Sleep, stress and recovery

Magnesium citrate

Also called: mag citrate

Magnesium citrate is magnesium bound to citric acid. It is moderately well-absorbed, but its main use is its osmotic effect in the colon: it pulls water in and softens stool. Standard dose for constipation is 200 to 400 mg of elemental magnesium at bedtime. Often the cheapest and most effective first-line option for slow-transit constipation.

How it works

Magnesium citrate is moderately well-absorbed in the small intestine, Schuchardt & Hahn 2017 cite a general intestinal Mg absorption range of 30-50%, with citrate showing relatively higher bioavailability than oxide in head-to-head comparisons (Walker 2003). The unabsorbed fraction reaches the colon, where the magnesium pulls water osmotically into the lumen. This softens the stool and stimulates colonic motility. Onset for the laxative effect at supplement doses ranges from 30 minutes to 6 hours (MedlinePlus); bedtime dosing typically produces a morning bowel movement.

When to use it

  • Slow-transit constipation that has not responded to fibre + water + movement.
  • GLP-1-induced constipation (Ozempic, Wegovy, Mounjaro).
  • Travel constipation.
  • Daily use for chronic constipation under GP guidance.
  • NOT for diarrhoea or loose stools (will make worse).
  • Not the best form for sleep or anxiety, use glycinate for those.

Magnesium citrate vs glycinate

  • Citrate: pulls water into colon, softens stool, mild laxative.
  • Glycinate: gentle on gut, no laxative effect, better for sleep and anxiety.
  • Both well-absorbed.
  • Citrate is cheaper.
  • If you want both effects (e.g. better sleep AND regular bowels), take glycinate at bedtime and a smaller dose of citrate as needed.

Dosing

  1. Start with 200 mg elemental magnesium at bedtime.
  2. Build up to 400 mg if needed; that is the typical effective dose for chronic constipation.
  3. Dissolve powder in water 30 minutes before bed.
  4. Effect typically appears within 30 minutes to 6 hours; bedtime dosing usually means a morning bowel movement.
  5. If diarrhoea results, dose was too high. Dial back.

What to watch

  • Kidney disease: cannot clear excess magnesium safely. Talk to a doctor before use.
  • On other meds: spaces out from antibiotics, bisphosphonates, thyroid meds by 2 hours.
  • Above 600 mg/day: usually causes diarrhoea, electrolyte loss possible.
  • If you need it daily for more than 4 to 6 weeks, see a GP, chronic constipation deserves investigation, not just laxatives.

Common questions

Will I get dependent on it?
Magnesium citrate does not cause laxative dependence the way stimulant laxatives (senna, bisacodyl) can. The osmotic effect is mechanical, not nerve-based. Long-term daily use is reasonable if needed.
How fast does it work?
30 minutes to 6 hours, per MedlinePlus and the BNF, depending on dose. A bedtime supplement dose typically produces a morning bowel movement. High-dose 'liquid' magnesium citrate (used for bowel prep) is at the faster end and far more aggressive.
Can I take it with food?
Yes, food slightly reduces absorption but improves tolerance. For sleep effect, take with dinner; for constipation effect, take 1 hour after dinner with water.
Does it interact with my GLP-1?
No direct interaction. In fact, magnesium citrate is one of the recommended first-line additions for GLP-1 constipation. Take it at bedtime; doesn't affect the weekly GLP-1 dose.

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