We study the equilibrium effects of introducing competitive bidding in drug procurement. In 2019, China introduced a competitive bidding program in which drug companies bid for a prespecified procurement quantity in nine provinces. Using a difference-in-differences design, we show that the program reduced average drug prices by 47.4%. Generic drug firms won most bids and cut prices by 59.4%. We develop a model of demand and supply to quantify the trade-off between lower prices and potential choice distortions. Competitive bidding increases consumer welfare if policymakers consider brand preferences welfare irrelevant. The program also reduced government expenditures on insurance by 27.5%.