Magnesium
EVIDENCE: MODERATEAlso sold as: magnesium citrate, magnesium glycinate, magnesium oxide, mag
Magnesium helps more than 300 enzymes function. Human research includes blood pressure and migraine outcomes. Supplement forms differ in absorption and tolerability, so the form and elemental amount both matter.
Compiled by iSupplementReviews editorial team ·Updated 2026-10-13 · 6 sources
- Type
- Mineral / electrolyte
- Studied dose
- 200–400 mg/day elemental
- Best form
- citrate or glycinate — oxide is cheap but poorly absorbed
- Upper limit
- UL 350 mg/day supplemental (US; laxative threshold)
- Our rating
- MODERATE — Several human trials — limits in size, duration, or independence
What is magnesium?
Magnesium is an essential mineral used in more than 300 enzyme reactions. It supports energy production, muscles, nerves, bone, and blood-pressure regulation. About half the body’s store is in bone, and a normal blood result does not always establish adequate total stores.
The forms that matter — the key distinction in this category
| Form | Absorption | Notes |
|---|---|---|
| Oxide | Poor (~4% usable in comparisons) | Highest mg-per-pill, cheapest — the budget-label filler |
| Citrate | Good (Walker 2003: significantly > oxide) | Best-documented quality form |
| Glycinate/bisglycinate | Good | Gentlest on the gut — the “doesn’t cause diarrhea” pick |
| Chloride, lactate, malate | Reasonable | Mid-shelf options |
| Threonate | Marketed for brain uptake | Premium-priced, thin human data |
Two labels can both say “400 mg” and deliver wildly different absorbed doses. And watch the trick where “magnesium citrate 1,000 mg” is not 1,000 mg of magnesium (citrate is ~16% elemental by weight).
Where does it come from?
Leafy greens, nuts, seeds, legumes, whole grains, dark chocolate. The NIH estimates roughly half of US adults eat below the estimated average requirement. Refining strips magnesium from grains, so marginal intake is common even when frank deficiency isn’t.
What is magnesium claimed to do?
Sleep and “calm,” muscle cramps, blood pressure, blood sugar, migraine prevention, constipation, and general stress support. Several of these have real trials; a few are pure folk reputation.
What does the research show?
| Claim | Evidence | Dose studied | Verdict |
|---|---|---|---|
| Corrects inadequate intake | Strong (status data) | 200–400 mg/day | Supported |
| Migraine prevention | Trials + guideline acknowledgment | ~600 mg/day | Supported preventive |
| Blood pressure | Meta-analyses, small effect | ~300 mg/day | ~2 mmHg, in the insufficient |
| Insomnia (elderly) | Trial (Abbasi 2012) | 500 mg/day | Early positive |
| Blood-sugar/prediabetes support | Trials in low-Mg prediabetics | ~300–380 mg/day | Early positive |
| Night leg cramps | Cochrane (Garrison 2012) — negative | various | Largely unproven |
Migraine — the strongest claim
Peikert et al. (1996, Cephalalgia): migraine patients on ~600 mg/day for 12 weeks saw attack frequency fall ~42% vs ~16% on placebo, enough that headache-society guidance lists magnesium as a probably-effective preventive. It’s the claim with the best clinical footing.
Blood pressure — real but small
Dibaba et al. (2017, Hypertension meta): ~300 mg/day reduced systolic BP ~2.8 mmHg, specifically in magnesium-insufficient adults. The meta that included everyone showed the effect fading: a clean illustration that magnesium’s benefits concentrate in people who need it.
Sleep and blood sugar — early positives
Abbasi et al. (2012): 500 mg/day in elderly insomniacs improved insomnia scores, raised melatonin, and lowered cortisol; a real but small single-site trial. Prediabetes trials in magnesium-deficient patients show modest glucose improvements. Again, deficiency-first effects.
The debunked claim — cramps
Garrison et al. (2012, Cochrane): no benefit for unexplained night leg cramps, the single most common reason people buy magnesium. A folk remedy the trial record doesn’t support.
What doesn’t magnesium do?
It doesn’t sedate, doesn’t fix cramps for most people, and doesn’t move blood pressure in the already-sufficient. Oxide-heavy megadose pills mostly produce expensive stool.
What dose was studied?
| Goal | Dose | Form | Duration |
|---|---|---|---|
| Intake correction | 200–400 mg elemental | citrate-class | ongoing |
| Migraine prevention | ~600 mg | dicitrate | 12 weeks |
| Elderly insomnia | 500 mg | — | 8 weeks |
200–400 mg elemental is the therapeutic band; the upper limit for supplemental magnesium is 350 mg (the laxative threshold, not toxicity).
How and when to take it
Evening dosing suits the relaxation use; with food to buffer the gut effect; and separated 2–4 hours from interacting medications (see below), because magnesium binds several drugs in the gut.
Side effects
Diarrhea first, then nausea/cramping, dose- and form-dependent. True toxicity (low blood pressure, lethargy, cardiac effects) is essentially a kidney-disease or massive-dose scenario: healthy kidneys excrete the excess.
Drug interactions
- Quinolone & tetracycline antibiotics: binding blocks their absorption (separate 2–4 h)
- Levothyroxine: same mechanism (separate)
- Bisphosphonates: same mechanism
- Blood-pressure drugs: additive mild lowering
Deficiency — who’s at risk?
Older adults, type-2 diabetics, GI-disease patients, heavy alcohol users, and chronic acid-blocker or diuretic users. Frank deficiency is rare; chronic marginal insufficiency is common and mostly silent.
Who should not take magnesium?
Anyone with significant kidney impairment without physician supervision; people on interacting drugs who can’t space doses.
What the authorities say
NIH ODS sets the supplemental upper limit at 350 mg (the laxative threshold) and flags the medication-timing interactions; headache-society evidence reviews acknowledge magnesium among the better-supported non-drug migraine preventives, unusual institutional backing for a supplement claim.
What to know about magnesium
Check elemental magnesium, not just the weight of its salt. Cited supplemental ranges are commonly 200–400 mg, and forms differ in absorption and tolerability. A 50 mg amount contributes to intake but does not establish the same effects as larger study doses.
Frequently asked questions about Magnesium
Which form of magnesium is best absorbed?
Citrate and glycinate absorb best; Walker et al. (2003) found citrate significantly better absorbed than oxide. Oxide has the highest elemental magnesium per pill but the worst absorption, so a label can say 400 mg and deliver very little usable magnesium.
Does magnesium help with sleep?
Modestly, in some trials, mainly older adults or the magnesium-insufficient (Abbasi et al., 2012: 500 mg improved insomnia markers, melatonin, and cortisol in elderly subjects). It's a plausible relaxation aid, not a sedative.
Can magnesium lower blood pressure?
A small effect is real: meta-analyses (Dibaba et al., 2017) show ~2–3 mmHg reductions, concentrated in people who were magnesium-insufficient. Supporting player, not medication replacement.
Does magnesium help migraines?
It has the strongest preventive evidence of the bunch. Trials showed reduced attack frequency at ~600 mg/day, and headache-society guidance lists magnesium as a probably-effective migraine preventive.
Why does magnesium cause diarrhea?
Unabsorbed magnesium draws water into the intestine: the osmotic effect behind milk of magnesia and the reason the US supplemental upper limit is 350 mg. Poorly absorbed forms (oxide) trigger it at lower doses; glycinate is gentlest.
References
- [1]NIH Office of Dietary Supplements — Magnesium Fact Sheet for Health Professionals
- [2]Dibaba DT et al. — Magnesium supplementation and blood pressure in insufficient adults (Hypertension, 2017)
- [3]Walker AF et al. — Mg citrate vs oxide bioavailability (Magnes Res, 2003)
- [4]Abbasi B et al. — Magnesium for insomnia in the elderly, RCT (J Res Med Sci, 2012)
- [5]Peikert A et al. — Magnesium prophylaxis of migraine, RCT (Cephalalgia, 1996)
- [6]Garrison SR et al. — Magnesium for skeletal muscle cramps: Cochrane review (2012)
Products we reviewed containing Magnesium
Based on recorded labels or seller-described formulas. Inclusion does not establish a match to the strains, preparations or amounts studied here; check each review's disclosure limits.