Magnesium Citrate: Uses, Benefits, Dosage & Safety
Last updated: August 2026 · Reviewed by the FactoWiki Editorial Team for clarity and source accuracy
Quick summary
Magnesium citrate is well absorbed and has a notable laxative effect, which makes it a good choice if constipation is part of the picture and a poor one if it is not. It is among the better-absorbed affordable forms.
What is Magnesium Citrate?
Magnesium bound to citric acid. Absorption is considerably better than magnesium oxide — studies put it among the higher-bioavailability forms — and it is inexpensive. Elemental magnesium content is around 16% by weight, so a 500 mg capsule of magnesium citrate supplies roughly 80 mg of actual magnesium.
What Magnesium Citrate is commonly used for
Correcting magnesium shortfall, constipation and bowel regularity, muscle cramps, and as a bowel preparation at high doses.
How Magnesium Citrate works
Magnesium is a cofactor in over 300 enzyme reactions including ATP metabolism, and regulates NMDA receptors and GABA activity. The laxative effect is osmotic: unabsorbed magnesium draws water into the intestine, which is why the better-absorbed forms are gentler and the poorly absorbed ones are not.
What the evidence says
Each claim below is tied to the specific study behind it, rather than to a general reading list.
- Magnesium citrate showed higher bioavailability than magnesium oxide in comparative absorption studies. Walker et al., Magnesium Research, 2003 — randomised crossover bioavailability study. (PubMed)
- Magnesium is a cofactor in more than 300 enzymatic reactions. NIH Office of Dietary Supplements — Magnesium Fact Sheet for Health Professionals. (PubMed)
- Osmotic magnesium salts are effective for constipation. Mori et al., Journal of Neurogastroenterology and Motility, 2019 — randomised controlled trial. (PubMed)
Typical dosage used in studies
200–400 mg of elemental magnesium daily for general supplementation — check the elemental figure, not the compound weight. Higher doses are used deliberately for constipation. Splitting the dose improves tolerance.
Side effects and safety
Well tolerated at normal doses. Loose stools are the dose-limiting effect and the most common complaint. The tolerable upper intake for supplemental magnesium is 350 mg elemental daily for adults, above which diarrhoea becomes likely.
Medication interactions and who should avoid Magnesium Citrate
Medication & safety check
Magnesium reduces absorption of tetracycline and quinolone antibiotics, bisphosphonates and levothyroxine — separate doses by at least two hours. People with reduced kidney function can accumulate magnesium and should not supplement without medical advice.
General information, not personal medical advice. If you take any medication, confirm it is safe to combine with Magnesium Citrate with your doctor or pharmacist first.
Sources & further reading
The claim-level citations above are drawn from these sources:
- Walker et al., Magnesium Research, 2003 — randomised crossover bioavailability study — find on PubMed
- NIH Office of Dietary Supplements — Magnesium Fact Sheet for Health Professionals — find on PubMed
- Mori et al., Journal of Neurogastroenterology and Motility, 2019 — randomised controlled trial — find on PubMed
- NIH Office of Dietary Supplements
- NIH National Center for Complementary and Integrative Health
Frequently asked questions
Citrate or glycinate?
Glycinate if you want magnesium without a laxative effect — for sleep, cramps or general repletion. Citrate if constipation is also something you want to address. Both are well absorbed.
How much elemental magnesium am I getting?
Roughly 16% of the compound weight. A 500 mg magnesium citrate capsule supplies about 80 mg elemental. Labels vary in which figure they show.
Will it cause diarrhoea?
At higher doses, likely. Start low, split the dose, and reduce if stools loosen.
Part of a wider guide
Magnesium Citrate is one form of Magnesium. This page covers what is specific to this form — absorption, tolerability, dosing and who it suits. For the underlying nutrient itself, its overall evidence base and general safety, read the Magnesium guide.
Where you'll find Magnesium Citrate
Magnesium Citrate appears in Minerals & Digestive Support formulas. Browse the supplement guides to see the products we review, each with a full breakdown of formula, pricing and safety.
Related ingredients to explore
Ingredients often studied or formulated alongside Magnesium Citrate.
General information, not medical advice.