Magnesium for skeletal muscle cramps.

Systematic review and meta-analysis of randomized trials in people with skeletal muscle cramps. Most evidence came from older adults with idiopathic nocturnal/rest cramps, with additional trials in pregnancy-associated leg cramps and one small trial in liver cirrhosis-associated cramps; no randomized trials were identified for exercise-associated cramps.

Magnesium supplementation was evaluated in multiple formulations and routes, most commonly oral magnesium lactate, magnesium oxide, magnesium aspartate, magnesium bisglycinate, or magnesium chewable tablets, with doses ranging from 122 mg to 520 mg elemental magnesium per day in most trials. One older-adult study used intravenous magnesium sulfate, and treatment durations were typically 4 to 12 weeks, compared with placebo or no treatment.

Magnesium is unlikely to provide clinically meaningful prophylaxis for skeletal muscle cramps in older adults, although pregnancy-associated cramps remain uncertain because the evidence is conflicting. In idiopathic rest cramps, pooled cramp frequency change at 4 weeks was not significant (MD -9.59%, 95% CI -23.14 to 3.97; 177 participants; 3 studies), and pooled cramp intensity was also essentially null (MD -0.02; 269 participants; 4 studies). At 12 weeks, the available older-adult data still did not show a clear benefit for cramp frequency (MD -12.09%, 95% CI -40.22 to 16.04; 43 participants) or intensity (MD -0.18; 43 participants). Minor adverse events were not clearly different from placebo overall (RR 1.51, 95% CI 0.98 to 2.33; 254 participants; 4 studies). One pregnancy trial reported more 50% cramp reduction with magnesium than placebo (79.0% vs 32.4%, P=0.003), but other pregnancy studies were inconsistent and poorly aligned for pooling.

The evidence base was small, heterogeneous, and often poorly reported, with differing magnesium salts, doses, routes, and outcome measures across trials. Several studies were underpowered, some pregnancy trials were open-label or had unusable data for pooling, and the cirrhosis trial was sparse and inconclusive. Generalizability is limited because most data came from older adults with idiopathic cramps, with little evidence for other cramp types.