Objective: Depression is the most common psychiatric comorbidity among people with opioid use disorders (OUDs). However, whether and how comorbid depression is associated with the outcomes of opioid agonist therapy (OAT) remains poorly understood. The objective of this review was to identify and describe the association between depression and main outcomes (opioid use and treatment retention) of methadone and buprenorphine treatment among people with OUDs. Methods: A literature review was conducted by searching five electronic databases (MEDLINE, PubMed, Embase, Evidence-Based Medicine Reviews [EBMR], and Cumulative Index of Nursing and Allied Health Literature [CINAHL] Complete) from January 1970 to April 2019. Two independent reviewers screened titles and abstracts of the identified records by using pre-established eligibility criteria. Next, full texts were reviewed and studies that met inclusion criteria were selected. Finally, a descriptive synthesis of extracted data was performed. Results: In total, 12,296 records were identified and 18 studies that met inclusion criteria were retained. Of these, six studies reported reduced opioid use and seven reported increased opioid use during methadone or buprenorphine treatment. In addition, three studies reported an increased retention rate and four documented a decreased retention rate during methadone or buprenorphine treatment. The remaining studies did not find any significant association between depression and opioid use or treatment retention. Overall, the evidence did not demonstrate a consistent association between depression and outcomes of methadone or buprenorphine treatment. Conclusions: Although the inconsistent nature of the current evidence prohibited us from drawing definitive conclusions, we posit that the presence of depression among OUDs patients may not always predict negative outcomes related to retention and drug use during the course of OAT. Particularly, the hypothesis that adequate treatment of depression can improve treatment retention is promising and is in line with the call for increased efforts to provide integrated care for comorbid mental health disorders and addiction. Future studies with rigorous methodology are essential to better characterize the complex interplay between depression, OAT, and OUDs.
Keywords: Depression; abstinence; opioid agonist therapy; opioid use disorder; retention.