Pharmacology · Direct vasodilators
Minoxidil !
A powerful oral vasodilator kept for severe, resistant hypertension. It is given with a beta blocker and a diuretic, and it makes body hair grow.
Updated 2026-11-01
Mechanism of action
Minoxidil is a prodrug: its sulfate metabolite opens ATP-sensitive potassium channels in arteriolar smooth muscle. Potassium leaves the cell, the membrane hyperpolarises, calcium entry falls and the arterioles relax; veins are hardly affected. The large fall in resistance triggers reflex tachycardia, higher cardiac output and strong salt and water retention.
- Minoxidil is sulfated to its active form
- Minoxidil sulfate opens ATP-sensitive potassium channels
- Arteriolar muscle hyperpolarises and relaxes
- Reflex tachycardia and fluid retention follow
Pharmacokinetics
- Absorption
- At least 90 percent absorbed from the gut (label)
- Metabolism
- Mostly metabolised, mainly by glucuronidation; the active form is minoxidil sulfate
- Elimination
- Metabolites leave mainly in urine; removed by haemodialysis
- Half-life
- Plasma half-life about 4.2 hours (label); the effect lasts much longer
Indications
- Severe hypertension that is symptomatic or damages organs and is not controlled by a diuretic plus two other antihypertensives Arterial hypertension →
- Other form: topical minoxidil for androgenetic alopecia
Adverse effects
Common
- Hypertrichosis: longer, thicker, darker body hair
- Tachycardia
- Salt and water retention with oedema and weight gain
- Headache and sweating
Contraindications
- Pheochromocytoma
- Hypersensitivity to minoxidil
Key interactions
- Guanethidine
- Profound orthostatic hypotension
- Beta blockers
- Used together on purpose to prevent tachycardia and extra myocardial work
- Diuretics
- Needed to prevent fluid retention and heart failure
What is monitored
- Blood pressure and heart rate
- Body weight and oedema
- Signs of pericardial effusion: breathlessness, chest pain, muffled heart sounds
- Angina
Nursing care
- Weigh the patient regularly; report a rapid weight gain or new swelling.
- Check the pulse; report a resting heart rate that rises clearly above the usual value.
- Report shortness of breath, chest pain or dizziness, which can signal pericardial effusion.
- Explain that hair growth on the face and body is an expected effect.
Pregnancy and breastfeeding
Animal studies showed more fetal resorption in rabbits; it is used in pregnancy only if the benefit clearly justifies the risk.
Test yourself
Think of the answer, then tap the question to see it.
How does minoxidil relax arterioles?
Its sulfate metabolite opens ATP-sensitive potassium channels; the membrane hyperpolarises, calcium entry falls and the muscle relaxes.
Why is minoxidil given with a beta blocker and a loop or thiazide diuretic?
To counter the reflex tachycardia and the marked salt and water retention caused by the fall in resistance.
Which serious cardiac effusion can minoxidil cause?
Pericardial effusion, which can progress to cardiac tamponade.
Which adverse effect led to the topical use of minoxidil?
Hypertrichosis: growth of body hair, used topically to treat androgenetic alopecia.
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 - MINOXIDIL tablet (DailyMed (U.S. National Library of Medicine), 2026); Minoxidil: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2018); 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.