Introduction
OUD
DISORDER, SECONDARY, ABUSE
Concomitant use of opioids and stimulants, primarily methamphetamine and cocaine, increased by over 80% in the past decade [However, concomitant stimulant use may reduce rates of MOUD initiation [Randomized clinical trials (RCTs) typically collect extensive covariate data that investigators can use to better control bias (i.e., increase internal validity) when investigating nonrandomized secondary questions. However, RCT samples are usually not representative of the larger populations intended to receive treatments under study [Transportability analysis is a novel analytic solution to this problem, formally defining when and how statistical estimates may be extrapolated from a given source population to a different target population [The primary aim of this study is to estimate the association between stimulant use and initiation of buprenorphine or XR-NTX for the treatment of OUD. To complete this aim, we conducted a two-part analysis. First, we estimated associations in pooled data of two NIDA-CTN clinical trials. Second, we generalized results to three target populations of interest: (1) civilian, noninstitutionalized, housed adults identifying the need for OUD treatment, as characterized by the National Survey on Drug Use and Health (NSDUH); (2) adults entering OUD treatment, as characterized by Treatment Episodes Dataset (TEDS); and (3) adults with opioid misuse and high rates of injection drug use (IDU) living in rural regions of the U.S., as characterized by the Rural Opioids Initiative cohort (ROI). Figure 
Study overview. Data from the source population, two National Drug Abuse Treatment Clinical Trials Network studies, is pooled to estimate the association between stimulant use and initiation of medication for opioid use disorder in the trials. Differences between trial participants and target populations are used to estimate the probability of trial participation. Inference is made in target populations by re-weighting trial participants to better match the characteristics of individuals in target populations