The heterogeneity of depression suggests that 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 an endophenotype within the depression spectrum, with a distinct pathophysiology of 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. In this proof-of-concept pilot study the investigators test the anti-anhedonic and antidepressant effects of add-on pramipexole using an "enriched population study design" including only depressed patients with significant anhedonia. To understand the neurobiology of anhedonia in depression and to identify treatment predictors, the investigators also do assessments of anhedonia-related neurocircuitry using (f)MRI and blood biomarkers.

Inclusion Criteria:

1. Age ≥18 and ≤75.
2. Diagnosis of unipolar depression; bipolar disorder in depressive phase or dysthymia.
3. Symptoms of depression; Total-score ≥ 18, measured by Montgomery-Åsberg Depression Rating Scale (MADRS).
4. Symptoms of anhedonia; Total-score < 27, measured by Dimensional Anhedonia Rating Scale (DARS).
5. Ongoing treatment with at least one antidepressant drug ≥ 4 weeks without major changes in dosage. Patients with bipolar disorder must have a mood-stabilizing drug treatment.
6. Must sign an informed consent. -

Exclusion Criteria:

1. Ongoing pregnancy, breastfeeding or planning for pregnancy.
2. High suicidality assessed by the researcher with medical degree.
3. Ongoing substance use disorder (last 12 month).
4. Diagnosis of psychosis.
5. Ongoing involuntary psychiatric treatment.
6. History of Impulse-control disorder or current ADHD diagnosis.
7. Diagnosis of Intellectual disability, dementia, or other circumstances leading to difficulties to understand the implications of participating in the study and to give informed consent.
8. Diagnosis of renal failure (eGFR < 50 ml/min/1,73 m2 ) or severe cardiovascular disease (defined as symptoms of heart failure NYHA class 2).
9. Recently committed to psychotherapy (during the last 6 weeks) or planning for psychotherapy during the participation of the study.
10. Ongoing ECT-treatment.
11. Other diseases, disorders or medical treatments that according to the researchers might influence the results of the study or increases the risks of the study. Such as Parkinson's disorder, liver failure, cancer not in remission (for at least over a year).
12. Confirmed or suspected allergy to the active substance or excipients of the drug used in this study.
13. Committed to other trials
14. Other reasons that according to the researcher might prevent the subject to fulfill the obligations of the study. For example insufficient drug compliance. -

Open-label, only one arm

For each participant, adverse event data was collected for 14 weeks: every week for 10 weeks and an additional check-up at week 14.

According to EU regulation 536/2014 (Clinical Trials Regulation, CTR).

Inherent limitations and caveats of this test-of-feasibility study: small-scale (small sample) and open-label design.