 Using ten years of data from the largest U.S. commercial health insurer 70 million members in all 50 states, we will assess the impact of HDHPs on key outcomes for patients with bipolar disorder experiencing employer-mandated shifts from traditional insurance to HDHPs. Our specific aims are to evaluate: 1 changes in medication adherence, and in intensity and quality of other health care; 2 changes in adverse events; and, 3 changes in patient out-of-pocket costs. We will compare how these outcomes differ for patients in HDHPs with and without medications subject to the deductible. We will assess effects in the overall population of patients with bipolar illness and in specific vulnerable subgroups, including racialethnic minorities, poorer patients, rural patients, and patients with other important comorbidities. 