OBJECTIVE: To assess the antidepressant efficacy and tolerability of adjunctive pramipexole, a D2-D3 dopamine agonist, in patients with drug-resistant depression. METHODS: The study sample consisted of in-patients with major depressive episode, according to the DSM-IV, and drug resistance. Pramipexole was added to antidepressant treatment with TCA or SSRI, at increasing doses from 0.375 to 1.0 mg/day. Two independent response criteria were adopted: a > 50% reduction of the Montgomery-Asberg Depressive Rating Scale (MADRS) total score and a score of I or 2 on the Clinical Global Impression scale (CGI-1) at endpoint. Side-effects were assessed by the Dosage Record Treatment Emergent Symptom Scale (DOTES). RESULTS: Thirty-seven patients were enrolled. Of these. 16 had unipolar depression and 21 had bipolar depression. Six patients dropped out in the first week. Of the 31 patients included in the analyses. 19 completed the 16-week follow-up. Mean maximal dose of pramipexole was 0.95 mg/day. Mean scores on MADRS decreased from 33.3 +/- 8.4 at baseline to 13.9 +/- 11.5 at endpoint (p < 0.001) and the CGI-S decreased from 4.6 +/- 0.8 at baseline to 2.8 +/- 1.3 at endpoint (p < 0.001). At endpoint, 67.7% (21/31) of patients were responders on MADRS and 74.2% on CGI-I. Of the 37 patients enrolled, 10 discontinued pramipexole because of adverse events. CONCLUSIONS: These preliminary data suggest that pramipexole adjunction to antidepressant treatment may be effective and well tolerated in patients with resistant major depression.