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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Centrally acting antihypertensives

Blood pressure medicines that act in the brainstem to turn down the sympathetic nervous system. Methyldopa is a classic choice in pregnancy.

Updated 2026-11-01

## What they are

Alpha-2 adrenergic agonists that lower sympathetic outflow from the brainstem: clonidine and methyldopa (a prodrug). They are no longer first-line for most people with hypertension, but methyldopa is still used for high blood pressure in pregnancy and clonidine has other uses (attention deficit hyperactivity disorder, withdrawal syndromes).

## Mechanism of action

Stimulating alpha-2 receptors in the vasomotor centres of the brainstem reduces sympathetic outflow to the heart, vessels and kidneys, so peripheral resistance, heart rate and renin fall. Methyldopa works through its metabolite alpha-methylnorepinephrine, which acts on the same central receptors.

Target: Alpha-2A adrenergic receptor in the brainstem

## Key points

- Stopping clonidine suddenly can cause rebound hypertension with agitation, headache and tremor; it is withdrawn gradually.
- Typical adverse effects: sedation, dry mouth, dizziness and bradycardia.
- Methyldopa can cause a positive Coombs test, haemolytic anaemia and hepatitis.
- Methyldopa remains a classic antihypertensive for pregnancy.

## Drugs in this class

- [**Methyldopa** An older oral blood pressure medicine that acts in the brain. It is still a classic choice for high blood pressure in… Alpha-2A adrenergic receptor (through alpha-methylnorepinephrine)](https://durgical.com/en/pharmacology/methyldopa/)
- [**Clonidine** A blood pressure medicine that calms the sympathetic nervous system from the brainstem. Stopping it suddenly can make… Alpha-2A adrenergic receptor](https://durgical.com/en/pharmacology/clonidine/)

## Others in the class

- Guanfacine
- Moxonidine
- Rilmenidine

## Test yourself

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

## Why does sudden withdrawal of clonidine raise blood pressure?

Sympathetic outflow, suppressed by the drug, rebounds: catecholamine release rises and blood pressure can overshoot, with agitation, headache and tremor.

## What is the active metabolite of methyldopa?

Alpha-methylnorepinephrine, which stimulates central alpha-2 receptors and lowers sympathetic outflow.

## Which haematological finding is typical of methyldopa?

A positive direct Coombs test; a few patients develop autoimmune haemolytic anaemia.

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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: [DailyMed - CLONIDINE HYDROCHLORIDE tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=cf493e6a-1603-4c7d-a442-69a119bec843) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - METHYLDOPA tablet](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9e22e1d8-04ec-4b67-92ea-b09c706f2703) (DailyMed (U.S. National Library of Medicine), 2025); Farmacología básica y clínica (Katzung), cap. 11 (McGraw Hill, 2025).

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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/centrally-acting-antihypertensives/