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BACKGROUND: Nocturnal leg cramps are common and distressing. The only treatmentof proven effectiveness is quinine, but this has a number of side effects. Magnesium salts have beenshown to reduce leg cramp distress in pregnancy. This study tests whether magnesium citrate is effectivein the treatment of leg cramps in non-pregnant individuals by conducting in a randomised, double-blind,cross-over placebo-controlled trial. MATERIAL/METHODS: Volunteers suffering regular leg cramps were recruited.Magnesium citrate equivalent to 300 mg magnesium and matching placebo were given for 6 weeks each. Thenumber of cramps recorded in the cramp diary during the final 4 weeks of magnesium and placebo treatment,severity and duration of cramps and the participants' subjective assessment of effectiveness were analysed.RESULTS: In subjects who started with placebo (n=29) the median (95% CI) number of cramps was 9 (6-17)on placebo and 5 (4-8) on magnesium. For the group starting with magnesium (n=17) the median no of crampswas 9 (5-13) on magnesium and 8 (4-14) on placebo. There was no significant carry-over effect (p=0.88),but a highly significant period effect (p=0.008). There was a trend towards less cramps on magnesium(p=0.07). There was no difference in cramp severity and duration between the groups. Significantly moresubjects thought that the treatment had helped after magnesium than after placebo 36 (78%) and 25 (54%)respectively, (p=0.03). Diarrhoea was recorded as a side effect of magnesium. CONCLUSIONS: The resultssuggest that magnesium may be effective in treatment of nocturnal leg cramps. Further evaluation is recommended.