 Investigators will include health plan members aged 12 to 63 years at the beginning of the baseline period. Consistent with prior research,89-91 we will use medical claims data and a validated algorithm to identify members who had at least two ambulatory encounters or one hospital encounter with a diagnosis of bipolar disorder. Intervention cohorts will include traditional plan members with bipolar illness who experience an employer-mandated switch to HSA-eligible HDHPs with full drug cost-sharing or to HSA-ineligible HDHPs that subject medications only to copayments as in traditional health plans. 