Does Magnesium Supplementation Treat Nocturnal Leg Cramps?

Is magnesium supplementation an effective treatment for nocturnal leg cramps?

Probably not. Magnesium supplementation should not be used for short courses (less than 60 days) to treat idiopathic or pregnancy-related nocturnal leg cramps. (Strength of Recommendation [SOR]: B, systematic reviews of randomized controlled trials [RCTs], highly heterogeneous studies.) There is limited evidence that magnesium oxide may improve nocturnal leg cramps after 60 days of treatment. (SOR: B, single RCT.)

A 2020 systematic review of 11 RCTs (open-label, single-blind, or double-blind with nine parallel groups and two crossover studies; n = 735) evaluated the effectiveness of magnesium supplementation in patients of any age to prevent skeletal muscle cramps associated with pregnancy, cirrhosis, or unknown etiology.¹ The review found no reduction in leg cramps. Five trials enrolled women with pregnancy-associated leg cramps (n = 408), five trials enrolled participants with idiopathic cramps (n = 271), and one trial enrolled 29 participants with cirrhosis who reported having cramps. Most trials provided magnesium as an oral supplement in different dosing frequencies: once (three trials), twice (five trials), or three times (two trials) daily. One study provided magnesium as a five-day series of four-hour slow intravenous infusions. Nine trials compared magnesium with placebo; one trial compared magnesium with no treatment, calcium carbonate, or vitamin B; and one trial compared magnesium with vitamin E or calcium.

For idiopathic leg cramps, the mean percentage change from baseline in the number of cramps per week at four weeks was not notable between magnesium and placebo (three studies; n = 177; mean difference [MD] = −9.59%; 95% CI, −23.14% to 3.97%; moderate-certainty evidence).1 There was no difference in the number of leg cramps per week at four weeks (five studies; n = 307; MD = −0.18 cramps per week; 95% CI, −0.84 to 0.49; moderate-certainty evidence). No significant differences were found between treatment and placebo for any secondary outcomes. These included at least a 25% reduction in the rate of leg cramps from baseline (three studies; n = 177; risk ratio [RR] = 1.04; 95% CI, 0.84 to 1.29; high-certainty evidence), the number of participants rating their leg cramps as moderate to severe at four weeks (two studies; n = 91; RR = 1.33; 95% CI, 0.81 to 2.21; moderate-certainty evidence), the percentage reduction in leg cramps at 12 weeks (one study; MD = −12.09%; 95% CI, −40.22% to 16.04%; n = 43), and achieving at least a 25% reduction in the frequency of leg cramps at 12 weeks (one study; n = 43; RR = 1.22; 95% CI, 0.70 to 2.1).

In patients with pregnancy-associated leg cramps (mean age = 29.3 years), the data had high heterogeneity (only one participant used a cramp diary), which prevented pooling of the data.¹ All five trials were judged to be at high risk of bias. One study comparing magnesium with no treatment found no benefit on overall effectiveness. Of the three trials comparing magnesium to placebo, one found no benefit for frequency or intensity, another found benefit for both, and the last trial reported inconsistent and irreconcilable results for frequency. No statistically significant differences were noted in minor adverse effects between the treatment and placebo groups (four studies; n = 254; RR = 1.51; 95% CI, 0.98 to 2.33; low-certainty evidence). Oral magnesium supplementation was associated with mostly gastrointestinal adverse effects (e.g., diarrhea), experienced by 11% to 37% of the magnesium group compared with 10% to 14% of the control group.