METHODS: This study was a systematic review and meta-analysis including articles published in the SID, MagIran, IranMedex, IranDoc, Cochrane, Embase, ScienceDirect, Scopus, PubMed and Web of Science databases were searched systematically to find articles published from 2006 to March 2019. Heterogeneity index was determined using the Cochran's test (Qc) and I2. Considering heterogeneity of studies, the random effects model was used to estimate the standardized difference of mean score for depression. Subsequently, the level of depression reduction in Iran and worldwide in the intervention group before and after the testwas measured.
RESULTS: A total of 19 articles met the inclusion criteria, and were therefore selected for this systematic review and meta-analysis. The sample size of the intervention group in the selected studies was 1948. According to the meta-analysis results, the mean depression score in the intervention group was 26.4 ± 5.6 and 18.4 ± 2.6 before and after intervention respectively, indicating the reducing effect of methadone on depression, and this difference was statistically significant (P