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Also: magnesium citrate · magnesium oxide · magnesium chloride · magnesium malate · magnesium L-threonate · mag
Four separate measurements, never averaged. Independent evidence counts only studies with no sponsor attached. Methodology version v2.0-2026-10 · how we grade evidence
Claimed to improve sleep, reduce anxiety and stress, prevent muscle cramps, lower blood pressure, improve glycaemic control, reduce migraine and support "300+ enzymatic reactions". The two claims with Cochrane-level or meta-analytic tests came out small and null respectively: blood pressure fell 2.00 mmHg systolic (95% CI 0.43–3.58) and 1.78 mmHg diastolic (0.73–2.82) across 34 double-blind trials, roughly a tenth of what a first-line antihypertensive achieves, and Cochrane concluded it is "unlikely that magnesium supplementation provides clinically meaningful cramp prophylaxis to older adults" on moderate-certainty evidence.
Low intake and deficiency are not the same thing, and the two are routinely conflated. ODS states symptomatic deficiency from low dietary intake is uncommon in healthy people because the kidneys limit urinary loss, while an analysis of NHANES 2013–2016 found 48% of Americans consume less magnesium from food than the Estimated Average Requirement. There is no current US population status data at all: serum magnesium has not been measured in NHANES since 1974. ODS also states there is no clear scientific evidence that vitamin and mineral supplementation benefits people with diabetes absent an underlying deficiency, and that magnesium only marginally lowers blood pressure.
Safety is established: supplemental excess above the 350 mg/day upper intake level causes diarrhoea, nausea and abdominal cramping, frank toxicity appears at far higher intakes and chiefly from laxatives and antacids, and the principal risk group is renal impairment. No hepatotoxicity signal.
At a glance
A cofactor for several hundred enzymatic reactions and the obligate counter-ion in the Mg-ATP complex; it modulates NMDA receptors and voltage-gated calcium channels and acts as a physiological calcium antagonist in vascular smooth muscle. The electrolyte and enzymatic roles are confirmed in humans — frank hypomagnesaemia produces arrhythmia, tetany and neuromuscular irritability, correctable by repletion. **The sleep and anxiety mechanisms are not confirmed in humans**: no high-quality meta-analysis demonstrating them was located, and the strongest Cochrane-level test of a neuromuscular claim was null.
Dated determinations, each flagged for whether it is final and whether it covers safety only. A safety review is not an efficacy finding, and most reporting in this category conflates the two.
No FDA warnings located. The same cation is simultaneously a supplement ingredient and an OTC drug active, which is why toxicity reports cluster around laxative and antacid use rather than supplement use.
NIH ODS fact sheet updated 6 January 2026. The limit protects against diarrhoea, nausea and abdominal cramping. Frank toxicity — hypotension, vomiting, difficulty breathing, irregular heartbeat, cardiac arrest, with earlier signs of nausea, facial flushing, urinary retention and lethargy — generally appears once serum magnesium exceeds 1.74–2.61 mmol/L, typically with intakes above about 5,000 mg/day from laxatives and antacids; fatal hypermagnesaemia has been reported in a child and an elderly man. The principal risk group is renal impairment, where excretion is limited.
In the Annex of authorised claims under Regulation (EU) 432/2012; each requires only that the food be at least a "source of" magnesium, with no daily amount specified. The authorised "normal muscle function" claim sits alongside moderate-certainty Cochrane evidence that cramp prophylaxis in older adults is unlikely to be clinically meaningful.
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