To evaluate the impact of a payor-initiated formulary change in inhaled corticosteroid coverage on lung function in patients with asthma and on provider prescribing practices. This formulary change, undertaken in August 2016 by a Medicaid payor in Kentucky, eliminated coverage of beclomethasone dipropionate, a metered dose inhaler (MDI), in favor of mometasone furoate, available as MDI and dry powder inhaler (DPI).