To play devil's advocate, imagine a drug that costs $1b to develop and would only break even in costs - obviously drug companies wouldn't pursue the drug. But suppose spending $1b to develop and then $2b to market the drug does better than break even - possibly way better, with the right advertising agency. Then the drug company would pursue the drug. So advertising can lead to more drugs being developed overall, since it can do so much to improve the cash flows that accrue to any given drug.