Magnesium citrate: uses and side effects

What is magnesium citrate?

Magnesium citrate is magnesium joined to citric acid, the acid found in lemons. It's one of the most common forms in UK supplements, because the body absorbs it well and it costs little.

Magnesium itself is a mineral your body needs every day. The NHS says adults need 300 mg a day for men and 270 mg a day for women [1].

What is magnesium citrate good for?

Its main use is topping up the magnesium you get from food. Magnesium contributes to a reduction of tiredness and fatigue, to normal muscle function, to normal functioning of the nervous system and to normal psychological function. These are authorised health claims in the UK [2].

• Everyday top-up. For days when your diet is short of foods such as spinach, nuts and wholemeal bread [1].
• Good absorption. In trials, including one at the University of Reading, more magnesium reached the blood and urine from citrate than from magnesium oxide [3, 4].
• A form with long-term data. In a 24-week trial, citrate raised blood and urine magnesium compared with a placebo [5].

How well is magnesium citrate absorbed?

Well, and better than magnesium oxide in several trials. Most citrate research measures absorption, not health outcomes. Each finding has a label: Strong (several good trials agree), Moderate, Early (one or two small trials) or Mixed.

In the 24-week trial, citrate didn't change artery stiffness or blood pressure compared with a placebo [5]. So good absorption tells you the magnesium gets in, not that it does more once it's there.

Magnesium citrate vs glycinate: which is better?

Neither is clearly better: both are organic forms that absorb well. Glycinate is often chosen by people with a sensitive stomach and has a recent sleep trial, but few trials compare the two directly.

Read more in our complete guide to magnesium glycinate and our guide to magnesium for sleep.

Can magnesium citrate cause diarrhoea?

Yes, especially at higher doses. Taking more than 400 mg of magnesium a day can cause diarrhoea [1], and stomach cramps or feeling sick are possible too.

Magnesium that isn't absorbed holds water in the bowel, which loosens stools. In a Cochrane review, digestive side effects such as diarrhoea affected 11% to 37% of people taking magnesium, against 10% to 14% on a placebo [8]. Taking it with food or splitting the dose often helps.

This effect is why some magnesium salts are used as laxatives, at much higher doses than a daily top-up. In two trials in adults with long-term constipation, 68% responded to magnesium oxide, against 19% in the comparison groups [9]. Liquid magnesium citrate used before a hospital bowel test is a medicine, not a supplement, so follow the hospital's instructions.

Can magnesium cause constipation?

It's unlikely. Magnesium tends to loosen stools rather than firm them, and trials report mostly diarrhoea-type side effects, not constipation [8].

If you feel constipated while taking a supplement, check its other ingredients and ask a pharmacist.

Is it safe to take magnesium citrate daily?

Yes, for most adults, at 400 mg of magnesium a day or less from supplements [1]. Count every product you take, including multivitamins.

• Kidney problems. Your kidneys clear extra magnesium, so ask your GP first.
• Antibiotics. Magnesium can stop tetracyclines and quinolones being absorbed properly. Take magnesium at least 4 hours before or 2 hours after them [10].
• Bone medicines or levothyroxine. These may need to be taken a few hours apart from magnesium. Ask your pharmacist.
• Pregnancy or other regular medicines. Ask your GP or pharmacist first.

When should you take magnesium citrate?

At any time of day that suits you. No trial has compared timings, and many people take it in the evening.

Tablets, capsules, powders and liquids all work. Check the magnesium figure on the label, not the weight of the citrate, because that's what counts towards the 400 mg guide.

Where Nooroots fits

Nooroots Triple Magnesium contains 500 mg of magnesium citrate, with glycinate and malate, for 301 mg of magnesium in three vegan capsules a day.

It's made for an easy daily magnesium top-up. Triple Magnesium's magnesium helps reduce tiredness and fatigue, and supports normal muscle function and normal psychological function.

Coming soon. Triple Magnesium isn't on sale yet.

Frequently asked questions

Does magnesium citrate make you poo?

It can, especially at higher doses, because magnesium that isn't absorbed draws water into the bowel. Above 400 mg a day from supplements, diarrhoea becomes more likely [1].

Is magnesium citrate good for you?

For most adults, yes, as a way to top up magnesium. It's well absorbed, and magnesium helps reduce tiredness and fatigue [2, 3].

Does magnesium citrate help you sleep?

Little research has tested citrate for sleep. The most recent sleep trial used magnesium bisglycinate, and found a small benefit after 4 weeks [7].

Can magnesium glycinate cause diarrhoea?

It can, like any magnesium, mainly at high doses. Keeping to 400 mg of magnesium a day or less from supplements makes it less likely [1].

Can you take magnesium citrate and glycinate together?

Yes. They're two forms of the same mineral, so add up the magnesium from both and keep the total from supplements to 400 mg or less [1].

How much magnesium do you need a day?

The NHS says 300 mg a day for men and 270 mg for women aged 19 to 64, from food and supplements together [1].

References

Every study here is listed so you can read it yourself. This guide is for general information and doesn't replace advice from your GP or pharmacist. We review it when new research is published.

1. NHS. Vitamins and minerals: others (magnesium section). Accessed 17 October 2026. nhs.uk/conditions/vitamins-and-minerals/others
2. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. Updated 19 May 2026. gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register
3. Walker AF et al. (2003). Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research 16(3): 183–191. PMID 14596323
4. Werner T et al. (2019). Assessment of bioavailability of Mg from Mg citrate and Mg oxide by measuring urinary excretion in Mg-saturated subjects. Magnesium Research 32(3): 63–71. PMID 32162607
5. Schutten JC et al. (2022). Effects of magnesium citrate, magnesium oxide, and magnesium sulfate supplementation on arterial stiffness: a randomized, double-blind, placebo-controlled intervention trial. Journal of the American Heart Association 11(6): e021783. doi:10.1161/JAHA.121.021783
6. Merschmann R et al. (2025). Bioavailability of magnesium and potassium salts used as potential substitutes for sodium chloride in human nutrition: a review. Molecular Nutrition & Food Research 69(22): e70227. doi:10.1002/mnfr.70227
7. Schuster J et al. (2025). Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomized, placebo-controlled trial. Nature and Science of Sleep 17: 2027–2040. doi:10.2147/NSS.S524348
8. Garrison SR et al. (2020). Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews 9: CD009402. doi:10.1002/14651858.CD009402.pub3
9. van der Schoot A et al. (2023). The effect of food, vitamin, or mineral supplements on chronic constipation in adults: a systematic review and meta-analysis of randomized controlled trials. Neurogastroenterology and Motility 35(11): e14613. doi:10.1111/nmo.14613
10. Ogawa R, Echizen H (2011). Clinically significant drug interactions with antacids: an update. Drugs 71(14): 1839–1864. doi:10.2165/11593990-000000000-00000