Duphar H10803592F 1997.

Study characteristics
Methods	Allocation: randomised in groups of 4 using tables before study started Design: prospective, parallel, multicentre
Participants	Number: 144 Age: 18 to 70 Gender: not specified but groups statistically equal Setting: French ENT specialist units Eligibility criteria: recurrent vertigo (at least 2 attacks, at least 1 in last month) including Ménière's disease and other Exclusion criteria: medical and psychiatric disorders (specified), vertigo due to other causes, contraindication to betahistine Baseline characteristics: Table 2 shows statistical assessment of similarity
Interventions	Betahistine 24 mg twice a day versus placebo for 30 days Intervention group: n = 119 Comparator group: n = 116 Use of additional interventions: none
Outcomes	Primary outcome: frequency, severity, duration of attacks Secondary outcomes: patient and investigator global assessment
Funding sources	Unpublished manufacturer study
Declarations of interest	Unpublished manufacturer study
Notes	Unpublished trial
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomised in groups of 4 before study started using tables
Allocation concealment (selection bias)	Unclear risk	Sealed envelopes; opacity not stated
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"neither patient nor investigator knew which treatment was being given"
Blinding of outcome assessment (detection bias) All outcomes	Low risk	As above
Incomplete outcome data (attrition bias) All outcomes	High risk	Participants lost to follow‐up: 36. Reasons given for 28 of these.
Selective reporting (reporting bias)	Low risk	Outcomes clearly reported
Other bias	Unclear risk	Previous trial with betahistine excluded