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Magnesium citrate / oxide (constipation + general)

Osmotic-effect magnesium forms, distinct from glycinate's sleep use, useful for occasional constipation and as general magnesium supplementation.

Why

Magnesium citrate and magnesium oxide are widely-used non-stimulant osmotic laxatives at higher doses, and general magnesium-deficiency supplements at lower doses. EFSA-authorised claims cover magnesium's contribution to normal muscle function, normal nervous system function, reduction in tiredness and fatigue, and electrolyte balance. Citrate is better-absorbed than oxide; oxide is cheaper and has stronger osmotic-laxative effect at high doses.

How it works

Magnesium ions are osmotically active in the gut lumen, drawing water in and softening stool. Systemically absorbed magnesium is a cofactor in over 300 enzymatic reactions, energy production (ATP), nerve conduction, muscle contraction, and calcium homeostasis.

Expected onset · Laxative effect within 6–24 hours; general supplementation effects emerge over weeks

How to take

Dosage

Constipation: 200–400 mg elemental magnesium at bedtime or split. General supplementation: 200–400 mg elemental magnesium/day. Note total includes magnesium from food.

Timing

Constipation use: bedtime. General use: with meals.

On the label

'Magnesium citrate' (better absorbed) or 'magnesium oxide' (stronger laxative). Stated elemental magnesium per dose (not salt weight). For sleep/relaxation use, see magnesium-glycinate.

Ideal for

Adults with occasional constipation; adults with low magnesium intake; people with muscle cramps, tension, or low-grade fatigue (general supplementation use).

Safety

Avoid or use very cautiously in kidney disease, impaired magnesium excretion can cause hypermagnesaemia (weakness, hypotension, arrhythmia). Diarrhoea is dose-limiting and is the main reason to titrate. Reduces absorption of tetracyclines, quinolones, bisphosphonates and levothyroxine. Separate by 2–4 hours. Pregnancy: dietary doses safe; supplement doses fit standard prenatal practice.

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Evidence

At a glance

EFSA authorised four separate claims for magnesium, muscle, nervous system, tiredness/fatigue, electrolyte balance, the highest regulatory tier in EU food law. Mori 2019 Sci Rep RCT (n=34 chronic constipation): magnesium oxide 1.5 g/day significantly improved stool frequency, consistency and QoL over 28 days. Walker 2003 confirmed superior bioavailability of citrate vs oxide.

Where to get it

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