Abstract: This review included five studies (with a total of 303 to 305 participants) comparing the effects of betahistine with placebo in adults with subjective idiopathic tinnitus. Four studies were parallel-group RCTs and one had a cross-over design. The risk of bias was unclear in all of the included studies. Due to heterogeneity in the outcomes measured and measurement methods used, very limited data pooling was possible. When we pooled the data from two studies for the primary outcome tinnitus loudness, the mean difference on a 0- to 10-point visual analogue scale at one-month follow-up was not significant between betahistine and placebo (-0.16, 95% confidence interval (CI) -1.01 to 0.70; 81 participants) (very low-quality evidence). There were no reports of upper gastrointestinal discomfort (significant adverse effect) in any study. As a secondary outcome, one study found no difference in the change in the Tinnitus Severity Index between betahistine and placebo (mean difference at 12 weeks 0.02, 95% CI -1.05 to 1.09; 50 participants) (moderate-quality evidence). None of the studies reported the other secondary outcomes of changes in depressive symptoms or depression, anxiety symptoms or generalised anxiety, or health-related quality of life as measured by a validated instrument, nor tinnitus intrusiveness. Other adverse effects that were reported were not treatment-related. There is an absence of evidence to suggest that betahistine has an effect on subjective idiopathic tinnitus when compared to placebo. The evidence suggests that betahistine is generally well tolerated with a similar risk of adverse effects to placebo treatments. The quality of evidence for the reported outcomes, using GRADE, ranged from moderate to very low. If future research into the effectiveness of betahistine in patients with tinnitus is felt to be warranted, it should use rigorous methodology. Randomisation and blinding should be of the highest quality, given the subjective nature of tinnitus and the strong likelihood of a placebo response. The CONSORT statement should be used in the design and reporting of future studies. We also recommend the development of validated, patient-centred outcome measures for research in the field of tinnitus.

Plain-language summary: Our review identified five randomised controlled trials with a total of 303 to 305 participants who suffered from tinnitus. These studies compared participants receiving betahistine to those receiving a placebo. Four study designs allocated participants into parallel groups. In one study, participants consented to take all study medications in a pre-defined sequence. The outcomes that we evaluated included tinnitus loudness and intrusiveness, tinnitus symptoms and side effects. The included studies did not show differences in tinnitus loudness, severity of tinnitus symptoms or side effects between participants receiving betahistine and participants receiving a placebo. No significant side effects were reported. We had planned to evaluate changes in tinnitus intrusiveness, depression and anxiety and quality of life, but these were not measured. The evidence suggests that betahistine is generally well tolerated with a similar risk of side effects to placebo. The quality of the evidence ranged from moderate to very low. The risk of bias in all of the included studies was unclear. The results were drawn from one or two studies only. In some studies, the participants that were included did not fully represent the entire population of people with tinnitus and so we cannot draw general conclusions.