Prescription drug formulary design, preferred-product marketshare, and formulary noncompliance: a study of proton-pump inhibitors.

The intent of a prescription drug formulary is to shift utilization toward preferred products, but health plans must balance the benefit of these products' lower price with the cost of potential formulary noncompliance. Using proton-pump inhibitors as a model, the authors studied the influence of formulary restrictiveness and drug preference status on formulary noncompliance and marketshare. They found that although drug formulary restrictiveness increases the use of preferred products, it also leads to a high level of formulary noncompliance. The net financial effect on drug spending is ambiguous.