Magnesium is commonly used to prevent or treat leg cramps, especially in pregnancy and among older adults. The rationale stems from magnesium’s role in neuromuscular function and muscle relaxation. Some randomized controlled trials (RCTs) and systematic reviews have sought to clarify its effectiveness. A 2020 Cochrane review concluded that oral magnesium supplementation probably makes little or no difference in reducing the frequency or severity of leg cramps in the general population (including older adults), though the evidence was of moderate certainty. However, some studies in pregnant women suggest a modest reduction in cramp frequency, though findings are inconsistent and the quality of evidence is low to moderate.

Overall, while magnesium is used for muscle cramps based on its physiological role and traditional use, scientific evidence supporting its effectiveness is weak to moderate at best. The American Academy of Neurology and other clinical guidelines generally do not recommend magnesium for idiopathic leg cramps due to insufficient benefit demonstrated in clinical trials. Side effects (mainly gastrointestinal) are usually mild, but unnecessary supplementation is not advised unless magnesium deficiency is likely.

In summary, magnesium’s use for leg cramps is supported by some scientific investigation, but the overall evidence is limited and inconsistent. Its efficacy appears more likely in individuals who are actually magnesium deficient.