Depression and opiate-use disorders (abuse, dependence) often co-occur, each condition complicating the course and outcome of the other. It has been recommended that clinicians prescribe antidepressant therapy for mood symptoms in patients with active substance-use disorders, but whether antidepressants are effective in this specific population is not entirely clear. Therefore, the aim of this study was to examine the efficacy of antidepressants in patients with unipolar major depressive disorder (MDD) and/or dysthymic disorder (DD) with comorbid opiate-use disorders currently in methadone maintenance treatment (MMT). Medline/PubMed publication databases were searched for randomized, double-blind, placebo-controlled trials of antidepressants used as monotherapy for the treatment of MDD/DD in patients with comorbid opiate-use disorders currently in MMT. The search was limited to articles published between January 1, 1980, and June 30, 2010 (inclusive). Four manuscripts were found eligible for inclusion in our analysis (n = 317 patients). We found no statistically significant difference in response rates between antidepressant and placebo therapy in trials of MDD/DD patients with comorbid opiate-use disorders currently in MMT (risk ratio for response, 1.182; 95% CI: 0.822-1.700; P = 0.366). These results show no difference in the depressive outcome of patients with comorbid opiate-use disorders on MMT whether they are on medication or placebo. Future studies examining the effectiveness of antidepressants while controlling for several variables such as psychosocial treatment and assessing the specific classes of antidepressants are needed.