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Moderate evidenceSleep & relaxation

Magnesium

A mineral involved in over 300 enzymatic reactions. Supplementing makes a difference mainly for people with insufficient intake — which is common.

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What the science says

  • Better sleep in older adults with insomnia Moderate evidence

    A randomized controlled trial in older adults with insomnia showed improved sleep efficiency, sleep onset time, and melatonin levels with 500 mg/day. Evidence in young, healthy populations is weaker.

  • Blood pressure reduction Moderate evidence

    A meta-analysis of randomized trials showed a modest blood pressure reduction (~2 mmHg) with magnesium supplementation, with larger effects in people who are deficient.

  • Preventing muscle cramps Limited evidence

    A Cochrane review found no significant benefit of magnesium for cramps in adults in general.

Dosage & safety

Studied dose200–400 mg/day of elemental magnesium. Forms such as citrate, bisglycinate, and malate are better absorbed than oxide.
SafetyHigh doses have a laxative effect (mainly oxide and citrate). People with kidney impairment should not supplement without medical guidance.

How to take it

TimingEvening if you are taking it for sleep or cramps; otherwise timing does not matter.
With food?With food — it reduces the loose stools that are the most common reason people stop.
Worth knowingIf magnesium gives you diarrhoea, change the form (glycinate or malate) rather than cutting the dose — oxide and citrate are the laxative culprits.

Interactions

With medications

  • tetracycline and fluoroquinolone antibiotics

    Magnesium chelates these antibiotics in the gut and markedly reduces how much drug is absorbed. take the antibiotic at least 2 hours before or 4-6 hours after magnesium

  • levothyroxine

    Absorption of thyroid hormone is reduced. separate by at least 4 hours

  • bisphosphonates (alendronate, risedronate)

    Absorption is substantially reduced. separate by at least 2 hours, taking the bisphosphonate first on an empty stomach

  • potassium-sparing diuretics (spironolactone, amiloride)

    Magnesium retention increases, raising the risk of high blood magnesium, especially with reduced kidney function. do not supplement without medical guidance

With other supplements

  • high-dose zinc

    Zinc above roughly 140 mg/day reduces magnesium absorption and balance. take them at different times of day if you use high-dose zinc

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does magnesium help you sleep?

The evidence for magnesium and sleep is moderate and applies mainly to older adults with insomnia, where a randomized trial found 500 mg/day improved sleep efficiency and sleep onset. In young, healthy people the evidence for magnesium is weaker.

Which form of magnesium is best absorbed?

Magnesium citrate, bisglycinate and malate are absorbed better than magnesium oxide. If magnesium gives you diarrhoea, switch to glycinate or malate rather than cutting the dose.

How much magnesium per day?

The usual range is 200–400 mg/day of elemental magnesium, taken with food; take it in the evening if sleep is the goal. People with kidney impairment should not take magnesium without medical guidance.

Does magnesium work for muscle cramps?

Probably not — the evidence is limited. A Cochrane review found no significant benefit of magnesium for muscle cramps in adults in general.

Scientific references

Where to buy

NOW Foods, Magnesium Glycinate, 180 Tablets (100 mg per Tablet)

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