Abstract: Seven studies were included in the analysis (368 participants in total). All were on mania, hypomania, mixed episodes or rapid-cycling disorder. Overall, their methodological quality was relatively low. There was no difference in the primary outcome analysis – a fall of  50% or more on the Young Mania Rating Scale (YMRS) - between oxcarbazepine and placebo (N=1, n=110, OR =2.10, 95% CI 0.94 to 4.73) in one study, conducted in children; no studies were available in adult participants. In comparison with other mood stabilisers, there was no difference between oxcarbazepine and valproate as an antimanic agent using the primary outcome (50% or more fall in YMRS, OR=0.44, 95% CI 0.10 to 1.97, 1 study, n=60, P=0.273) or the secondary outcome measure (differences in YMRS between the two groups, SMD=0.18, 95% CI -0.24 to 0.59, 2 studies, n=90, P=0.40). No primary or secondary efficacy outcome measures were found comparing oxcarbazepine with lithium monotherapy. As an adjunctive treatment to lithium, oxcarbazepine reduced depression rating scale scores more than carbamazepine in a group of manic participants on the Montgomery-Åsberg Depression Rating Scale (MADRS) (SMD=- 1.12, 95% CI -1.71 to -0.53, 1 study, n=52, P=0.0002) and on the Hamilton Depression Rating Scale (HDRS) (SMD=- 0.77, 95% CI -1.35 to -0.20, 1 study, n=52, P=0.008). There was a higher incidence of adverse effects, particularly neuropsychiatric, in participants randomised to oxcarbazepine compared to those on placebo (1 study, n=115, 17% to 39% of participants on oxcarbazepine had at least one such event compared to 7% to 10% on placebo).There was no difference in adverse events rates between oxcarbazepine and other mood stabilisers or haloperidol. Currently, there are insufficient trials of adequate methodological quality on oxcarbazepine in the acute treatment of bipolar disorder to inform us on its efficacy and acceptability. Studies predominantly examine the treatment of mania: there are data from subgroup analysis on mixed affective, hypomania and rapid-cycling states. From the few studies included in this review, oxcarbazepine did not differ in efficacy compared to placebo in children and adolescents. It did not differ from other active agents in adults. It may have a poorer tolerability profile compared to placebo. No data were found on outcomes relevant to patients and clinicians, such as length of hospital admission. There is a need for adequately powered randomised controlled trials of good methodological quality to inform us of the therapeutic potential of oxcarbazepine across the spectrum of acute episodes in bipolar disorder.

Plain-language summary: In this review we found seven studies that were eligible for inclusion, of which four studies compared the efficacy of oxcarbazepine to placebo or to other medications used in treating mania. While there was no evidence that oxcarbazepine worked better compared to a placebo, it did have similar efficacy to more accepted medications for the treatment of the illness. Two studies examined its acceptability to participants. Oxcarbazepine may cause more side effects than placebo. No differences in side effects were found between oxcarbazepine and other active medications. All the studies examined mania, hypomania, mixed episodes or rapid-cycling disorder. More studies of better methodological quality are needed if we are to be certain whether oxcarbazepine works or not when treating mania, mixed episodes, depression and rapid-cycling in bipolar disorder.