Recurrent Depressive Disorder

This is a randomised, placebo-controlled, parallel-group trial comparing OSU6162 at flexible dosage with placebo as add-on to treatment with an SSRI/SNRI in patients with depression that have not responded to treatment with an SSRI/SNRI per se for at least 6 weeks. The study will last for 6 weeks, after which those not having responded will leave the trial and those having responded will be offered to continue treatment without unblinding for another 4 weeks. Optional Substudy 1 and 2: Baseline and treatment-associated change in reward-related striatal activity per fMRI-assessment. (Substudy 1). Brain signal variability per fMRI-assessment. (Substudy 1). Probabilistic Reward Task (PRT). (Substudy 2). While assessment of the efficacy and safety of OSU6162 is the main objective of this study, possible differences between the two treatment groups with respect to a number of biomarkers in serum will also be explored. Multicenter trial: Multiple sites four Gothenburg, Lund, Stockholm and Uppsala.