Okamoto 1968.

Study characteristics
Methods	Allocation: random number allocation from a table by independent person not connected with the trial Design: parallel‐group
Participants	Number: 40 randomised Age: teens to 70s Gender: 13 M, 23 F Setting: specialist unit, Japan Eligibility criteria: Ménière's disease (clinically defined) Exclusion criteria: vertigo due to other causes, e.g. central disorders Baseline characteristics: similar pre‐trial symptom scores
Interventions	Betahistine 18 mg twice a day versus placebo over 2 weeks Intervention group: n = 18 Comparator group: n = 18 Use of additional interventions: none
Outcomes	Primary outcome: vertigo (3‐point ordinal scale) Secondary outcomes: none
Funding sources	Not stated
Declarations of interest	Not stated
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Random number allocation from a table by independent person not connected with the trial (James 2001)
Allocation concealment (selection bias)	Low risk	Independently allocated identical bottles (James 2001)
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Double‐blind, but no further information
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Double‐blind, but no further information
Incomplete outcome data (attrition bias) All outcomes	High risk	2 (out of 20 randomised) patients withdrew from each group, not due to adverse effects (James 2001) Participants lost to follow‐up: 4
Selective reporting (reporting bias)	Low risk	Appropriate outcomes reported
Other bias	Unclear risk	—