Osmotic laxative / antacid

Magnesium hydroxide

Brand names: Milk of Magnesia

Magnesium hydroxide is a magnesium salt used as an antacid for dyspepsia and as an osmotic laxative for constipation.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It neutralises gastric acid to relieve acid-related symptoms and, in the bowel, acts osmotically to retain water and stimulate evacuation.

Prescribing in practice

Magnesium can accumulate and cause hypermagnesaemia in renal impairment, so use with caution and avoid in significant renal failure.
Its laxative effect means it is frequently combined with aluminium-containing antacids to balance bowel effects.
Antacid use can reduce the absorption of other medicines, so separate administration from interacting drugs.

Monitoring

Routine monitoring is not required for occasional use, but assess renal function in patients with impairment or with regular magnesium intake.

Counselling the patient

It can loosen the bowels; leave a gap between this and your other medicines.
Tell your clinician if you have kidney problems or if symptoms persist.

Evidence & guidelines

Magnesium hydroxide is an established antacid and osmotic laxative, with use in constipation and dyspepsia supported by NICE guidance.

Reference: Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways