Magnesium for Constipation: Does Magnesium Make You Poop? Best Type and Dose

Does magnesium make you poop?

It can, depending on the form and the dose. Some magnesium salts are poorly absorbed, so they stay in the gut and pull water into the bowel by osmosis. That softens stools and makes them easier to pass. This is why magnesium hydroxide (milk of magnesia) and magnesium sulphate (Epsom salts) are sold as laxatives, and why too much magnesium from supplements causes diarrhoea.

The BNF, the reference book UK doctors and pharmacists use, lists magnesium hydroxide and magnesium sulphate alongside lactulose and macrogol as osmotic laxatives. Osmotic laxatives work by increasing the amount of water in the large bowel.

Two things decide whether a magnesium product makes you go:

• The form. Oxide, hydroxide and sulphate have the strongest effect. Citrate is in the middle. Glycinate, malate and threonate are rarely noticed by the bowel at normal amounts.
• The amount. A laxative dose is far bigger than a typical daily supplement. The NHS says taking more than 400mg of magnesium for a short time can cause diarrhoea, while 400mg or less a day from supplements is unlikely to cause harm.

So a low-dose supplement may cause no change at all, or slightly softer stools in the first few days. A pharmacy laxative is designed to make you poo, often the same day.

How fast each form works

Timings below are for laxative doses taken as directed on the pack. Everyday supplement doses are much smaller and may have little or no effect on the bowel.

For comparison, the NHS says the common osmotic laxatives lactulose and macrogol take 2 to 3 days to work, and stimulant laxatives such as senna take 6 to 12 hours. Fast-acting magnesium salts are best kept for occasional use: US drug information for both magnesium citrate and magnesium hydroxide says not to use them for more than a week without speaking to a doctor.

For every form side by side, see types of magnesium and their uses.

What the research shows

Magnesium oxide is the only form with good trials in chronic constipation.

• A 2021 Japanese trial. 90 adults with chronic constipation took magnesium oxide (1.5g a day), senna or placebo for four weeks. About 68% improved with magnesium oxide and 69% with senna, compared with 12% on placebo. Nobody had a severe side effect.
• A 2023 King’s College London review. It pooled the trials of food, vitamin and mineral supplements for constipation. The only magnesium in it was oxide (two trials): 68% responded, against 19% on placebo, with about 3.7 more bowel movements a week and softer stools.
• The 2025 British Dietetic Association guidelines. These were the first UK dietary guidelines for chronic constipation in adults. They made a strong recommendation for magnesium oxide, at 0.5g to 1.5g a day for at least four weeks, starting at 0.5g a day and increasing weekly while watching how well it is tolerated. That is a clinical dose of the compound, best agreed with a GP, pharmacist or dietitian.
• Magnesium-rich mineral water. In a 2017 trial in adults with constipation, 500ml a day of a mineral water rich in magnesium sulphate improved bowel movements and stool consistency over six weeks, compared with ordinary water. A 2026 German trial using a litre a day saw more bowel movements at two weeks, but no clear difference from ordinary water by week three. The BDA guidelines suggest high-mineral water can help some people.

There are no good trials of magnesium citrate or glycinate supplements for chronic constipation. Citrate’s laxative effect is well known from pharmacy products, but the daily-supplement evidence is for oxide.

Which magnesium is best for constipation?

• If you want a laxative: speak to a pharmacist first. Magnesium hydroxide is sold in UK pharmacies for constipation, and magnesium oxide has the best evidence for long-standing constipation.
• If you want everyday magnesium that may soften stools a little: citrate is a good middle ground. More in our magnesium citrate guide.
• If you want magnesium without a laxative effect: glycinate is the gentlest choice. See magnesium glycinate.
• Epsom salts by mouth: only if a pharmacist or doctor advises. They act fast and strongly.

If constipation comes with bloating, our magnesium for bloating guide explains which forms make sense. If you have IBS, read our IBS guide first, as magnesium can make IBS with diarrhoea worse.

Magnesium glycinate vs citrate for your bowels

Is magnesium glycinate a laxative? No. In magnesium glycinate (bisglycinate), magnesium is bound to the amino acid glycine. A small 1994 study suggested some of it is absorbed intact through a different route from other magnesium salts, and in that study it was better tolerated than magnesium oxide. Less magnesium is left in the bowel to pull in water, so most people notice little or no change in their stools.

Does magnesium citrate make you poop? It can. Citrate is well absorbed, but at larger amounts some stays in the gut and draws in water. That is why citrate is used in some pharmacy laxatives and bowel preparations, and why a citrate supplement can make stools a little looser, especially when you first start.

Taking both together, as many blends do, gives a middle path: the gentleness of glycinate with some citrate.

Magnesium citrate and magnesium oxide benefits

Both are sources of magnesium, a mineral your body needs every day. The NHS says adults aged 19 to 64 need 300mg a day (men) or 270mg a day (women), and you should be able to get all you need from a varied and balanced diet. As a nutrient, magnesium contributes to:

• a reduction of tiredness and fatigue
• normal muscle function
• normal functioning of the nervous system
• normal psychological function
• electrolyte balance
• the maintenance of normal bones and teeth

Magnesium citrate benefits in short: a well-absorbed, easy-to-take form for everyday top-ups. At larger doses it is used as a laxative, which is a medicine use rather than a supplement one. Full guide: magnesium citrate uses, dose and side effects.

Magnesium oxide benefits in short: it is cheap and widely used as a laxative and an antacid. It is one of the less well-absorbed forms, which is exactly why it works on the bowel and why it is less suited to everyday top-ups. Full guide: magnesium oxide uses and absorption.

Our Magnesium Glycinate Sleep Complex and your gut

Our Magnesium Glycinate Sleep Complex is an evening drink, not a laxative. It combines magnesium bisglycinate and magnesium citrate, giving 290mg of magnesium per serving, well inside the NHS 400mg guide for supplements, plus glycine, L-theanine, chamomile, passionflower, hops and oat straw.

• What to expect: most people notice no change in their bowels. The citrate part may make stools a little softer in some people, while the glycinate part is gentle.
• Sensitive gut? Start with a half serving for the first week, then build up.
• Magnesium contributes to normal muscle function and to a reduction of tiredness and fatigue.
• Who it’s for: adults (18+) only. We don’t recommend our products during pregnancy or breastfeeding. If you take any medication, check with your GP or pharmacist first, and don’t take magnesium supplements if you have kidney disease unless your doctor advises it.

The FSA’s 10mg a day figure for CBD is precautionary advice rather than a legal limit, set while longer-term safety research continues. At Evopure we think it is a very cautious figure, and many adults use more. If you go above it, increase slowly, and check with your GP or pharmacist first if you take any medication.

How much and how fast?

• Follow the pack or your pharmacist’s advice for laxative products; they’re for short-term use.
• As a supplement, the NHS says 400mg or less a day of magnesium from supplements is unlikely to cause harm. Higher amounts are more likely to cause diarrhoea.
• Speed: magnesium citrate and hydroxide laxatives usually work within 30 minutes to 6 hours, and Epsom salts within 2 to 4 hours. Magnesium oxide taken daily works more gradually.
• If it isn’t working: the NHS says to speak to a doctor or pharmacist if laxatives haven’t helped after 3 days.
• Drink plenty of water alongside, as magnesium works by drawing water into the bowel. Not sure how much? See how much water should I drink a day.
• Leave a gap from other medicines: US drug information advises taking other medicines at least 2 hours before or after a magnesium citrate laxative.

Can you take magnesium every day for constipation?

It depends what you mean by magnesium.

• Pharmacy laxatives: without a prescription, the NHS says to stop when your constipation improves and not to take laxatives for longer than 7 days.
• Daily magnesium oxide: trials and the BDA guidelines used it for at least four weeks, but at clinical doses. Do this with your GP, pharmacist or dietitian, not on your own.
• An everyday supplement within 400mg: fine for most adults, but don’t rely on it to fix ongoing constipation.

The main risk of long-term, high-dose use is too much magnesium in the blood. In a Japanese hospital study of 320 patients prescribed magnesium oxide, 23% developed raised blood magnesium. The risk was higher with reduced kidney function, doses of 1,650mg a day or more, and use for 36 days or longer. That is why older adults and anyone with kidney problems should only use magnesium laxatives under medical advice.

Side effects and who should avoid it

• Kidney disease: don’t use magnesium laxatives or supplements without your doctor’s advice, as magnesium can build up to dangerous levels. The BNF advises caution with magnesium hydroxide in kidney impairment and avoiding it in severe kidney failure.
• Older adults and long-term use: check with a GP; high magnesium levels have been reported with regular magnesium oxide use.
• Medicines: magnesium can reduce absorption of some antibiotics, thyroid and osteoporosis medicines. Leave a gap and ask your pharmacist.
• Side effects: diarrhoea, cramping and wind.
• Pregnancy and breastfeeding: the NHS says to check with a pharmacist or doctor before taking laxatives. Only use a laxative recommended by your midwife, GP or pharmacist.
• Children: only use a laxative if a GP recommends it. See magnesium and constipation in children.

For side effects of magnesium in general, including how to avoid them, see magnesium side effects.

What to try first (NHS)

• More fibre: fruit, vegetables, wholegrains, oats and pulses, increased gradually
• Fruits that contain sorbitol, such as apples, apricots, grapes, raisins, raspberries and strawberries
• Wheat bran, oats or linseed added to your diet
• Plenty of fluids, especially water, and less alcohol
• Regular exercise, such as a daily walk
• A regular time and place to go, without rushing or delaying
• Raising your feet on a low stool while on the toilet

The NHS says you may notice a difference within a few days, though it can take a few weeks. The BDA guidelines also back kiwifruit, prunes, rye bread and psyllium. Our guides to foods that help constipation, high fibre foods and flaxseed (linseed) show how to build up slowly. For the bigger picture, see how to improve your gut health and our guide to probiotics.

iIf these don’t help, a pharmacist can suggest a suitable laxative. Constipation is also common with weight-loss injections: see magnesium and Mounjaro.

When to see a GP

iThe NHS says to see a GP if you:

• are constipated and it’s not getting better with treatment
• are regularly constipated or regularly bloated
• have blood in your poo
• have lost weight without trying
• are constipated and feel tired all the time
• are taking medicine that’s causing constipation, such as opioid painkillers
• notice a sudden change in your bowel habits, or have tummy pain

iSpeak to your GP before you stop taking any prescribed medicine.

Related guides

• If you’d rather drink your magnesium, our guide to magnesium powder compares glycinate and citrate powders for gut comfort.
• Not sure whether to take it morning or night? See the best time to take magnesium, including citrate and oxide.
• If you take CBD as well, see whether CBD can cause constipation.
• Taking it at night? See magnesium for sleep for why a big dose of citrate at bedtime can wake you up, and which form is gentler.
• Buying for another reason too? Our magnesium supplements UK guide shows which form suits which need.
• Some multi-form products rely on oxide or citrate; see side effects of magnesium complexes for how that affects your stomach.
• Vitabiotics Ultra Magnesium and magnesium hydroxide.
• For other goals, magnesium takes much longer: see how long does magnesium take to work?
• Citrate suits constipation best; see how it compares in magnesium glycinate vs citrate vs threonate.
• Wondering about a fizzy citrate drink? See is Natural Vitality Calm a laxative?
• Many magnesium-rich foods, such as beans, seeds and wholegrains, are high in fibre too.
• Unabsorbed magnesium leaves with your next bowel movements; more in how long magnesium stays in your system.