Maule 1990.

Methods	RCT of cross‐over design
Participants	16 participants from general practice (mean age 76 years) who experienced at least 2 leg cramps per week
Interventions	2‐week washout then 4 blocks of 3‐week treatment periods consisting of quinine bisulphate (300 mg) or placebo or cork or wood in woollen bags
Outcomes	Cramp number, adverse events
Notes	Quinine compared against placebo and folklore. Only data provided is that for adverse events, but how many participants suffered these is not clear
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "were allocated to receive the three treatments and placebo in random order." Comment: details of randomisation not provided
Allocation concealment (selection bias)	Unclear risk	No mention of how allocation was concealed
Blinding (performance bias and detection bias) All outcomes	High risk	Quote: "the two tablets (quinine & placebo) should have been physically identical, but owing to lack of funds this criterion was not met." Comment: treatments were clearly distinguishable
Incomplete outcome data (attrition bias) All outcomes	High risk	There were 6 withdrawals from the trial; it is not clear from which treatment group they withdrew from, and the precise causes of the withdrawals are not given
Selective reporting (reporting bias)	Low risk	Quote: "During analysis of the data only average cramp number was considered because the duration section of the form was inadequately filled in by the majority of patients." Commment: suggests authors would have, as planned, analysed such data if they were available
Other bias	High risk	Treatments were sequential with no dedicated washout period between each phase, raising the possibility of significant carry‐over/withdrawal effects