monoamine transporter, so vesicles cannot store noradrenaline, dopamine or serotonin.

## Why does ephedrine work poorly in a patient on reserpine?

Ephedrine acts largely by releasing stored noradrenaline, and reserpine has emptied those stores.

## What is the most dangerous adverse effect of reserpine?

Depression, sometimes severe, because brain amines are depleted too.

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

Sources: [Reserpine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a601107.html) (MedlinePlus (U.S. National Library of Medicine), 2024).

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Representative model, for educational purposes only.

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