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, intestinal magnesium absorption varies roughly from 35% to 70% depending on dose and status, with citrate showing 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; glycinate is the form usually preferred for those, though evidence is limited.

Magnesium citrate vs glycinate

  • Citrate: pulls water into colon, softens stool, mild laxative.
  • Glycinate: gentle on gut, no laxative effect, often preferred for sleep and anxiety (though the trial evidence specific to glycinate is limited).
  • 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; higher daily magnesium doses are what trials have shown effective 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: space out from antibiotics and bisphosphonates by 2 hours, and from thyroid meds (levothyroxine) by 4 hours.
  • Higher supplement doses commonly cause diarrhoea; the upper level for supplemental magnesium is 350 mg/day, with loose stools as the limiting effect, and 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. Osmotic laxatives are a standard option for GLP-1 constipation; guidelines usually put polyethylene glycol (PEG/Miralax) first, with magnesium as an alternative. Take it at bedtime; doesn't affect the weekly GLP-1 dose.

Sources

The Book of Suna is general information, not medical advice. It is not a substitute for talking to a qualified healthcare professional about your own situation.