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Limited evidencePhysical performance

Leg Cramp Formulas

Magnesium and electrolyte blends sold for night cramps. The best available evidence says magnesium probably does not meaningfully help idiopathic cramps in older adults; results in pregnancy and with newer magnesium salts are mixed.

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What the science says

  • Idiopathic cramps in older adults Limited evidence

    The 2020 Cochrane review of 11 RCTs (735 participants) concluded that magnesium is unlikely to provide a clinically meaningful reduction in cramp frequency in older adults with idiopathic cramps.

  • Pregnancy-related leg cramps Limited evidence

    A meta-analysis of randomized trials in pregnancy reported reduced cramp frequency with oral magnesium, but the trials were small and heterogeneous, and Cochrane rated the same body of evidence conflicting.

  • One positive trial with a specific magnesium salt Moderate evidence

    A double-blind, placebo-controlled multicentre trial of magnesium oxide monohydrate (226 mg once daily for 60 days, 175 completers) found a greater reduction in nocturnal cramp episodes than placebo. The result has not been replicated.

Dosage & safety

Studied doseTrials used roughly 200–450 mg/day of elemental magnesium at bedtime. Blends often add potassium, calcium or B vitamins, none of which has cramp-specific trial support.
SafetyMagnesium commonly causes loose stools, oxide most of all. It can accumulate dangerously in kidney impairment. Potassium-containing blends interact with ACE inhibitors, ARBs and potassium-sparing diuretics. Cramps that are new, severe or one-sided deserve a medical look.

How to take it

TimingAt bedtime, which is what the nocturnal-cramp trials used.
With food?With food, to soften the laxative effect.
Worth knowingChoose glycinate or citrate over oxide — oxide is poorly absorbed and is the form that empties your bowels.

Interactions

With medications

  • tetracycline and quinolone antibiotics

    Magnesium chelates the antibiotic in the gut and cuts absorption substantially. separate by at least 2 hours either side

  • levothyroxine

    Magnesium binds thyroid hormone and lowers the absorbed dose. separate by at least 4 hours

  • bisphosphonates

    Absorption of the bisphosphonate is markedly reduced. separate by at least 2 hours

  • ACE inhibitors, ARBs and potassium-sparing diuretics

    Potassium-containing blends add to the potassium these drugs already retain, risking hyperkalaemia. check the label for potassium and ask your doctor

With other supplements

  • other magnesium sources, including antacids and laxatives

    Total magnesium adds up fast and diarrhoea follows. count all sources together

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 night leg cramps?

Magnesium in leg cramp formulas has limited evidence: a 2020 Cochrane review of 11 RCTs (735 participants) concluded it is unlikely to meaningfully reduce cramp frequency in older adults with idiopathic cramps. One trial of magnesium oxide monohydrate at 226 mg once daily was positive but has not been replicated.

Does magnesium help leg cramps in pregnancy?

A meta-analysis of small, heterogeneous trials reported fewer pregnancy leg cramps with oral magnesium, but Cochrane rated the same evidence conflicting. The evidence for magnesium-based leg cramp formulas in pregnancy is limited.

How much magnesium should I take for leg cramps?

Cramp trials used roughly 200–450 mg/day of elemental magnesium at bedtime, taken with food to soften the laxative effect. The potassium, calcium or B vitamins added to leg cramp formulas have no cramp-specific trial support.

Can leg cramp formulas interact with medications?

The magnesium in leg cramp formulas reduces absorption of tetracycline and quinolone antibiotics and bisphosphonates (separate by at least 2 hours) and levothyroxine (at least 4 hours). Potassium-containing blends can cause hyperkalaemia with ACE inhibitors, ARBs and potassium-sparing diuretics.

Scientific references

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