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Research · Supplements

Magnesium

Pooled trials find magnesium lowers blood pressure by about 2 mmHg. Results on insulin resistance markers are mixed. It did not reduce nocturnal leg cramps in older adults. Sleep and muscle strength data are sparse and low certainty. Diarrhea and other gut effects are the most common side effects. Laxative-dose magnesium has caused fatal hypermagnesemia.

Add to Bio HackChecked 2026-11-09
Status
Dietary supplement in the US. Magnesium salts are also sold as over-the-counter laxatives and antacids.
Also called
magnesium glycinate, magnesium bisglycinate, magnesium citrate, magnesium oxide, magnesium threonate, magnesium malate, magnesium chloride, ZMA, Epsom salt
Taken for
sleep, muscle cramps, blood pressure, blood sugar, muscle strength, recovery, stress, anxiety, constipation, period pain, PMS

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help3

Reported risks4

What people take it for, and what was found

Shown to help3

Strong

Blood pressure

Shown to lower blood pressure about 2 mmHg systolic and 2 mmHg diastolic, with larger drops of about 4 mmHg in people with insulin resistance or chronic disease.

The numbers and sources
Effect
Across 34 double-blind trials (2,028 participants), a median 368 mg a day for a median 3 months lowered systolic pressure by 2.00 mmHg (95% CI 0.43 to 3.58) and diastolic by 1.78 mmHg (95% CI 0.73 to 2.82) [1]. In 11 trials of people with insulin resistance, prediabetes or other chronic disease (543 participants), systolic pressure fell by 4.18 mmHg and diastolic by 2.27 mmHg (SMD -0.20 and -0.27) [2].
Population
Normotensive and hypertensive adults [1]; adults with preclinical or chronic disease given 365 to 450 mg a day for 1 to 6 months [2].
Sources
[1], [2]
Caveats
Residual heterogeneity remained after stratification in [1]. Effects in [2] are in people with existing disease.
Limited

Sleep

Small trials found sleep onset about 17 minutes faster in older adults with insomnia, with no significant change in total sleep. Quality was rated low.

The numbers and sources
Effect
In 3 RCTs (151 older adults), sleep onset was 17.36 minutes shorter on magnesium than placebo (95% CI -27.27 to -7.44). Total sleep time rose by 16.06 minutes, which was not statistically significant [7].
Population
Older adults with insomnia in three countries [7].
Sources
[7], [8]
Caveats
All three trials were at moderate to high risk of bias and the evidence was rated low to very low quality [7]. A 2026 systematic review of 12 RCTs in adults could not pool them. Findings were inconsistent across self-reported sleep, EEG, actigraphy and wearable measures, and certainty was low to very low [8].
LimitedStudied in women

Period pain

Small trials found magnesium relieved period pain more than placebo and cut the need for extra pain medicine, in a 2001 review.

Compared with placebo [18]

The numbers and sources
Effect
In three small trials, magnesium gave more pain relief than placebo, and less additional pain medication was needed. The number of adverse effects did not differ [18].
Population
Women with primary dysmenorrhea in three small randomized trials [18].
Sources
[18]
Caveats
The review is from 2001 and its abstract gives no pooled size of the effect. Doses and schedules varied between trials, and the authors could not name a dose or schedule from them [18].

Mixed results3

Moderate

Blood sugar and insulin resistance

Mixed results: most reviews found lower insulin resistance but disagreed on fasting glucose, and one review in people with diabetes found no significant change.

The numbers and sources
Effect
One meta-analysis found magnesium lowered HOMA-IR (WMD -0.67, 95% CI -1.20 to -0.14) but not fasting glucose (WMD -0.20 mmol/L, 95% CI -0.45 to 0.05) or HbA1c overall. Trials of 4 months or longer showed lower fasting glucose and HOMA-IR [3]. A 2021 meta-analysis of double-blind trials reported lower fasting glucose in people with diabetes and improved glucose and insulin-sensitivity markers in people at high risk [4]. A 2026 meta-analysis of 78 RCTs found lower HOMA-IR (WMD -0.48, 95% CI -0.79 to -0.18), fasting glucose (WMD -3.60 mg/dL) and HbA1c (WMD -0.15%) [5]. A 2026 meta-analysis of 15 RCTs (1,085 people with diabetes or prediabetes) found no significant change in insulin (MD -1.73) or HOMA-IR (MD -0.74, 95% CI -1.58 to 0.09). Baseline insulin and HOMA-IR modified the effect [6].
Population
People with and without diabetes [3][5]; people with or at high risk of diabetes [4][6].
Sources
[3], [4], [5], [6]
Caveats
The sources disagree on fasting glucose and on HOMA-IR in people with diabetes. The 2021 abstract does not report effect sizes [4]. The authors of [5] rated certainty as variable across outcomes.
Limited

Constipation

Limited evidence: magnesium oxide improved stool frequency and consistency in about half of small studies in functional constipation.

The numbers and sources
Effect
A 2026 systematic review of 7 studies (690 people, 5 of them RCTs) found better stool frequency than the comparator in 4 studies and better stool consistency in 4. Both studies that used a validated constipation quality-of-life tool found between-group improvement. No serious adverse events were reported [9].
Population
Infants, children and adults with functional constipation. Magnesium oxide was the most common form in adults [9].
Sources
[9]
Caveats
Narrative synthesis because of heterogeneity, certainty not formally graded, small samples and confounded interventions. Findings apply to magnesium oxide [9].
LimitedStudied in women

PMS symptoms

Mixed results: in small trials, magnesium eased premenstrual fluid retention in the second month but did not change mood symptoms on its own.

Compared with placebo [19][20]; vitamin B6 [20]; placebo or other nutritional interventions across the trials reviewed [21]

The numbers and sources
Effect
In a crossover trial of 200 mg a day, no symptom group differed from placebo in the first month. In the second month, fluid retention symptoms (weight gain, swelling, breast tenderness, bloating) fell more than on placebo (p = 0.009) [19]. In a second crossover trial, magnesium, vitamin B6, both together and placebo did not differ overall, while magnesium plus vitamin B6 lowered anxiety-related symptoms (p = 0.040) [20]. A review of 31 RCTs found insufficient evidence for magnesium on psychological PMS symptoms, and a crossover trial of 54 women found no significant effect of 200 mg a day over 2 months [21].
Population
38 women [19]; 44 women, mean age 32 [20]; 31 RCTs with 3,254 women aged 15 to 50 [21].
Sources
[19], [20], [21]
Caveats
Trials were small and lasted one or two cycles. Only 1 of the 31 trials in the review had a low risk of bias [21]. The authors of [20] judged absorption from magnesium oxide poor.

Not shown to help3

Moderate

Muscle cramps

Not shown to reduce idiopathic leg cramps in older adults. Pregnancy cramp trials conflicted, and none tested exercise cramps.

The numbers and sources
Effect
For idiopathic cramps, mostly nocturnal leg cramps in adults aged about 62 to 69, magnesium did not change the percentage change in cramps per week at 4 weeks (MD -9.59%, 95% CI -23.14% to 3.97%) or the number of cramps per week (MD -0.18, 95% CI -0.84 to 0.49). The share with a 25% or better reduction did not differ (RR 1.04, 95% CI 0.84 to 1.29, high certainty) [10].
Population
11 trials, 735 people, including pregnancy-associated and idiopathic cramps [10].
Sources
[10]
Caveats
Pregnancy cramp trials were conflicting and could not be pooled. No RCT tested exercise-associated cramps [10].
Limited

Muscle strength and performance

Limited evidence: no significant change in strength or power across trials. One small trial in exercisers found lower VO2max and sprint power on magnesium.

The numbers and sources
Effect
Across 14 RCTs, magnesium did not significantly change isokinetic peak torque (WMD 0.87, 95% CI -1.43 to 3.18), muscle strength (WMD 0.87, 95% CI -0.12 to 1.86) or muscle power (WMD 3.28, 95% CI -14.94 to 21.50). Benefits appeared more pronounced in older adults and people with alcoholism than in athletes [11].
Population
215 athletes or active people, 95 untrained adults, and 232 older adults or people with alcoholism [11].
Sources
[11], [12]
Caveats
Fixed-effects pooling across mixed populations and outcomes. In a 2025 crossover RCT of 15 regular exercisers, 600 mg a day of magnesium chloride for 9 days lowered VO2max (44.4 vs 41.3 mL/kg/min, p = 0.005) and 30 second sprint power (439 vs 415 W, p = 0.03) against placebo, with no change in a 10 km time trial [12].
Limited

Recovery and muscle soreness

One trial found a topical magnesium gel did not differ from a placebo gel on soreness or strength after downhill running.

The numbers and sources
Effect
A topical magnesium gel applied to both thighs before and after 40 minutes of downhill running did not differ from a placebo gel on muscle soreness, knee extensor strength, creatine kinase or interleukin-6 at 24 or 48 hours [13].
Population
35 healthy active adults, double-blind parallel RCT [13].
Sources
[13]
Caveats
One small trial of one commercial gel. No trial of oral magnesium on recovery was located in this search.

Doses studied

Blood pressure trials used a median 368 mg a day [1] and 365 to 450 mg of elemental magnesium a day [2]. The blood pressure review modeled 300 mg a day or 1 month as enough to raise serum magnesium [1]. Sleep trials used under 1 g up to three times a day [7].

Risks

Reported risks4

ModerateVery common

Diarrhea and other gut effects

Diarrhea and other gut effects were reported in 11 to 37% on oral magnesium against 10 to 14% on control in cramp trials.

The numbers and sources
How common
Very common: more than 1 in 10 people.
Effect
Across cramp trials, oral magnesium was linked mainly to gastrointestinal effects such as diarrhea, reported in 11% (10% on control) to 37% (14% on control) of participants. Minor adverse events were more frequent than placebo (RR 1.51, 95% CI 0.98 to 2.33, low certainty). Major adverse events were 2 of 72 on magnesium and 3 of 68 on placebo [10].
Population
Pooled cramp RCTs [10].
Sources
[10]
Caveats
Adverse event counts come from small trials.
LimitedVery common

Hypermagnesemia at laxative doses

Limited evidence: high blood magnesium was found in 16.6% of tested laxative users, tied to advanced kidney disease and over 1,000 mg a day. One death was reported.

The numbers and sources
How common
Very common: more than 1 in 10 people.
Effect
Among 193 patients on daily magnesium oxide for constipation whose levels were measured, 16.6% had high serum magnesium and 5.2% had hypermagnesemia. Stage 4 kidney disease and doses above 1,000 mg a day were associated factors [14]. A 53-year-old woman with normal kidney function on regular magnesium laxatives reached 10.8 mg/dL and died [15].
Population
Patients with functional constipation, retrospective cross-sectional [14]; one case report [15].
Sources
[14], [15]
Caveats
Laxative doses exceed most supplement doses. Only 8.9% of the 2,176 patients in [14] had a level measured.
LimitedStudied in menHow often is not known

Interaction with ciprofloxacin

Small trials found an aluminum and magnesium antacid taken up to 4 hours before ciprofloxacin cut its absorption. Taken 6 hours before or 2 hours after, it did not.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In healthy men, an aluminum and magnesium antacid taken 5 to 10 minutes, 2 hours or 4 hours before ciprofloxacin left 15.1%, 23.2% and 70% of its relative bioavailability. Taken 6 hours before or 2 hours after, it did not change absorption [16].
Population
Healthy male volunteers in crossover studies [16].
Sources
[16]
Caveats
The antacid combined aluminum and magnesium salts, so the share due to magnesium alone is not separated.
LimitedHow often is not known

Lower levothyroxine absorption

One trial found magnesium aspartate lowered levothyroxine absorption 12% in healthy adults, while the 7% drop with magnesium citrate was not significant.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Taken with 1 mg of levothyroxine, magnesium aspartate lowered thyroxine exposure (AUC) by 12% (GMR 0.88, 95% CI 0.81 to 0.95). Magnesium citrate lowered it by 7%, which was not statistically significant (GMR 0.93, 95% CI 0.86 to 1.01) [17].
Population
15 healthy euthyroid adults, open-label randomized crossover [17].
Sources
[17]
Caveats
Single doses over 6 hours in people without thyroid disease. Effects on TSH in treated patients were not measured.

Claims tested and not found

  1. That magnesium prevents night leg cramps in older adults. Cramp frequency did not differ from placebo at 4 weeks [10].
  2. That magnesium raises strength in athletes. Benefits were not apparent in athletes and physically active people [11].
  3. That magnesium gel on the skin speeds recovery after exercise. Soreness and muscle damage markers did not differ from placebo gel [13].

Sources

  1. Zhang X, Li Y, Del Gobbo LC, et al. Effects of Magnesium Supplementation on Blood Pressure: A Meta-Analysis of Randomized Double-Blind Placebo-Controlled Trials. Hypertension. 2016. https://doi.org/10.1161/HYPERTENSIONAHA.116.07664
  2. Dibaba DT, Xun P, Song Y, et al. The effect of magnesium supplementation on blood pressure in individuals with insulin resistance, prediabetes, or noncommunicable chronic diseases: a meta-analysis of randomized controlled trials. American Journal of Clinical Nutrition. 2017. https://doi.org/10.3945/ajcn.117.155291
  3. Simental-Mendía LE, Sahebkar A, Rodríguez-Morán M, et al. A systematic review and meta-analysis of randomized controlled trials on the effects of magnesium supplementation on insulin sensitivity and glucose control. Pharmacological Research. 2016. https://doi.org/10.1016/j.phrs.2016.06.019
  4. Veronese N, Dominguez LJ, Pizzol D, et al. Oral Magnesium Supplementation for Treating Glucose Metabolism Parameters in People with or at Risk of Diabetes: A Systematic Review and Meta-Analysis of Double-Blind Randomized Controlled Trials. Nutrients. 2021. https://doi.org/10.3390/nu13114074
  5. Mohammadi S, Palermo A, Ojani P, et al. Comprehensive Effects of Magnesium Supplementation on Cardiometabolic Risk Factors: A Systematic Review and Dose-Response Meta-Analysis. Nutrients. 2026. https://doi.org/10.3390/nu18152435
  6. Amiri A, Seighali F, Gholami-Chahkand MS, et al. Oral magnesium supplements and insulin resistance in individuals with diabetes and pre-diabetes: an updated systematic review and meta-analysis of randomized controlled trials. BMC Nutrition. 2026. https://doi.org/10.1186/s40795-026-01424-y
  7. Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a Systematic Review & Meta-Analysis. BMC Complementary Medicine and Therapies. 2021. https://doi.org/10.1186/s12906-021-03297-z
  8. Lopresti AL, Smith SJ, Drummond PD. Magnesium Supplementation for Sleep in Adults: A Systematic Review of Randomized Controlled Trials. Journal of Dietary Supplements. 2026. https://doi.org/10.1080/19390211.2026.2719670
  9. Kadhem H, Alasfoor W, Ali MS, et al. Efficacy of Magnesium Supplementation in Functional Constipation: A Systematic Review. Cureus. 2026. https://doi.org/10.7759/cureus.116715
  10. Garrison SR, Korownyk CS, Kolber MR, et al. Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews. 2020. https://doi.org/10.1002/14651858.CD009402.pub3
  11. Wang R, Chen C, Liu W, et al. The effect of magnesium supplementation on muscle fitness: a meta-analysis and systematic review. Magnesium Research. 2017. https://doi.org/10.1684/mrh.2018.0430
  12. Bomar MC, Ewell TR, Brown RL, et al. Short-Term Magnesium Supplementation Has Modest Detrimental Effects on Cycle Ergometer Exercise Performance and Skeletal Muscle Mitochondria and Negligible Effects on the Gut Microbiota: A Randomized Crossover Clinical Trial. Nutrients. 2025. https://doi.org/10.3390/nu17050915
  13. Coates AM, Patel DV, Binet ER, et al. No Effect of Topical Application of a Commercial Magnesium Gel on Exercise Recovery in Active Individuals. International Journal of Sport Nutrition and Exercise Metabolism. 2025. https://doi.org/10.1123/ijsnem.2025-0034
  14. Mori H, Suzuki H, Hirai Y, et al. Clinical features of hypermagnesemia in patients with functional constipation taking daily magnesium oxide. Journal of Clinical Biochemistry and Nutrition. 2019. https://doi.org/10.3164/jcbn.18-117
  15. Bokhari SR, Siriki R, Teran FJ, et al. Fatal Hypermagnesemia Due to Laxative Use. American Journal of the Medical Sciences. 2018. https://doi.org/10.1016/j.amjms.2017.08.013
  16. Nix DE, Watson WA, Lener ME, et al. Effects of aluminum and magnesium antacids and ranitidine on the absorption of ciprofloxacin. Clinical Pharmacology and Therapeutics. 1989. https://doi.org/10.1038/clpt.1989.207
  17. Attinger MC, von Felten S, Rodrigues CL, et al. Single Center, Open-Label, Randomized Crossover Trial on Drug-Drug Interactions of Levothyroxine/Magnesium-Citrate and Levothyroxine/Magnesium-Aspartate in Healthy Subjects. The ThyroMag Trial. Clinical and Translational Science. 2025. https://doi.org/10.1111/cts.70409
  18. Proctor ML, Murphy PA. Herbal and dietary therapies for primary and secondary dysmenorrhoea. Cochrane Database of Systematic Reviews. 2001. https://doi.org/10.1002/14651858.cd002124
  19. Walker AF, De Souza MC, Vickers MF, et al. Magnesium supplementation alleviates premenstrual symptoms of fluid retention. Journal of Women's Health. 1998. https://doi.org/10.1089/jwh.1998.7.1157
  20. De Souza MC, Walker AF, Robinson PA, Bolland K. A synergistic effect of a daily supplement for 1 month of 200 mg magnesium plus 50 mg vitamin B6 for the relief of anxiety-related premenstrual symptoms: a randomized, double-blind, crossover study. Journal of Women's Health & Gender-Based Medicine. 2000. https://doi.org/10.1089/152460900318623
  21. Robinson J, Ferreira A, Iacovou M, Kellow NJ. Effect of nutritional interventions on the psychological symptoms of premenstrual syndrome in women of reproductive age: a systematic review of randomized controlled trials. Nutrition Reviews. 2025. https://doi.org/10.1093/nutrit/nuae043

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