 Our research will provide empirical data comparing how patients with bipolar illness fare under three insurance designs with vastly different requirements for cost-sharing. At a time when HDHP enrollment is exploding, the experience of patients with serious mental illnesses is largely unexamined. Advocacy groups will be able to use our findings to lobby for more patient-responsive benefit designs; policymakers will have evidence to redesign insurance benefits to better address the needs of vulnerable patients e.g., by exempting mood stabilizing agents from deductibles. 