This application, High deductible health plans: substance abuse service use and cost trajectories, responds to PA-08-174: Economics of Treatment and Prevention Services for Drug & Alcohol Abuse (R01). We propose to examine the impact of high deductible health plans (HDHP) on utilization, costs, and outcomes of patients with substance use (SU) problems over time. We have a unique opportunity to study these questions as Kaiser Permanente Northern California (KPNC) is currently implementing HDHPs. We first examine selection effects in patient characteristics of SU intakes with (and without) the HDHPs across five years (2006-2010) using clinical and administrative health plan data and the electronic medical record (EMR). We then examine 3-year trends in utilization of SU treatment services, medical services, and health care costs by HDHP status for a sample of members who had an intake to SU treatment between 01/2006 and 06/2007 (n=16,313). Finally, we conduct a telephone survey of a cohort of SU treatment intakes from 2009 (n=400) to examine patient knowledge of the HDHP benefits, SU outcomes, and care-seeking behavior in the face of high cost-sharing. This research addresses a key scientific and policy issue: utilization and cost and outcomes of SU treatment in a health care environment that has increasingly turned to HDHP products to control costs by shifting costs to patients. Demand for SU treatment is seen as more price-sensitive than medical care and SU benefits are more limited with higher cost-sharing. This can potentially delay treatment seeking, with increased disease severity and costs over time. The SU population has unique characteristics, including high comorbidities, that may raise the patient risk profile under HDHPs. These individuals often have unanticipated costs such as emergency room visits due to injuries or overdoses. The study is innovative in its use of information technology, including the EMR to examine study questions, and for its clinical implications. Access to the health plan's web-based Outcomes Monitoring System provides baseline epidemiologic information on SU at intake to treatment, enabling a follow-up outcomes survey. We use propensity score analyses to model selection effects and hierarchical linear models for longitudinal analyses. HDHPs are increasingly available and findings have important policy implications outside of KPNC. Findings may improve access to SU treatment, outcomes, reduce costs, and improve patient education and activation. Policy implications include changing benefit designs to include SU treatment as a high value health care service, with low co-payments, or embedding SU treatment services in primary care.