Objectives: To describe the effectiveness of medications for the treatment of opioid use disorder (OUD) and attention deficit/hyperactivity disorder (ADHD). Data Sources: Literature search of PubMed, Embase, Web of Science, CINAHL, Medline, PsycINFO, and Google Scholar was performed for studies published from inception to October 25, 2022. Study Selection and Data Extraction: Studies were included if patients were diagnosed with OUD and ADHD and had pharmacotherapy for either condition. Abstracts, commentaries, reviews, case reports, case series, non-English articles, and animal studies were omitted. Data Synthesis: This review found 18 studies. Treatment of ADHD was evaluated for impact on ADHD and OUD outcomes, while treatment of OUD was evaluated for OUD-related outcomes. Outcomes assessed included markers for symptom intensity, adherence, and treatment failure. While results were mixed, treatment of ADHD was largely associated with improvements in ADHD severity and retention in OUD treatment programs. ADHD severity was associated with higher rates of illicit substance abuse and worse OUD-related outcomes. It could not be determined which medications for treatment of OUD should be prioritized. Relevance to Patient Care and Clinical Practice: This review summarized key findings from studies that treated ADHD or OUD among dually diagnosed patients and highlighted methodological considerations for future research. Conclusions: Treatment of ADHD is warranted among patients with OUD and ADHD to improve retention in OUD treatment programs and reduce illicit substance abuse. Pharmacotherapy for the treatment of ADHD or OUD should continue to be determined based on patients' characteristics and the capabilities of the treatment program.