Jansen 1997.

Methods	Double‐blind, parallel group RCT, set in the Netherlands
Participants	106 adult participants from general population who suffered at least 3 muscle cramps per week
Interventions	Hydroquinine hydrobromide dihydrate 300 mg daily (200 mg at supper, 100 mg at bedtime) or placebo for 2 weeks
Outcomes	Cramp number, cramp days, cramp intensity (graded 1 = mild to 10 = severe), cramp duration, cramp location, adverse events
Notes	Adult volunteers were recruited via a notice in a regional newspaper, and posters in pharmacies and libraries
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "An independent investigator used the random‐number generator of the SAS program to create the randomisation schedule."
Allocation concealment (selection bias)	Low risk	Quote: "All investigators involved in the study and all participants were unaware of the treatment allocation."
Blinding (performance bias and detection bias) All outcomes	High risk	Quote: "The only side‐effect definitely related to hydroquinine was a bitter taste or dry mouth (ten participants)..." Comment: inadequate blinding with high risk of bias
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants who failed to complete the trial were accounted for
Selective reporting (reporting bias)	Unclear risk	Data were collected with respect to cramp duration, severity and location, in addition to the primary outcome of frequency. However little actual data are presented to justify the "insignificant differences between drug and placebo" reported, and no mention of results for cramp location is made
Other bias	Unclear risk	Quote: "We recruited volunteers through notices in regional newspapers and posters in libraries and pharmacies."