Executive Summary The release of clarified Food and Drug Administration (FDA) guidelines and independent changes in consumer behavior provide an opportunity to study the effects of direct-to-consumer advertising (DTCA) in the prescription drug market alongside the effects of various physician-oriented promotions. We examine the effects of DTCA and detailing for brands in five therapeutic classes of drugs, using monthly aggregate U.S. data from August 1996 through December 1999. In terms of

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... t of DTCA on demand, we provide evidence on two issues: (1) do increases in DTCA increase the market size of an entire therapeutic class? and (2) does DTCA increase within-class market share of advertised drugs? Our findings suggest that, for these classes of drugs, DTCA has been effective primarily through increasing the size of the entire class. Overall, we estimate that 13 to 22 percent of the recent growth in prescription drug spending is attributable to the effects of DTCA.