Underrepresentation of diverse populations and clinical characterization in opioid agonist treatment research: A systematic review of the neurocognitive effects of buprenorphine and methadone treatment.

ABSTRACT

INTRODUCTION: The relative neurocognitive effects of the two most common opioid agonist treatments (OAT; buprenorphine and methadone) for opioid use disorder (OUD) are poorly understood. The aim of this systematic review is to examine the neurocognitive effects of OAT (buprenorphine and methadone) and the clinical and sociodemographic characteristics of study samples. METHODS: The research team queried PubMed, PsycINFO and Cochrane Reviews for articles (01/1980-01/2020) with terms related to neurocognitive testing in adults (age ≥ 18) prescribed OAT. The team extracted neurocognitive data and grouped them by domain (e.g., executive functioning, learning/memory), and assessed study quality. RESULTS: The search retrieved 2341 abstracts, the team reviewed 278 full articles, and 32 met inclusion criteria. Of these, 31 were observational designs and one was an experimental design. Healthy controls performed better across neurocognitive domains than OAT-treated persons (buprenorphine or methadone). Compared to those with active OUD, OAT-treated persons had better neurocognition in various domains. However, in seven studies comparing buprenorphine- and methadone-treated persons, buprenorphine was associated with better neurocognition than was methadone, with moderate to large effect sizes in executive functioning, attention/working memory, and learning/memory. Additionally, OAT research underreports clinical characteristics and underrepresents Black and Latinx adults, as well as women. CONCLUSIONS: Findings suggest that compared to active opioid use, both buprenorphine and methadone treatment are associated with better neurocognitive functioning, but buprenorphine is associated with better executive functioning, attention/working memory, and learning/memory. These findings should be interpreted with caution given widespread methodological heterogeneity, and limited representation of ethnoracially diverse adults and women. Rigorous longitudinal comparisons with more diverse, better characterized samples will help to inform treatment and policy recommendations for persons with OUD.