Frusso 1999.

Study characteristics
Methods	Double‐blind RCT of cross‐over design
Participants	45 non‐pregnant rest cramp sufferers > 18 years (mean age 61.6 years) having a normal neurologic exam and at least 6 leg cramps in a 4‐week placebo run‐in. Recruitment from a single large university‐based Argentinean family practice clinic
Interventions	Magnesium citrate 900 mg pill (approximately 100 mg elemental magnesium) (n = 45) twice daily or similar‐tasting and appearing placebo (n = 45), each for 4 weeks. 4‐week placebo run‐in and 4‐week washout between treatments
Outcomes	Primary: number of cramps in treatment period Secondary: Cramp duration by 4 ordinal categories (< 5 minutes; 5 to 10 minutes; 10 to 30 minutes; > 30 minutes) Cramp intensity by “analog scale” Sleep disturbance on a 0 to 10 scale with 0 = “no sleep disturbance” and 10 = “could not sleep because of the cramps” Adverse events
Conflicts of interest	No mention of conflicts of interest
Funding	Independent funding
Notes	Published. The 4‐week placebo run‐in was pre‐randomization. Unclear what the range for the analog scale of intensity is (assumed 0 to 10). Cramp duration was recorded by ordinal category but reported with a mean and standard deviation in minutes. Conducted from March 1996 to March 1997
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “Patients randomly received magnesium or placebo...” Comment: unclear how randomization was performed
Allocation concealment (selection bias)	Unclear risk	Quote: “The codes were inside a sealed envelope opened at the end of the analysis.” Comment: unclear who allocated participants and maintained the blinding
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: “Each pill contained 900 mg of magnesium citrate or matched placebo (same appearance and taste).” Comment: satisfactory blinding
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Outcomes measured via diaries completed by participants blind to the intervention
Incomplete outcome data (attrition bias) All outcomes	Low risk	3/45 participants withdrew with reasons given. Report does not state which intervention participants were receiving at the time or how their data were dealt with. Comment: probably satisfactory as the number of dropouts was small
Selective reporting (reporting bias)	Low risk	No indication of selective reporting for clinical endpoints (although urine for magnesium was collected and not reported). Duration of cramps was measured on a 4‐point ordinal scale but results were reported with the mean duration and standard deviation measured in minutes as though they were a continuous variable
Cramp diary (recall bias)	Low risk	Diary used
Other bias	Low risk	No obvious other bias