Pharmacology · Centrally acting antihypertensives
Methyldopa !
An older oral blood pressure medicine that acts in the brain. It is still a classic choice for high blood pressure in pregnancy.
Updated 2026-11-01
Also called: Alpha-methyldopa
The figure shows noradrenaline bound to the human alpha-2A adrenergic receptor; alpha-methylnorepinephrine, the active metabolite of methyldopa, acts at the same site.
Mechanism of action
Methyldopa is an analogue of L-dopa. In adrenergic neurons it is converted to alpha-methyldopamine and then alpha-methylnorepinephrine. The metabolite stimulates alpha-2 receptors in the brainstem, reducing sympathetic outflow, so peripheral resistance falls with little change in cardiac output.
- Methyldopa is converted to alpha-methylnorepinephrine in neurons
- The metabolite stimulates central alpha-2 receptors
- Sympathetic outflow and peripheral resistance fall
Pharmacokinetics
- Absorption
- Oral; absorption is incomplete and reduced by iron salts
- Metabolism
- Converted in neurons to its active metabolite; also conjugated as a sulfate
- Elimination
- Mostly by the kidneys; removed by dialysis
- Half-life
- Plasma half-life about 105 minutes, but the effect lasts much longer (label)
- Onset and duration
- Maximum fall in pressure several hours after a dose
Indications
- High blood pressure Arterial hypertension →
- High blood pressure in pregnancy, including preeclampsia Preeclampsia →
Adverse effects
Common
- Sedation, mainly at the start or after a dose increase
- Headache and weakness
- Nasal stuffiness
- Orthostatic hypotension and oedema
- Positive direct Coombs test
Contraindications
- Active liver disease (acute hepatitis, active cirrhosis)
- Liver disorders previously caused by methyldopa
- Treatment with MAO inhibitors
- Hypersensitivity, including previous methyldopa-related haemolytic anaemia
Key interactions
- Ferrous sulfate or ferrous gluconate
- Lower methyldopa bioavailability and poorer blood pressure control
- Lithium
- Risk of lithium toxicity
- MAO inhibitors
- Contraindicated combination
- Other antihypertensives and anaesthetics
- Additive fall in blood pressure
What is monitored
- Blood pressure
- Blood count and direct Coombs test before and during treatment
- Liver function, especially in the first months
- Temperature in the first weeks
Nursing care
- Before: baseline blood count, Coombs test and liver tests.
- Warn about drowsiness at the start, so tasks that need alertness are planned around it.
- Report fever, jaundice, dark urine, tiredness or pallor (possible hepatitis or haemolysis).
- Methyldopa can make urine catecholamine tests read falsely high: tell the laboratory.
- Before a transfusion, the blood bank is told the patient takes methyldopa (Coombs test).
Pregnancy and breastfeeding
Used in all trimesters; published experience suggests the possibility of fetal harm is remote (label), which is why it remains a classic antihypertensive in pregnancy.
Test yourself
Think of the answer, then tap the question to see it.
How does methyldopa lower blood pressure?
It is converted to alpha-methylnorepinephrine, which stimulates alpha-2 receptors in the brainstem and reduces sympathetic outflow and peripheral resistance.
Which laboratory finding appears in some patients on long-term methyldopa?
A positive direct Coombs test; a few develop autoimmune haemolytic anaemia, so blood counts are checked.
In which group of patients is methyldopa still a classic choice?
Pregnant women with high blood pressure, because long experience suggests the fetal risk is remote.
Which common supplement reduces the absorption of methyldopa?
Iron salts (ferrous sulfate or gluconate), which lower its bioavailability and blood pressure control.
Related drugs
Related conditions
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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 - METHYLDOPA tablet (DailyMed (U.S. National Library of Medicine), 2025); Methyldopa: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2017); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); Farmacología básica y clínica (Katzung), cap. 11 (McGraw Hill, 2025).
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Representative model, for educational purposes only.