How does advertising prescription drugs make money?

Why are there so many advertisements for prescription drugs on TV? How does that work? Who goes to the doctor with a drug they're expecting to get? It just seems to me that the doctor would know better about the drugs they're prescribing than what I get from a 30 second ad. Do people really go do the doctor and tell them they want a specific drug? It just seems kinda pointless to advertise to the people who aren't making that decision, rather than to the doctors themselves.