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Original Investigation
May 2017

Effect of Magnesium Oxide Supplementation on Nocturnal Leg CrampsA Randomized Clinical Trial

Author Affiliations
  • 1Clinical Research Unit, Clalit Health Services, Haifa and Western Galilee District, Israel
  • 2Department of Family Medicine, Technion–Israel Institute of Technology, Haifa, Israel
JAMA Intern Med. 2017;177(5):617-623. doi:10.1001/jamainternmed.2016.9261
Key Points

Question  Is magnesium oxide significantly more effective than placebo in reducing the frequency of nocturnal leg cramps?

Findings  In this randomized clinical trial that included 94 adults, the mean number of nocturnal leg cramps per week decreased significantly in both the magnesium oxide and placebo groups, with no significant difference between the groups.

Meaning  This trial suggests that magnesium oxide is not significantly better than placebo for alleviating nocturnal leg cramps.


Importance  Magnesium supplements are widely marketed for prophylaxis of nocturnal leg cramps (NLC) despite no evidence of significant benefit.

Objective  To determine whether magnesium oxide is better than placebo for NLC prophylaxis.

Design, Setting, and Participants  A randomized, double-blind, placebo-controlled clinical trial of 2 weeks eligibility screening followed by 4 weeks of treatment was conducted in northern Israel, from February to October 2013. An intention-to-treat data analysis was performed from March 22, 2014, to April 17, 2016. We used a volunteer sample of community-dwelling individuals experiencing NLC, 21 years or older, with 4 or more documented episodes of NLC during 2 weeks of screening.

Interventions  Capsules containing either magnesium oxide or a similar-looking placebo to be taken orally, once daily at bedtime for a period of 4 weeks.

Main Outcomes and Measures  The primary outcome was the difference in the mean number of NLC per week between the screening and treatment phases. Secondary outcomes included severity and duration of NLC, quality of life, and quality of sleep.

Results  Of the 166 volunteers, 72 (43%) were excluded, of whom 15 declined to participate and 57 did not meet the inclusion criteria. Of the 94 individuals (39% male; mean [SD] age, 64.9 [11.1] years) randomly assigned to magnesium oxide (48) or placebo (46), 6 did not complete the study protocol (3 in each group). Mean (SD) change of NLC was −3.41 (4.05) (from 7.84 [5.68] to 4.44 [5.66]) and −3.03 (4.53) (from 8.51 [5.20] to 5.48 [4.93]) per week in the magnesium oxide and placebo groups, respectively, a difference between groups of 0.38 (0.48) NLC per week (P = .67 in an intention-to-treat analysis). There were no between-group differences in the severity and duration of NLC, quality of life, or quality of sleep.

Conclusions and Relevance  Oral magnesium oxide was not superior to placebo for older adults experiencing NLC. The decrease in the mean number of NLC per week, from the screening to the treatment phase in both groups, is probably a placebo effect that may explain the wide use of magnesium for NLC.

Trial Registration  clinicaltrials.gov Identifier: NCT01709968