A mineral in nuts, seeds, beans and greens that more than 300 enzyme systems need. As a supplement, best supported for constipation, blood pressure and migraine.
Ask a doctor or pharmacist first if you:
Magnesium is a mineral that the body needs for more than 300 enzyme systems, including those for muscles, nerves, blood sugar and blood pressure.[1] An adult body holds about 25 g, and half or more of it is in bone.[1]
Good food sources are green leafy vegetables, beans, nuts, seeds and whole grains.[1] Supplements sell it as magnesium oxide, citrate, chloride and other forms. It is also in some laxatives and antacids.[1]
Taken by mouth, magnesium has the best evidence for four uses:
Other expected benefits have weak support. For sleep, a 2026 review of 12 trials found inconsistent results with low to very low certainty.[8] A Cochrane review found magnesium unlikely to prevent leg cramps in older adults.[9] In athletes, a review found no gain in muscle strength or power.[10]
Many large magnesium trials tested it as a hospital medicine, not as a supplement. Magnesium sulphate lowered the risk of eclampsia (seizures) by 58% in 10,141 women with pre-eclampsia.[11] An infusion during heart surgery gave fewer heart attacks and rhythm problems in 250 patients with a thickened heart wall.[12] A magnesium sulphate drink cleaned the bowel before colonoscopy as well as the standard solution in 1,174 older adults.[13]
Magnesium from food is safe for healthy people, because the kidneys remove the extra in urine.[1] Supplements and medicines carry some risks:
People with kidney disease, or who take a medicine every day, should ask a doctor or pharmacist first.[1]
Magnesium is a mineral that more than 300 enzyme systems need, including those that control muscles, nerves, blood sugar and blood pressure.[1] An adult body holds about 25 g of it.[1]
Most of the body's magnesium is in bone and soft tissues. Bone holds 50 to 60% of the body's magnesium, and the blood serum less than 1%.[1]
Magnesium salts that the gut does not absorb hold water in the bowel by osmosis and speed up the gut. This is why large doses loosen stools and cause diarrhea.[1]
Each row is one benefit. The square shows the grade and the number of studies. Open a row to see the most trusted studies.
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In a 2025 review of 38 blood pressure trials, the daily dose was 82 to 637 mg of elemental magnesium, with a median of 365 mg.[3] The US recommended amount for adults is 400 to 420 mg a day for men and 310 to 320 mg for women, from food and supplements together.[1]
Blood pressure: a median of 365 mg a day in a 2025 review of 38 trials.[3] Migraine: 600 mg a day as trimagnesium dicitrate in a 12-week trial.[17] Constipation: 1.5 g of magnesium oxide a day in a 4-week trial.[18] Blood sugar: 300 mg a day as magnesium chloride for 16 weeks in a trial in people with type 2 diabetes and low blood magnesium.[1]
The US recommended amount is 80 mg a day at 1 to 3 years, 130 mg at 4 to 8 years and 240 mg at 9 to 13 years. At 14 to 18 years it is 410 mg for boys and 360 mg for girls. Adult men need 400 to 420 mg and adult women 310 to 320 mg. In pregnancy it is 350 to 400 mg, and when breastfeeding 310 to 360 mg, depending on age.[1] EFSA, the EU food safety authority, sets 350 mg a day for men and 300 mg for women, with no extra amount in pregnancy or when breastfeeding.[19]
Supplements contain magnesium oxide, citrate, chloride and other forms. The label shows the amount of magnesium itself (elemental magnesium), not the weight of the whole compound.[1] For example, 500 mg of magnesium oxide gives 300 mg of magnesium.[1] Forms that dissolve well in water, such as citrate and chloride, are absorbed more completely than oxide.[1]
Blood pressure trials in the 2025 review lasted at least 4 weeks, with a median of 12 weeks.[3] A 2016 review found that 1 month was enough to raise blood magnesium and lower blood pressure.[20] In a 2016 review of blood sugar trials, fasting glucose improved only in trials of 4 months or longer.[21]
The US upper limit for magnesium from supplements and medicines is 350 mg a day from age 9, also in pregnancy. It is 65 mg at 1 to 3 years and 110 mg at 4 to 8 years. Magnesium from food does not count.[1] The EU upper limit is 250 mg a day from age 4, for magnesium salts in supplements, water and fortified foods.[14] The usual migraine dose is above the US limit, and NIH ODS says it should be taken only under a health professional's supervision.[1] People with kidney disease should ask a doctor first.[1]
Most studies gave 250 to 500 mg a day, for 1 to 3 months.
The counts are study groups. A study group is one set of people in a study who took the same dose. One study can have several groups. These are amounts from studies, not advice for you.
85 of 265 study groups took magnesium with something else. This shows what studies gave together, not what works together.
What studies used when they gave magnesium for one goal, or to a group of people.
Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.
12 questions in 4 groups. Open one for the short answer; each has its own page with the full answer and sources.
Green leafy vegetables, beans and other legumes, nuts, seeds and whole grains. In general, foods with fiber provide magnesium.[1] Some examples:
Refined grains lose much of their magnesium when the germ and bran are removed. Tap, mineral and bottled water can add from 1 mg to more than 120 mg per liter, depending on the source.[1] The body absorbs about 30 to 40% of the magnesium in food.[1]
Deficiency with symptoms is uncommon in healthy people, because the kidneys pass less magnesium into urine when intake is low.[1] Low intake is common, though: in a 2013 to 2016 US survey, 48% of people got less than the average requirement from food and drinks.[1] These groups are more likely to run low:
Early signs of deficiency are loss of appetite, nausea, vomiting, tiredness and weakness. Later come numbness, tingling, muscle cramps, seizures and abnormal heart rhythms.[1] Severe deficiency can also lower blood calcium and potassium.[1] A blood test is the usual check, but the blood level says little about the magnesium in cells and bone.[1]
Possibly a little, but the evidence is weak. A 2026 review of 12 trials found inconsistent results, with low to very low certainty, and did not support magnesium as a routine treatment for insomnia.[8] In older adults with insomnia, 3 small trials found that people fell asleep about 17 minutes faster.[22]
A little. A 2025 review of 38 trials with 2,709 people found 2.81 mmHg lower systolic and 2.05 mmHg lower diastolic blood pressure than with a placebo.[3] The drop was larger in people with high blood pressure who took blood pressure medicines, and in people with low blood magnesium. In people with normal blood pressure it was not significant.[3]
It may make migraines less frequent. In 2012, US neurology and headache societies rated magnesium as probably effective for preventing migraine.[4] In a 2025 review, magnesium lowered the number of attacks and gave 1.66 fewer migraine days a month.[5]
The trials are small and do not all agree. In a 12-week trial in 81 adults, 600 mg a day as trimagnesium dicitrate cut attacks by 41.6%, against 15.8% with placebo.[17] Another trial in 69 adults, with 10 mmol twice a day, found no benefit and was stopped early.[23] A 2018 review graded magnesium as possibly effective.[24]
The usual migraine dose is above the US upper limit of 350 mg a day from supplements. NIH ODS says to take it only under a health professional's supervision.[1] Diarrhea was common: it affected 18.6% of people on 600 mg a day in one trial.[17] In the other trial, 45.7% on magnesium had mild side effects such as soft stools and diarrhea, against 23.5% on placebo.[23]
For older adults with night cramps, probably not. A 2020 Cochrane review found it unlikely that magnesium prevents muscle cramps in older adults in a way that matters.[9] For leg cramps in pregnancy, the trials conflict, and no trial has tested cramps during exercise.[9][25]
Slightly. A 2021 review of double-blind trials found that magnesium lowered fasting glucose in people with diabetes. In people at high risk, it improved glucose and insulin sensitivity.[6] In a 2026 review of 78 trials, fasting glucose was 3.60 mg/dL lower and HbA1c 0.15 percentage points lower. The authors called the effects modest.[7]
A 2016 review found a clear drop in fasting glucose only in trials that lasted 4 months or longer.[21] Single trials disagree. In people with type 2 diabetes and low blood magnesium, 300 mg a day as magnesium chloride for 16 weeks lowered glucose and HbA1c. In 50 people with type 2 diabetes on insulin, 369 mg a day as magnesium aspartate for 3 months did not change blood sugar control.[1]
The American Diabetes Association says the evidence is not enough to recommend magnesium for blood sugar control.[1] People who take diabetes medicines should ask a doctor or pharmacist first.[1]
Yes. Magnesium is a main ingredient of some laxatives, such as milk of magnesia.[1] Magnesium salts that the gut does not absorb hold water in the bowel by osmosis and loosen stools.[1]
A 2023 review pooled 2 trials of magnesium oxide in adults with chronic constipation. 68% improved on magnesium oxide, against 19% in the control groups. People had 3.72 more bowel movements a week, and softer stools.[2] In a 2021 trial in 90 adults, one group took 1.5 g of magnesium oxide a day for 28 days. 68.3% of them improved, about as many as with senna (69.2%), against 11.7% with placebo.[18]
A 2023 guideline of two US gastroenterology societies gives magnesium oxide a conditional recommendation for chronic constipation. Polyethylene glycol and some other medicines got a strong recommendation.[26]
Laxative doses can be well above the US upper limit of 350 mg a day, but part of the magnesium is not absorbed.[1] People with kidney disease can build up too much magnesium and should ask a doctor first.[1]
Possibly, but the evidence is poor. A 2017 review of 18 studies found that magnesium might ease anxiety in people prone to it, such as people with mild anxiety or premenstrual syndrome. The authors rated the quality of the evidence as poor.[27] Magnesium had no effect on anxiety after childbirth, and no study used a validated measure of stress.[27]
For low mood, a 2020 review found mixed results.[28] In one trial, 126 adults with mild to moderate depression took 248 mg of magnesium a day as magnesium chloride for 6 weeks. Their depression score fell by 6.0 points more than in the weeks without magnesium, and their anxiety score by 4.5 points.[29] The trial had no placebo, so people knew when they were taking magnesium.[29]
People who take antidepressants or another medicine every day should ask a doctor or pharmacist first.[1]
Some antibiotics and some osteoporosis medicines. NIH ODS gives these time gaps:
Other medicines change the body's magnesium level:
Some antacids and laxatives contain magnesium too, and the US upper limit counts magnesium from both supplements and medicines.[1] People who take a medicine every day should ask a doctor or pharmacist first.[1]
Pregnancy has its own recommended amount, and the same upper limit as for other adults. The US recommended amount in pregnancy is 350 to 400 mg a day from food and supplements together. The upper limit from supplements is 350 mg a day, the same as for other adults.[1] EFSA, the EU food safety authority, found no evidence that pregnancy raises the need, and sets 300 mg a day.[19]
A 2014 Cochrane review of 10 trials with 9,090 women found no clear effect of magnesium supplements on stillbirths and newborn deaths, small babies or pre-eclampsia. Only 2 of the trials were of high quality.[30] One analysis showed more newborn deaths with magnesium. This came mostly from one trial, and the difference went away when deaths from severe birth defects were left out.[30] A 2022 review of 7 trials found a lower risk of pre-eclampsia (risk ratio 0.76), but not in women at normal risk.[31]
For leg cramps in pregnancy, trial results conflict.[25]
Magnesium sulphate given by doctors for pre-eclampsia is a different, medical use. In 10,141 women it lowered the risk of eclampsia by 58%.[11]
Pregnant women should ask a doctor or pharmacist before taking more than 350 mg a day from supplements.[1]
Yes, but the differences are modest. In small studies, forms that dissolve well in water, such as citrate, chloride, lactate and aspartate, were absorbed more completely than magnesium oxide and sulfate.[1] A 2021 review of 14 studies found that all forms can keep normal magnesium levels in healthy people who are not low on it.[32]
