Background Lifetime prevalence of depression in subjects with opioid dependence is higher than in the general population (44-54% versus 16%) and represents a risk factor for morbidity and mortality. For patients on opioid agonist treatment, current prevalence rates of depression ranges between 10 and 30%, influencing negatively the outcome of the treatment. Objectives To evaluate the efficacy and the acceptability of antidepressants for the treatment of depressed opioid dependents treated with opioid agonists. Search strategy We searched Pubmed, EMBASE, CINAHL (to October 2009), CENTRAL (The Cochrane Library Cochrane Drug and Alcohol Group Specialised Register, issue 4, 2009), main electronic sources of ongoing trials, specific trial databases and reference lists of all relevant papers. Selection criteria Randomised and controlled clinical trials examining the efficacy of any antidepressant medication to treat depressed opioid dependents in treatment with opioid agonists. Data collection and analysis Two authors independently screened and extracted data from studies. Main results Seven studies, 482 participants, met the inclusion criteria. - Comparing antidepressant with placebo, no statistically significant results for dropouts. Selecting studies with low risk of bias, 325 participants, results favour placebo, RR1.40 (Cl 95% 1.00 to 1.96). For severity of depression, results from two studies, 183 participants, favour antidepressants utilising Clinical Global Impression Scale RR 1.92 (CI 95% 1.26 to 2.94), while another study, 95 participants,utilising the Hamilton Depression Rating Scale, did not find a statistically significant difference RR 0.96 (CI 95% 0.54 to 1.71). For adverse events, result favour placebo, four studies, 311 participants, RR 2.90 (Cl 95% 1.23 to 6.86). For drug use, three studies, 211 participants, it was not possible to pool data because outcomes' measures were not comparable. Looking at singular studies, no statistically significant difference was seen. - Comparing different classes of antidepressants, the results favour tricyclics for severity of depression, two studies, 183 participants, RR 1.92 (Cl 95% 1.26 to 2.94) and favour placebo for adverse events, two studies, 172 participants, RR 3.11 (Cl 95% 1.06 to 9.12). Authors' conclusions There is low evidence, at the present, supporting the clinical use of antidepressants for the treatment of depressed opioid addicts in treatment with opioid agonists. There is a need of larger randomised studies investigating relevant outcomes, safety issues and reporting data to allow comparison of results.