"I's" on the prize: A systematic review of individual differences in Contingency Management treatment response.

Contingency Management is an evidence-based treatment for substance use disorders with strong potential for measurement-based customization. Previous work has examined individual difference factors in Contingency Management treatment response of potential relevance to treatment targeting and adaptive implementation; however, a systematic review of such factors has not yet been conducted. Here, we summarize and evaluate the existing literature on patient-level predictors, mediators, and moderators of Contingency Management treatment response in stimulant and/or opioid using outpatients - clinical populations most frequently targeted in Contingency Management research and clinical practice. Our search strategy identified 648 unique, peer-reviewed publications, of which 39 met full inclusion criteria for the current review. These publications considered a variety of individual difference factors, including (1) motivation to change and substance use before and during treatment (8/39 publications), (2) substance use comorbidity and chronicity (8/39 publications), (3) psychiatric comorbidity and severity (8/39 publications), (4) medical, legal, and sociodemographic considerations (15/39 publications), and (5) cognitive-behavioral variables (1/39 publications). Contingency Management was generally associated with improved treatment outcomes (e.g., longer periods of continuous abstinence, better retention), regardless of individual difference factors; however, specific patient-level characteristics were associated with either an enhanced (e.g., more previous treatment attempts, history of sexual abuse, diagnosis of antisocial personality disorder) or diminished (e.g., complex post-traumatic stress symptoms, pretreatment benzodiazepine use) response to Contingency Management. Overall, the current literature is limited but existing evidence generally supports greater benefits of Contingency Management in patients who would otherwise have a poorer prognosis in standard outpatient care. It was also identified that the majority of previous work represents a posteriori analysis of pre-existing clinical samples and has therefore rarely considered pre-specified, hypothesis-driven individual difference factors. We therefore additionally highlight patient-level factors that are currently understudied, as well as promising future directions for measurement-based treatment adaptations that may directly respond to patient traits and states to improve Contingency Management effectiveness across individuals and over time.