Too much magnesium: symptoms, maximum dose and how to get rid of it
The short answer
Too much magnesium mostly causes diarrhoea; severe forms are rare and mainly affect people whose kidneys work poorly. EFSA sets the safe upper limit for added magnesium, the kind found in supplements, waters and fortified foods, at 250 mg a day, based on the diarrhoea it can cause. Magnesium naturally present in food does not count towards this limit. Above it, or with kidney failure, magnesium can build up in the blood and cause nausea, muscle weakness, low blood pressure, then breathing and heart problems. To get rid of it: stop the supplement, and see a doctor if symptoms are significant.
This article is for information only and does not replace medical advice. If you have kidney disease or take medication, talk to your doctor or pharmacist.
How much magnesium is « too much »?
| Benchmark | Value | Source |
|---|---|---|
| Adequate intake, adult woman | 300 mg a day, all sources | Anses, 2025 |
| Adequate intake, adult man | 380 mg a day, all sources | Anses, 2025 |
| Safe upper limit, added magnesium | 250 mg a day, supplements, waters, fortified foods | EFSA |
| Safe upper limit in the United States | 350 mg a day, supplements only | Institute of Medicine, 1997 |
The EFSA limit was set from the most common effect, osmotic diarrhoea: poorly absorbed magnesium salts draw water into the gut. It applies to readily dissociable magnesium salts, such as chloride, sulphate, aspartate or lactate, and to magnesium oxide. Magnesium from food is not covered: it is impossible to eat « too much » of it on a normal diet when your kidneys work well.
This limit is debated: a 2023 review (Costello et al., Advances in Nutrition) noted that several recent trials, using doses of 128 to 1,200 mg a day, found no more diarrhoea than with a placebo, and argued for it to be reassessed. In the meantime, 250 mg a day from supplements remains the official benchmark in Europe.
What about water? EFSA includes magnesium added to waters in its limit. Two litres of a very magnesium-rich water such as Hépar, 119 mg per litre according to Ciqual, already provide 238 mg. The laxative effect of this water, however, comes mainly from its sulphates: see our guide to magnesium-rich water.
The 250 mg limit by age
The European safe limit does not only apply to adults. EFSA’s summary table, updated in August 2025, breaks it down by age group:
| Age or situation | Safe limit, added magnesium |
|---|---|
| Child aged 1 to 3 | not determined, for lack of data |
| Child aged 4 to 10 | 250 mg a day |
| Teenager aged 11 to 17 | 250 mg a day |
| Adult | 250 mg a day |
| Pregnancy and breastfeeding | 250 mg a day |
A surprising point: the limit is the same from age 4 as for an adult. Relative to body weight, however, 250 mg weighs more than three times as heavily on a 20 kg child as on a 70 kg adult: always check the magnesium dose of a supplement before giving one to a child, and ask a paediatrician for advice. Before age 4, no limit could be set: no magnesium supplement without a paediatrician’s advice. During pregnancy, the limit remains 250 mg a day of added magnesium, which fits with the advice on cramps given further down.
Symptoms of excess, from mildest to most severe
| Situation | Symptoms | Who is affected |
|---|---|---|
| Digestive excess, the most common | diarrhoea, loose stools, abdominal cramps, nausea | anyone taking too much magnesium as a supplement |
| Build-up in the blood, hypermagnesaemia | nausea, vomiting, low blood pressure, drowsiness, muscle weakness | mainly kidney failure, high doses of magnesium-based laxatives or antacids |
| Severe hypermagnesaemia | marked muscle weakness, breathing difficulties, heart rhythm disturbances, impaired consciousness up to coma | rare: kidney failure, medication overdose |
Hypermagnesaemia is rare, but it can be serious. According to the review by Aal-Hamad et al., it mainly affects people whose kidneys work poorly and those who take medicines or supplements containing magnesium, such as certain laxatives and antacids. With kidney failure, a magnesium supplement should only be taken on medical advice.
Forms of magnesium and their effect on bowel movements
| Form | What you need to know |
|---|---|
| Magnesium oxide | very rich in magnesium per gram, but poorly absorbed; it is also a laxative sold in pharmacies: an effect on bowel movements is common |
| Magnesium chloride | readily dissociable salt, covered by the EFSA limit |
| Magnesium sulphate | well-known laxative, it is what gives some waters their effect |
| Citrate, lactate | common forms in supplements, soluble salts |
| Bisglycinate, glycerophosphate | magnesium bound to an amino acid or to glycerophosphate; often presented as better tolerated by the gut |
If a supplement gives you diarrhoea, there are three solutions: lower the dose, split it into two doses, or change the form. To compare the supplements on the market, their form and their actual dose, see our comparison of the best magnesium supplements.
Does magnesium cause constipation?
No: it is the opposite. Magnesium salts draw water into the gut and tend to have a laxative effect, which is why magnesium oxide and sulphate are used as laxatives. If you feel constipated since starting a supplement, the cause is probably elsewhere: fibre, hydration, other ingredients in the supplement.
Morning or evening? Does magnesium keep you awake?
No official recommendation sets the time of intake, and magnesium is not a stimulant: there is no reason for it to keep you awake. In practice:
- if the supplement gives you digestive problems, take it with a meal, at the lowest effective dose;
- if you take it twice a day, spread the doses between morning and evening;
- if you take medication, follow the interval given by your pharmacist (see below).
For sleep in general, see our guide to foods for sleep.
Magnesium and sleep: what the studies show
Far from keeping you awake, magnesium is often taken in the evening to sleep better. The evidence for this effect is thin. A 2021 meta-analysis found only three trials comparing magnesium with a placebo in older people with insomnia, a total of 151 participants:
| Measure | Result with magnesium |
|---|---|
| Time to fall asleep | shortened by about 17 minutes |
| Total sleep time | lengthened by about 16 minutes, difference not significant |
| Quality of evidence | low to very low, trials at moderate to high risk of bias |
The authors conclude that the literature is too weak to support a firm recommendation. In practice, taking your magnesium in the evening is not a problem, but you should not expect a proven sleep-inducing effect from it. And if your sleep is disturbed for a long time, it is medical advice you need, not a higher dose.
Magnesium and cramps: a disappointing effect
Magnesium is very often recommended for cramps, especially during pregnancy. Cochrane reviews, the benchmark in evidence-based medicine, are nevertheless cautious:
| Situation | What the Cochrane review concludes |
|---|---|
| « Idiopathic » night cramps, especially in older people | differences in cramp frequency were small and not significant compared with placebo: magnesium is unlikely to bring a noticeable benefit |
| Leg cramps during pregnancy | conflicting results between trials, with low to very low certainty evidence; 8 small studies, 576 women |
During pregnancy, the effectiveness of a magnesium supplement against cramps is therefore not established: talk to your midwife or doctor before taking one, and do not exceed the limit of 250 mg a day of added magnesium.
Magnesium and medicines: what to space out
| Combination | Why | What to do |
|---|---|---|
| Magnesium and certain antibiotics, tetracyclines and fluoroquinolones | magnesium reduces their absorption | space out the doses; the interval is given in the leaflet |
| Magnesium and bisphosphonates, for osteoporosis | reduced absorption | space out; follow the leaflet |
| Magnesium and thyroid hormones | absorption possibly reduced | take the supplement at a different time; ask the pharmacist |
| Magnesium and magnesium-based laxatives or antacids | the intakes add up | count everything together, especially with kidney disease |
| Magnesium and vitamin B6, vitamin D | common combinations in supplements | no known problem at usual doses |
Long-term magnesium laxatives: what follow-up studies show
Magnesium oxide is widely used as a laxative in Japan, which has allowed excess blood magnesium to be studied closely in patients taking it every day. In these studies, hypermagnesaemia is defined as 2.5 mg/dL or more, about 1 mmol/L:
| Study | Patients | What was found |
|---|---|---|
| University hospital, 2019 | 320 inpatients on magnesium oxide | 23% with high blood magnesium, including 4% with a severe form; risk factors: reduced kidney function, high urea, a dose of at least 1,650 mg a day, treatment for at least 36 days |
| Chronic constipation, 2019 | 193 patients whose magnesium was measured | 16.6% above 2.5 mg/dL and 5.2% above 3 mg/dL; factors: severe kidney failure, a dose of more than 1,000 mg a day, combination with a stimulant laxative; age alone was not a factor |
| General hospital, 2024 | 256 inpatients | risk factors: high urea, reduced kidney function, a dose of at least 1,000 mg a day; the risk increased with the number of factors |
These figures concern laxatives taken at high doses, often in hospital patients. But the message is clear: the danger comes from the combination of a high dose, a long duration and tired kidneys. The authors recommend regularly measuring blood magnesium in people who have several of these factors. If an elderly relative takes a magnesium laxative every day, talk to their doctor.
Epsom salt: a special case
Epsom salt, sometimes used as a laxative, is made mainly of magnesium sulphate. Several serious poisonings have been reported after swallowing it or receiving it as an enema:
- a 56-year-old man who had taken it as a laxative arrived at A&E weak, with a slow pulse and low blood pressure; he had to be intubated and put on dialysis, with blood magnesium above 3.91 mmol/L. He recovered;
- a 40-year-old woman, whose kidneys were working normally, died after an accidental overdose that caused cardiac arrest;
- a 7-year-old boy died after an Epsom salt enema.
These cases remain rare, but they show that healthy kidneys do not protect against a very large dose taken all at once. Do not take Epsom salt by mouth without medical advice, never use it as an enema in a child, and keep it out of reach.
Sources: Walker P et al., J Emerg Med, 2020; Shoaib Khan M et al., Caspian J Intern Med, 2018; Tofil NM et al., South Med J, 2005.
How do you get rid of excess magnesium?
- Stop the supplement or the source of added magnesium: very magnesium-rich water, laxative, antacid.
- Drink normally: in a person whose kidneys work well, the excess is removed in the urine, and the diarrhoea usually stops quickly.
- See a doctor promptly if you have muscle weakness, unusual drowsiness, feel unwell, have difficulty breathing or palpitations, especially if you have kidney disease: medical treatment relies on stopping the magnesium, hydration by drip and, in severe cases, dialysis.
Meeting your needs through food
Before looking for a supplement, remember that the recommended intakes, 300 mg a day for a woman and 380 mg for a man according to Anses, are most often met through food, and that magnesium from food does not count towards the safe limit. The best sources are nuts and seeds, pulses, wholegrain cereals, dark chocolate, some green vegetables and magnesium-rich waters. For the detail, portion by portion, see our ranking of magnesium-rich foods.
If you are considering a supplement, start with the lowest dose, read the actual amount of elemental magnesium on the label, and add it to that of any fortified or highly mineralised waters you drink: it is the total of added magnesium that counts towards the limit of 250 mg a day.
Who should be careful?
- Kidney failure: no magnesium supplement without medical advice.
- Older people taking magnesium-based laxatives or antacids long term, whose kidney function declines with age.
- Children: adult supplements are not suitable; doses should be discussed with the paediatrician.
- Treatments: antibiotics, bisphosphonates, thyroid hormones, see the table above.
To find out whether you are short of magnesium, and where to find it in food, see our guides magnesium: benefits and deficiency and magnesium-rich foods.
Frequently asked questions
What are the symptoms of too much magnesium?
Mostly diarrhoea, abdominal cramps and nausea. Severe forms, muscle weakness, low blood pressure, heart problems, mainly concern kidney failure or medication overdoses.
What is the maximum daily dose of magnesium?
EFSA sets 250 mg a day for magnesium from supplements, waters and fortified foods. Magnesium from food does not count.
Can you overdose on magnesium from food?
No, when the kidneys work normally: the excess is removed in the urine.
Does magnesium keep you awake?
No, it is not a stimulant. No official recommendation requires you to take it in the morning or the evening.
Does magnesium cause constipation?
No, it tends to have a laxative effect, especially as oxide, chloride or sulphate.
How do you quickly get rid of excess magnesium?
By stopping the supplement. If you have significant symptoms or kidney disease, see a doctor: they can monitor your blood magnesium and treat you.
Does magnesium help you sleep?
The evidence is weak: three small trials in older people suggest falling asleep about 17 minutes faster, with studies of limited quality.
Does magnesium relieve cramps?
According to the 2020 Cochrane review, it is unlikely to noticeably reduce night cramps in older people. During pregnancy, results are conflicting.
Can you take magnesium when pregnant?
Its effectiveness against cramps has not been shown: ask your midwife or doctor for advice, and stay under 250 mg a day of added magnesium.
What is the maximum dose of magnesium for a child?
According to EFSA, 250 mg a day of added magnesium from age 4, as for adults. Before age 4, no limit has been set: no supplement without a paediatrician’s advice.
Is Epsom salt dangerous?
Swallowed in large amounts or used as an enema, yes: serious, sometimes fatal poisonings have been reported, including in people with healthy kidneys. Do not take it by mouth without medical advice.
Should you monitor magnesium when taking a magnesium laxative?
In people who take high doses every day, for weeks, with reduced kidney function, studies recommend regular blood magnesium tests. Talk to your doctor.
Our sources
- EFSA, tolerable upper intake level for magnesium: 250 mg a day of added magnesium.
- Anses, nutritional references for vitamins and minerals, published 21 February 2025.
- Aal-Hamad AH et al. Hypermagnesemia in Clinical Practice. Medicina, 2023.
- Tosto F et al. Neurological manifestations of hypermagnesemia: a narrative review. Acta Neurologica Belgica, 2025.
- Costello R et al. Perspective: Call for Re-evaluation of the Tolerable Upper Intake Level for Magnesium Supplementation in Adults. Advances in Nutrition, 2023.
- Ciqual 2025 table (Anses): Hépar water.
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complement Med Ther, 2021 (PMID 33865376).
- Garrison SR et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev, 2020 (PMID 32956536).
- Luo L et al. Interventions for leg cramps in pregnancy. Cochrane Database Syst Rev, 2020 (PMID 33275278).
- EFSA. Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA), version 11, August 2025.
- Wakai E et al. Risk factors for the development of hypermagnesemia in patients prescribed magnesium oxide: a retrospective cohort study. J Pharm Health Care Sci, 2019 (PMID 30805197).
- Mori H et al. Clinical features of hypermagnesemia in patients with functional constipation taking daily magnesium oxide. J Clin Biochem Nutr, 2019 (PMID 31379418).
- Oda S et al. Risk factors analysis for hypermagnesemia with magnesium oxide. Yakugaku Zasshi, 2024 (PMID 39218658).
- Walker P, Parnell S, Dillon RC. Epsom salt ingestion leading to severe hypermagnesemia necessitating dialysis. J Emerg Med, 2020 (PMID 32389435).
- Shoaib Khan M, Zahid S, Ishaq M. Fatal hypermagnesemia: an acute ingestion of Epsom salt in a patient with normal renal function. Caspian J Intern Med, 2018 (PMID 30510660).
- Tofil NM, Benner KW, Winkler MK. Fatal hypermagnesemia caused by an Epsom salt enema: a case illustration. South Med J, 2005 (PMID 15759964).
