Magnesium is an essential dietary mineral. The body uses it as a cofactor for more than 300 enzyme systems, including those that make and use ATP, and it is needed for normal nerve, muscle and heart function. It comes from foods such as green leafy vegetables, whole grains and nuts, and it is sold in many supplement forms and in over-the-counter antacids and laxatives.
In fitness circles, magnesium is promoted for better sleep, fewer cramps, lower blood pressure and higher testosterone. Controlled trials support a small blood pressure reduction, mainly in people with hypertension or low magnesium. The evidence for sleep is weak and inconsistent, and the Cochrane review found no meaningful benefit for typical night-time leg cramps in older adults. Claims of a testosterone boost rest on observational data and one small uncontrolled study. The most important safety fact: the US upper limit of 350 mg/day applies to magnesium from supplements and drugs, not from food.
This page summarizes what the National Academies’ dietary reference report, regulators and clinical trials report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Type | Essential dietary mineral (electrolyte) |
| Body content | About 25 g in an adult; 50–60% in bone, about 1% outside cells |
| Adult RDA (US) | Men 400 mg/day (19–30 y), 420 mg/day (31+ y); women 310 mg/day (19–30 y), 320 mg/day (31+ y) |
| Upper limit (US) | 350 mg/day from supplements and drugs (not food), ages 9 and up |
| Upper limit (EU) | 250 mg/day from readily dissociable supplemental salts |
| Normal serum level | 0.75–0.95 mmol/L (1.8–2.3 mg/dL) |
| Doses in cited trials | 82–637 mg/day elemental magnesium (blood pressure trials); 250–520 mg/day in the sleep and cramp trials below |
| Half-life | No single value applies: blood levels are held in a narrow range by the kidneys and the bone and tissue stores |
| Common forms | Oxide, hydroxide, citrate, chloride, lactate, sulfate, glycinate, L-threonate and others |
| WADA status | Not on the 2026 Prohibited List |
What it is
Magnesium is the mineral, and every supplement delivers it as a salt or chelate bound to another molecule. The National Academies’ Institute of Medicine (IOM) report describes it as a required cofactor for over 300 enzyme systems. It is needed for both anaerobic and aerobic energy production, for the sodium-potassium pump, for DNA and RNA synthesis, and for vitamin D metabolism and action (IOM 1997). The same report notes that magnesium has been called “nature’s physiological calcium channel blocker”: during depletion, calcium inside cells rises, which can contribute to muscle cramps and vessel spasm.
Total body magnesium is about 25 g. Of this, 50–60% sits in bone, and about one-third of the bone fraction is exchangeable, acting as a reservoir. Only about 1% is outside cells, which is why a normal serum level does not rule out low total-body stores (IOM 1997).
Dietary reference intakes
The IOM set the US Recommended Dietary Allowances (RDA) from magnesium balance studies (IOM 1997):
| Group | RDA (mg/day) |
|---|---|
| Children 1–3 y | 80 |
| Children 4–8 y | 130 |
| Ages 9–13 y | 240 |
| Boys 14–18 y | 410 |
| Girls 14–18 y | 360 |
| Men 19–30 y | 400 |
| Men 31 y and older | 420 |
| Women 19–30 y | 310 |
| Women 31 y and older | 320 |
| Pregnancy 14–18 / 19–30 / 31–50 y | 400 / 350 / 360 |
| Lactation | Same as non-lactating women of the same age |
The Tolerable Upper Intake Level (UL) works differently from most nutrients:
- It applies only to non-food magnesium. The IOM found no adverse effects from magnesium naturally present in food, so the UL covers supplements, antacids and other drugs only.
- It is set at 350 mg/day for adolescents and adults, including pregnancy and lactation. The critical effect is diarrhea. The lowest dose reported to cause it was 360 mg/day, and because diarrhea is mild, obvious and reversible, the IOM applied an uncertainty factor of about 1.
- Children have a UL of 5 mg/kg/day; no UL was set for infants.
In Europe, the former Scientific Committee on Food set a lower UL of 250 mg/day for readily dissociable magnesium salts and magnesium oxide in supplements. EFSA has since set adequate intakes of 350 mg/day for men and 300 mg/day for women (EFSA NDA Panel 2024).
Supplement forms and elemental content
Labels can list either the weight of the whole salt or the weight of magnesium itself (“elemental magnesium”). The difference is large:
| Form | Elemental magnesium | Example and notes |
|---|---|---|
| Magnesium oxide | 60–61% | A 400 mg tablet provides 241.3 mg magnesium; sold OTC as an antacid (DailyMed). Poorly soluble. |
| Magnesium hydroxide | 42% | Milk of magnesia (antacid, laxative) |
| Magnesium citrate | 16% | Saline laxative solutions contain 290 mg magnesium per fl oz (DailyMed) |
| Magnesium chloride | 12% | 64 mg in a 535 mg sustained-release tablet |
| Magnesium lactate | 12% | Sustained-release tablets |
| Magnesium glycerophosphate | 12.4% | Found in combination tablets |
| Magnesium aspartate hydrochloride | 10% | Powder for solution |
| Magnesium sulfate | 10% | Epsom salts; intravenous drug in hospitals |
| Magnesium L-threonate | 7.2–8.3% | EFSA specification for the authorized novel food |
| Magnesium gluconate | 5% | 27 mg in a 500 mg tablet |
| Magnesium glycinate (bisglycinate) | No figure in the sources reviewed | Check the label for the elemental amount; the trial below used 250 mg elemental magnesium |
Figures are from a review in American Family Physician (Guerrera et al., AFP 2009), except glycerophosphate (Blancquaert et al., Nutrients 2019), L-threonate (EFSA NDA Panel 2024) and the product labels linked above. Doses in trials and in the RDA and UL refer to elemental magnesium.
How it works in the body
Absorption
According to the IOM, net absorption from a typical diet is about 50%. The fraction absorbed falls as intake rises: in balance studies, net absorption was about 40–60% at 380 mg/day but only 15–36% at 550–850 mg/day. Absorption happens along the whole gut, mostly in the distal small intestine. High-fiber diets, phytate and very high phosphate intake reduce it (IOM 1997).
A 2017 review concluded that the dose is the main factor controlling how much is absorbed. Several smaller doses through the day are absorbed better, as a fraction, than one large dose. The type of salt “appears less relevant than is often thought”: some studies found organic salts (such as citrate) slightly better absorbed than inorganic ones (such as oxide), and others did not (Schuchardt & Hahn, Curr Nutr Food Sci 2017).
Product formulation matters as well. A Belgian study tested 15 commercial supplements in a gut simulator and found very wide differences in how much magnesium dissolved and was absorbed. In 30 volunteers, a tablet combining oxide and glycerophosphate (196 mg magnesium) raised serum magnesium more than a pure oxide tablet with more than twice the magnesium (450 mg) (Blancquaert et al., Nutrients 2019):
| Measure | Oxide + glycerophosphate | Oxide only |
|---|---|---|
| Peak rise in serum magnesium | +6.2% | +4.6% |
| Area under the curve | 6.87 mM·min | 0.31 mM·min |
The oxide-glycerophosphate tablets were supplied by their manufacturer.
Kidney control
The kidney is the main regulator of body magnesium. It filters magnesium and reabsorbs most of it, with no tubular secretion. When intake is cut sharply, urinary magnesium drops to under 20 mg/day within 3–4 days. Alcohol and diuretics both increase urinary losses (IOM 1997).
Because the kidneys adjust excretion so tightly, the IOM notes that high dietary intake has not caused high blood magnesium in people without intestinal or kidney disease. It also means serum magnesium is a poor guide to total-body status, and no single elimination half-life describes a supplement dose.
Approved medical uses
Several magnesium salts are sold as over-the-counter drugs with FDA Drug Facts labels:
- magnesium oxide as an antacid for acid indigestion (DailyMed);
- magnesium citrate solution as a saline laxative for occasional constipation, at 6.5–10 fl oz in 24 hours for adults (DailyMed).
In hospitals, intravenous magnesium sulfate is used for eclampsia and certain arrhythmias (Guerrera et al., AFP 2009). Those uses are outside the scope of oral supplementation.
What the research shows
Blood pressure
This is the best-supported claim. Two large meta-analyses of randomized trials found small average reductions:
| Meta-analysis | Trials (participants) | Median dose | Median duration | Systolic BP | Diastolic BP |
|---|---|---|---|---|---|
| Zhang et al., Hypertension 2016 (double-blind, placebo-controlled only) | 34 (2,028) | 368 mg/day | 3 months | −2.00 mm Hg (95% CI 0.43–3.58 reduction) | −1.78 mm Hg (95% CI 0.73–2.82 reduction) |
| Argeros et al., Hypertension 2025 | 38 (2,709) | 365 mg/day (range 82.3–637) | 12 weeks | −2.81 mm Hg (95% CI −4.32 to −1.29) | −2.05 mm Hg (95% CI −3.23 to −0.88) |
The 2025 analysis found that the effect depended on who was treated:
- People with hypertension on blood pressure medication: systolic −7.68 mm Hg, diastolic −2.96 mm Hg.
- People with low serum magnesium (hypomagnesemia): systolic −5.97 mm Hg, diastolic −4.75 mm Hg.
- People with normal blood pressure: no statistically significant change.
It found no dose-response relationship and high heterogeneity between trials, so the authors advised caution. The 2016 analysis reported that serum magnesium rose by 0.05 mmol/L with supplementation.
Sleep
Evidence for sleep is limited and of low quality:
| Study | Design and population | Dose | Main result |
|---|---|---|---|
| Mah & Pitre, BMC Complement Med Ther 2021 | Meta-analysis of 3 RCTs; 151 older adults with insomnia | Various oral doses | Fell asleep 17.36 min faster (95% CI 7.44–27.27 min); total sleep time +16.06 min, not significant; low to very low quality evidence |
| Schuster et al., Nat Sci Sleep 2025 | RCT; 155 adults aged 18–65 with poor sleep | 250 mg/day elemental magnesium as bisglycinate | Insomnia Severity Index −3.9 vs −2.3 with placebo at week 4 (p = 0.049); small effect (Cohen’s d = 0.2) |
| Hausenblas et al., Sleep Med X 2024 | RCT; 80 adults aged 35–55 with sleep complaints; 21 days | 1 g/day magnesium L-threonate | Better wearable (Oura ring) deep and REM sleep scores and some questionnaire items vs placebo. Several authors work for the ingredient supplier. |
| Lopresti & Smith, Front Nutr 2026 | RCT; 100 adults aged 18–45 with poor sleep; 6 weeks | 2 g/day magnesium L-threonate | Improved self-rated sleep-related impairment; no difference in sleep disturbance or in wearable sleep measures. Funded by the ingredient’s supplier. |
A 2026 systematic review of 12 randomized trials found inconsistent results across questionnaires, EEG and actigraphy. The certainty of evidence was low to very low. The authors concluded that current evidence “does not support oral magnesium as a routine treatment for insomnia,” while modest subjective benefits may occur in some adults (Lopresti et al., J Diet Suppl 2026). In the bisglycinate trial, exploratory analyses suggested larger benefits in people with low dietary magnesium intake.
Muscle cramps
The Cochrane review pooled 11 randomized trials with 735 participants (Garrison et al., Cochrane 2020). For idiopathic cramps, mostly night-time leg cramps in older adults, magnesium did not beat placebo:
| Outcome at 4 weeks | Magnesium vs placebo | Certainty |
|---|---|---|
| Cramps per week | −0.18 (95% CI −0.84 to 0.49) | Moderate |
| % change in cramps per week | −9.59% (95% CI −23.14% to 3.97%) | Moderate |
| People with a 25% or greater reduction | RR 1.04 (95% CI 0.84–1.29) | High |
The authors concluded that magnesium is unlikely to give clinically meaningful cramp prevention in older adults. For pregnancy-associated leg cramps, the trials conflicted and were at high risk of bias. The review found no randomized trials for exercise-associated cramps.
Later trials agree:
- Magnesium oxide, 520 mg/day elemental magnesium at bedtime for 4 weeks (94 adults with nocturnal leg cramps): cramps fell by 3.41 per week vs 3.03 with placebo (P = .67). The authors attributed most of the improvement to a placebo effect (Roguin Maor et al., JAMA Intern Med 2017).
- Three-arm trial in 121 adults aged 50–85: magnesium did not differ from placebo (adjusted difference −0.20 cramps/week, 95% CI −1.49 to 1.09), while compression stockings reduced cramps (−1.43, 95% CI −2.36 to −0.50) (Kuusipalo et al., Trials 2026).
- Pregnancy: a meta-analysis of 4 RCTs with 332 women found no reduction in cramp frequency (WMD −0.47, 95% CI −1.14 to 0.20) (Liu et al., Taiwan J Obstet Gynecol 2021).
Testosterone
The testosterone claim is weakly supported:
- Observational data. In 399 men aged 65 and older from the Italian InCHIANTI cohort, higher serum magnesium was independently associated with higher total testosterone and IGF-1 (Maggio et al., Int J Androl 2011). An association in older men does not show that supplements raise testosterone.
- One small intervention study. Sedentary men and tae kwon do athletes took 10 mg/kg/day of magnesium for 4 weeks, and free and total testosterone rose. The comparison group of athletes received no supplement rather than a placebo, and the abstract does not report group sizes (Cinar et al., Biol Trace Elem Res 2011).
- ZMA trials. ZMA, a zinc, magnesium aspartate and vitamin B6 product, is marketed for testosterone. In 42 resistance-trained men over 8 weeks, ZMA did not change anabolic or catabolic hormones, body composition or strength vs placebo (Wilborn et al., JISSN 2004). In 14 exercising men with adequate zinc intake, ZMA did not change serum total or free testosterone (Koehler et al., Eur J Clin Nutr 2009). See Zinc for that mineral’s evidence.
We found no placebo-controlled trial showing that magnesium alone raises testosterone in men whose magnesium intake is already adequate.
Side effects and risks
Diarrhea and stomach upset
Diarrhea is the first and most common effect of excess supplemental magnesium, because unabsorbed magnesium salts draw water into the gut. This is the basis of the 350 mg/day UL and of magnesium’s use as a laxative (IOM 1997). In the Cochrane cramp review, mostly gastrointestinal side effects occurred in 11–37% of people on oral magnesium, compared with 10–14% on placebo. Serious adverse events did not differ from placebo (Garrison et al., Cochrane 2020).
Kidney disease and high blood magnesium
People with impaired kidney function are at greatest risk of magnesium toxicity. High blood magnesium (hypermagnesemia) is most often seen when kidney impairment is combined with large non-food intakes such as antacids. Serious neurological and heart symptoms generally appear only at serum levels above 2–3.5 mmol/L (4.8–8.4 mg/dL) (IOM 1997). The OTC magnesium oxide and citrate labels tell people with kidney disease to ask a doctor before use.
Interactions
- Quinolone antibiotics. The ciprofloxacin label says to take the antibiotic at least 2 hours before or 6 hours after magnesium- or aluminum-containing antacids and supplements. Such antacids can cut ciprofloxacin’s bioavailability by as much as 90% (DailyMed).
- Other drugs. The magnesium citrate laxative label advises taking it 2 or more hours before or after other drugs (DailyMed).
- Proton pump inhibitors (PPIs). PPI labels warn that low magnesium has been reported rarely after at least 3 months of treatment, in most cases after a year. Serious effects include tetany, arrhythmias and seizures, and most cases needed both magnesium replacement and stopping the PPI (Prilosec label, DailyMed).
- Diuretics and alcohol increase urinary magnesium loss (IOM 1997).
Product quality
In the Belgian study of 15 commercial products, dissolution and absorption varied widely, and some tablets contained more elemental magnesium per tablet than the US and EU upper limits (Blancquaert et al., Nutrients 2019). Label elemental content, not salt weight, is the figure that compares with the RDA and UL.
Legal status and use in sport
Magnesium salts are sold as dietary supplements and as OTC antacids and laxatives. Magnesium does not appear on the WADA 2026 Prohibited List. Combination products may contain other ingredients, so the full label matters for tested athletes.
Key takeaways
- An essential mineral with clear requirements. The US RDA is 400–420 mg/day for men and 310–320 mg/day for women, mostly from food.
- The upper limit is for supplements only. 350 mg/day of non-food magnesium (250 mg/day in the EU), set because higher doses cause diarrhea. Food magnesium has no UL.
- Check elemental content. Magnesium oxide is about 60% magnesium, citrate about 16% and gluconate about 5%. Dose and formulation affect absorption more than the salt name suggests.
- Blood pressure: small, real effect. About 2–3 mm Hg systolic on average, larger in people with hypertension or low magnesium, and no significant effect in people with normal blood pressure.
- Sleep, cramps and testosterone: weak or negative evidence. Sleep trials are small and inconsistent, high-quality trials found no benefit for typical leg cramps, and no placebo-controlled trial shows magnesium alone raises testosterone in replete men.
- Kidney disease and drug timing matter. Impaired kidneys raise the risk of high blood magnesium, and magnesium blocks absorption of drugs such as ciprofloxacin.
Sources
- Institute of Medicine, Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. 6 Magnesium. In: Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academies Press; 1997. doi:10.17226/5776. NAP.
- EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA), Turck D, Bohn T, et al. Safety of magnesium l-threonate as a novel food pursuant to regulation (EU) 2015/2283 and bioavailability of magnesium from this source in the context of Directive 2002/46/EC. EFSA J. 2024;22(3):e8656. PMC.
- Guerrera MP, Volpe SL, Mao JJ. Therapeutic uses of magnesium. Am Fam Physician. 2009;80(2):157–162. PubMed.
- Westminster Pharmaceuticals. Magnesium oxide 400 mg tablet, Drug Facts label. DailyMed.
- Nice-Pak Products. Citroma (magnesium citrate) oral solution, Drug Facts label. DailyMed.
- Blancquaert L, Vervaet C, Derave W. Predicting and testing bioavailability of magnesium supplements. Nutrients. 2019;11(7):1663. PubMed.
- Schuchardt JP, Hahn A. Intestinal absorption and factors influencing bioavailability of magnesium—an update. Curr Nutr Food Sci. 2017;13(4):260–278. PubMed.
- 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;68(2):324–333. PubMed.
- Argeros Z, Xu X, Bhandari B, et al. Magnesium supplementation and blood pressure: a systematic review and meta-analysis of randomized controlled trials. Hypertension. 2025;82(11):1844–1856. PubMed.
- Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review & meta-analysis. BMC Complement Med Ther. 2021;21(1):125. PubMed.
- Schuster J, Cycelskij I, Lopresti A, Hahn A. Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomized, placebo-controlled trial. Nat Sci Sleep. 2025;17:2027–2040. PubMed.
- Hausenblas HA, Lynch T, Hooper S, et al. Magnesium-L-threonate improves sleep quality and daytime functioning in adults with self-reported sleep problems: a randomized controlled trial. Sleep Med X. 2024;8:100121. PubMed.
- Lopresti AL, Smith SJ. The effects of magnesium L-threonate (Magtein) on cognitive performance and sleep quality in adults: a randomised, double-blind, placebo-controlled trial. Front Nutr. 2026;12:1729164. PubMed.
- Lopresti AL, Smith SJ, Drummond PD. Magnesium supplementation for sleep in adults: a systematic review of randomized controlled trials. J Diet Suppl. 2026;23(5):553–581. PubMed.
- Garrison SR, Korownyk CS, Kolber MR, et al. Magnesium for skeletal muscle cramps. Cochrane Database Syst Rev. 2020;9(9):CD009402. PubMed.
- Roguin Maor N, Alperin M, Shturman E, et al. Effect of magnesium oxide supplementation on nocturnal leg cramps: a randomized clinical trial. JAMA Intern Med. 2017;177(5):617–623. PubMed.
- Kuusipalo A, Laitila J, Lehtonen E, et al. Secondary prevention of leg cramps using compression stockings or magnesium supplements: a three-arm randomized clinical trial. Trials. 2026;27(1):216. PubMed.
- Liu J, Song G, Zhao G, Meng T. Effect of oral magnesium supplementation for relieving leg cramps during pregnancy: a meta-analysis of randomized controlled trials. Taiwan J Obstet Gynecol. 2021;60(4):609–614. PubMed.
- Maggio M, Ceda GP, Lauretani F, et al. Magnesium and anabolic hormones in older men. Int J Androl. 2011;34(6 Pt 2):e594–e600. PubMed.
- Cinar V, Polat Y, Baltaci AK, Mogulkoc R. Effects of magnesium supplementation on testosterone levels of athletes and sedentary subjects at rest and after exhaustion. Biol Trace Elem Res. 2011;140(1):18–23. PubMed.
- Wilborn CD, Kerksick CM, Campbell BI, et al. Effects of zinc magnesium aspartate (ZMA) supplementation on training adaptations and markers of anabolism and catabolism. J Int Soc Sports Nutr. 2004;1(2):12–20. PubMed.
- Koehler K, Parr MK, Geyer H, et al. Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement. Eur J Clin Nutr. 2009;63(1):65–70. PubMed.
- Hikma Pharmaceuticals. Ciprofloxacin tablets, prescribing information. DailyMed.
- Covis Pharma. Prilosec (omeprazole magnesium) for delayed-release oral suspension, prescribing information. DailyMed.
- World Anti-Doping Agency. The 2026 Prohibited List. WADA 2026 Prohibited List.