Background: Seasonal affective disorder (SAD) is a seasonal pattern of recurrent major depressive episodes that most commonly occurs during autumn or winter and remits in spring. The prevalence of SAD ranges from 1.5% to 9%, depending on latitude. The predictable seasonal aspect of SAD provides a promising opportunity for prevention. This is one of four reviews on the efficacy and safety of interventions to prevent SAD; we focus on psychological therapies as preventive interventions.

Objectives: To assess the efficacy and safety of psychological therapies (in comparison with no treatment, other types of psychological therapy, second-generation antidepressants (SGAs), light therapy, melatonin or agomelatine or lifestyle interventions) in preventing SAD and improving patient-centred outcomes among adults with a history of SAD.

Search methods: We conducted a search of the Cochrane Depression, Anxiety and Neurosis Review Group Specialised Register (CCDANCTR) to 11 August 2015. The CCDANCTR contains reports of relevant randomised controlled trials from EMBASE (1974 to date), MEDLINE (1950 to date), PsycINFO (1967 to date) and the Cochrane Central Register of Controlled Trials (CENTRAL). Furthermore, we searched the Cumulative Index to Nursing and Allied Health Literature (CINAHL), Web of Knowledge, The Cochrane Library and the Allied and Complementary Medicine Database (AMED) (to 26 May 2014). We conducted a grey literature search (e.g. in clinical trial registries) and handsearched the reference lists of all included studies and pertinent review articles.

Selection criteria: To examine efficacy, we planned to include randomised controlled trials on adults with a history of winter-type SAD who were free of symptoms at the beginning of the study. To examine adverse events, we intended to include non-randomised studies. We planned to include studies that compared psychological therapy versus any other type of psychological therapy, placebo, light therapy, SGAs, melatonin, agomelatine or lifestyle changes. We also intended to compare psychological therapy in combination with any of the comparator interventions listed above versus the same comparator intervention as monotherapy.

Data collection and analysis: Two review authors screened abstracts and full-text publications against the inclusion criteria. Two review authors planned to independently extract data and assess risk of bias. We planned to pool data for meta-analysis when participant groups were similar and when studies assessed the same treatments versus the same comparator and provided similar definitions of outcome measures over a similar duration of treatment; however, we included no studies.

Main results: We identified 2986 citations through electronic searches and reviews of reference lists after de-duplication of search results. We excluded 2895 records during title and abstract review and assessed 91 articles at full-text review for eligibility. We found no controlled studies on use of psychological therapy to prevent SAD and improve patient-centred outcomes in adults with a history of SAD.

Authors' conclusions: Presently, there is no methodologically sound evidence available to indicate whether psychological therapy is or is not an effective intervention for prevention of SAD and improvement of patient-centred outcomes among adults with a history of SAD. Randomised controlled trials are needed to compare different types of psychological therapies and to compare psychological therapies versus placebo, light therapy, SGAs, melatonin, agomelatine or lifestyle changes for prevention of new depressive episodes in patients with a history of winter-type SAD.