OBJECTIVES: Step therapy is defined as the practice of beginning drug therapy for a medical condition with the safest and most cost-effective drug therapy and progressing to more risky or costly therapies. This analysis assessed the number of US health plans that require patients to step through a branded boxed warning product before initiating a branded non-boxed warning product.  METHODS: This cross-sectional analysis was conducted using formulary data compiled by the MMIT Formulary Analytics Specialty Assessment database, which includes 2015 formulary status and policies for all US health plans. Of the 27 therapeutic classes that include products with a boxed warning, 9 therapeutic classes met all of the following criteria: (1) include currently marketed branded products, (2) include branded boxed warning products, (3) include branded non-boxed warning products, (4) include specialty or small-molecule products. Formulary requirements and restrictions for the 30 largest commercial US health plans were examined for cases in which patients are required by formulary design to step through a branded drug with a boxed warning before initiating a product without a boxed warning.  RESULTS: The 30 commercial plans represented 121 million lives, or 56% of the 217 million commercial lives in the United States. The number of health plans requiring patients to step through a branded boxed warning drug before initiating a non-boxed warning product in the 9 therapeutic classes included were: anti-infectives (miscellaneous), 0; anticonvulsants, 0; antidiabetics, 0; gastrointestinal agents, 0; immunological agents and biologics, 18 (45% of covered lives); respiratory agents, 0; dermatologic agents, 0; central nervous system drugs (anti-Parkinson), 0; and renal agents, 0.   CONCLUSIONS: The designs of US formularies generally do not require a step through products with a box warning prior to initiating a product without a boxed warning. The one notable exception is the class of immunological agents and biologics.