 Bipolar disorder is a severe mental illness affecting about 3 of the U.S. population that causes personal suffering, morbidity, and premature mortality. Continuous access to medications, close monitoring, and other psychiatric care are crucial for avoiding complications of bipolar disorder such as relapse, hospitalization, and suicide. To control rising costs, payers and employers are increasingly adopting high-deductible health plans HDHPs with very high out-of-pocket payments. Federally-defined Health Savings Account HDHPs require full cost-sharing for all non-preventive services, including medications and specialist visits; family deductibles for HSA-HDHPs range from 2,500 to 12,700. Enrollment in HDHPs quadrupled nationally between 2006 and 2013 to 38 of all workers. Analysts expect further explosive growth because of continued health care cost pressure on families and employers. Well-informed patients in HDHPs might reduce use of unnecessary services and more expensive treatment options. However, patients might also choose to forego needed care. There is very little evidence on how particularly vulnerable patients such as those with bipolar disorder or other chronic mental illnesses fare when forced to make complex choices about spending for care under HDHPs. Given their rapid escalation, there is an urgent need to understand how vulnerable patients change their patterns of care and medication adherence under HDHPs. We will compare patients with three types of insurance: traditional plans with low or no deductible; HDHPs in which chronic medications are paid fully out-of-pocket until the deductible is met; and HDHPs where medications are subject to the same co-pays as in traditional plans. 