Summary of findings 2. Betahistine versus placebo (with concurrent medication).

Betahistine compared with placebo for tinnitus (with concurrent medication)
Patient or population: patients with subjective idiopathic tinnitus Settings: departments of otorhinolaryngology in hospitals worldwide Intervention: betahistine Comparison: placebo (vitamin B6)
Outcomes	Treatment effects		Relative effect (95% CI)	No of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Placebo (vitamin B6)	Betahistine
Change in tinnitus loudness match (range 0 to 5) Follow‐up: 1 week	The mean tinnitus loudness match was 2.5 in the control group	The mean tinnitus loudness match in the intervention group was 0.1 lower	‐0.10 (‐0.50 to 0.30)	60 (1)	⊕⊕⊕⊝ moderate1
Significant adverse effects (yes or no) Follow‐up: 1 week	Study population		RR 3.10 (0.13 to 73.14)	59 (1)	⊕⊕⊝⊝ low2
	34 per 1000	0 per 1000
Tinnitus symptom severity	Not measured
Depressive symptoms	Not measured
Symptoms of generalised anxiety	Not measured
Other adverse effects (yes or no) Follow‐up: 1 week	Study population		RR 0.44 (0.13 to 1.55)	59 (1)	⊕⊕⊕⊝ moderate1
	103 per 1000	233 per 1000
CI: confidence interval; RR: risk ratio
GRADE Working Group grades of evidence High‐quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate‐quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low‐quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low‐quality: We are very uncertain about the estimate.

¹Downgraded one level due to an unclear overall risk of bias.

²Downgraded one level due to an unclear overall risk of bias; downgraded one level due to imprecision.