The heterogeneity of depression suggests that several different neurocircuits and pathophysiological mechanisms are involved. Anhedonia - the inability to experience pleasure from, or the lack of motivation to carry out, usually enjoyable activities - is a promising endophenotype within the depression spectrum, with a distinct pathophysiology involving dopaminergic mesolimbic projections. Anhedonia is common in depression and associated with treatment resistance. Pramipexole, an agonist to the dopamine -receptor 3, is an established treatment of Parkinson's disease. Based on its mechanism of action, pramipexole might be efficacious in a subtype of depression characterized by anhedonia and lack of motivation - symptoms linked to dopaminergic hypofunction.~The aim of this open label follow-up study is to test the long-term efficacy and tolerability of add-on pramipexole in anhedonic depression. This is a continuation study of an RCT (EudraCT# 2022-001563-26) in which patients are randomized to either pramipexole or placebo for 9 weeks. After completion of the RCT, patients will be offered to participate in the current trial. Approximately 50% of the patients have been treated with pramipexole and 50% with placebo within the frames of the RCT. Patients randomized to pramipexole in the RCT will continue on their current dose and patients randomized to placebo will start pramipexole using the same dosing schedule as in the RCT. A total of 80 research subjects with unipolar depression, bipolar disorder in depressive phase, or dysthymia will be offered participation in the study after completing the RCT given that they fulfill all the inclusion criteria, and none of the exclusion criteria.~Subjects have study visits once a month during 6 months, or more often if needed based on side effects. Symptom severity, side effects and ecological momentary assessments are recorded at each study visit and dose titration schedule is modified as needed. Between study visits, research subjects may contact study personnel and the investigators can quickly arrange for an additional study visit if needed.~After the study, the decision to continue with pramipexole outside of the study or discontinue with pramipexole will be based on patient preference in combination with a willingness of the patient's regular physician to take over the treatment outside of the study.
The purpose of the study is to assess the long-term efficacy and safety of add-on pramipexole for treatment of patients with anhedonic depression.