Marks C, Borquez A, Jain S, et al. - In the present study, the researchers evaluated the connection between recent opioid agonist treatment (OAT) enrollment and assisting injection drug use (IDU) initiation across several North American settings and employed dynamic modeling to project the potential population-level impact of OAT scale-up within the person who injects drugs (PWID) population on IDU initiation. A prospective multicohort study of PWID in 3 settings (Vancouver, Canada [n = 1,737]; San Diego, United States [n = 346]; and Tijuana, Mexico [n = 532]) from 2014 to 2017 was used to obtain data for this researchers. Findings suggested an association of past–6-month enrollment in OAT with almost half the likelihood of past–6-month provision of assistance with IDU initiation. A dynamic model of IDU initiation was parameterized using these associations, and the population-level influence of scaling up OAT coverage on IDU initiations over the next decade was estimated in a generic North American setting. It was estimated that scaling up of OAT coverage from approximately 21% to 60% among PWID can reduce the number of people who initiate IDU each year by 23% after a decade. Such findings suggested that improving OAT coverage among PWID can have an important influence on reducing IDU initiations in addition to its known advantages of preventing HIV, hepatitis C virus, and overdose among PWID.