Abstract: We included 17 studies, with a total of 1025 participants; 12 studies were published (567 patients) and five were unpublished (458 patients). Sixteen studies including 953 people compared betahistine with placebo. All studies with analysable data lasted three months or less. The majority were at high risk of bias, but in some the risk of bias was unclear. One study, at high risk of bias, included 72 people with benign paroxysmal positional vertigo (BPPV) and compared betahistine with placebo; all patients also had particle repositioning manoeuvres. The studies varied considerably in terms of types of participants, their diagnoses, the dose of betahistine and the length of time it was taken for, the study methods and the way any improvement in vertigo symptoms was measured. Using the GRADE system, we judged the quality of evidence overall to be low for two outcomes (proportion of patients with improvement and proportion with adverse events). Pooled data showed that the proportion of patients reporting an overall reduction in their vertigo symptoms was higher in the group treated with betahistine than the placebo group: risk ratio (RR) 1.30, 95% confidence interval (CI) 1.05 to 1.60; 606 participants; 11 studies). This result should be interpreted with caution as the test for statistical heterogeneity as measured by the I2 value was high. Adverse effects (mostly gastrointestinal symptoms and headache) were common but medically serious events in the study were rare and isolated: there was no difference in the frequency of adverse effects between the betahistine and placebo groups, where the rates were 16% and 15% respectively (weighted values, RR 1.03, 95% CI 0.76 to 1.40; 819 participants; 12 studies). Sixteen per cent of patients from both the betahistine and the placebo groups withdrew (dropped out) from the studies (RR 0.96, 95% CI 0.65 to 1.42; 481 participants; eight studies). Three studies looked at objective vestibular function tests as an outcome; the numbers of participants were small, techniques of measurement very diverse and reporting details sparse, so analysis of this outcome was inconclusive. We looked for information on generic quality of life and falls, but none of the studies reported on these outcomes. Low quality evidence suggests that in patients suffering from vertigo from different causes there may be a positive effect of betahistine in terms of reduction in vertigo symptoms. Betahistine is generally well tolerated with a low risk of adverse events. Future research into the management of vertigo symptoms needs to use more rigorous methodology and include outcomes that matter to patients and their families.

Plain-language summary: We included 17 studies, with a total of 1025 participants. Sixteen studies including 953 people compared betahistine with placebo; the studies were at high to unclear risk of bias. All studies with analysable data lasted three months or less. One study, at high risk of bias, included 72 people with benign paroxysmal positional vertigo (BPPV) and compared betahistine with placebo; all patients also had particle repositioning manoeuvres. We judged the quality of evidence overall to be low. The studies varied considerably in terms of types of participants, their diagnoses, the dose of betahistine and the length of time the drug was taken for, the study methods and the way any improvement in vertigo symptoms was measured. When all studies are taken together, the proportion of patients reporting a reduction of their vertigo symptoms was significantly higher in the betahistine group than in the placebo group. However, there was significant variability in the results of the studies so this result should be treated with caution. The proportion of patients reporting side effects of the medication was similar in both groups: 16% in the betahistine groups and 15% in the placebo groups. Overall, 16% of patients of both groups withdrew from the studies. There was insufficient information about the effect of betahistine on objective tests of inner ear balance organ function. There was no information on the effect of betahistine on overall quality of life or falls. We judged the quality of evidence from the included studies to be low, meaning our estimates of the effects of betahistine could turn out to be inaccurate. The evidence is up to date to September 2015. Low quality evidence suggests that patients suffering from vertigo from different causes may have some benefit from betahistine in terms of reduction in vertigo symptoms. Betahistine is generally well tolerated. Future research into the management of vertigo symptoms needs to use more rigorous methodology and include outcomes that matter to patients and their families.