ABSTRACT. Objective: Medications for the treatment of substance use disorders (SUDs) are not widely available in publicly funded SUD treatment programs. Few studies have drawn on longitudinal data to examine the organizational characteristics associated with programs transitioning from not delivering any pharmacotherapy to adopting at least one SUD medication. Method: Using two waves of panel longitudinal data collected over a 5-year period, we measured the transition to medication adoption in a cohort of 190 publicly funded treatment organizations that offered no SUD medications at baseline. Independent variables included organizational characteristics, medical resources, funding, treatment culture, and detailing activities by pharmaceutical companies. Results: Of 190 programs not offering SUD pharmacotherapy at baseline, 22.6% transitioned to offering at least one SUD medication at follow-up approximately 5 years later. Multivariate logistic regression results indicated that the employment of at least one physician at baseline, having a greater proportion of Medicaid clients, and pharmaceutical detailing were positively associated with medication adoption. Conclusions: Adoption of pharmacotherapy was more likely in programs that had greater medical resources, Medicaid funding, and contact with pharmaceutical companies. Given the potential expansion of Medicaid under the Affordable Care Act, patients served by publicly funded programs may gain greater access to such treatments, but research is needed to document health reform's impact on this sector of the treatment system. (J. Stud. Alcohol Drugs, 75, 476-485, 2014)