Effectiveness of single-session therapy for adult common mental disorders: a systematic review

Common mental disorders (CMDs) impose significant socioeconomic impacts on the global community. Nevertheless, over 50% of individuals with CMDs do not receive proper treatment, indicating that the current treatment modalities do not adequately tackle this issue. Since single-session therapy (SST) is a potential method for reducing the treatment gap, it is crucial to evaluate its effectiveness. Therefore, this systematic review aimed to evaluate the effectiveness of SST on CMD symptoms in adults.This systematic review included randomised and non-randomised studies assessing the clinical effectiveness of SST on CMD symptoms in adults. English-written, peer-reviewed studies or dissertations were included, while grey literature was excluded. MEDLINE, Embase, PsycINFO, and Cochrane's CENTRAL were searched on December 13, 2022, from their inception dates. The risk of bias in the included studies was evaluated using RoB 2 and ROBINS-I. A narrative synthesis was performed. This systematic review was registered in the PROSPERO database on July 6, 2022 (CRD42022343925).Six randomised and three non-randomised studies were included after screening 2,130 records. Three non-randomised studies with a "critical" or "serious" risk of bias were excluded from the synthesis. Therefore, six randomised trials involving 298 participants were included in the synthesis. Four out of six studies had a "high" risk of bias. The participants had non-severe symptoms at baseline, and three intervention types (behavioural activation, DBT, and solution-focused psychotherapy) were evaluated. Five of six studies showed positive results for depression, with only one reporting a positive result for anxiety.SST may be effective in improving CMD symptoms in adults, particularly depression. However, there is a limit to deriving definite conclusions due to a high risk of bias in included studies, insufficient sample size and research volume. Further research exploring the characteristics of clients who can benefit from SST is required to facilitate its widespread use.