There are a number of things that you have to consider.
First of all, it's that drug companies, by and large, look at established markets. They see that there's a drug on the market and it has good sales, and they want to get a piece of that pie. They develop their own version of that product. They manipulate a few molecules and produce that new drug. Then they market that new drug very heavily to doctors. The last figures I saw showed that drug companies were spending about $450 million per year on their sales representatives and ads in medical journals. That's about $60,000 per doctor, per year, just on those two forms of promotion.
When you look at the regulatory requirements for approving drugs, you see that they don't have to be better than what's on the market. They can, in fact, be inferior to what's on the market. The only thing that's required to get a new drug on the market in Canada and in other countries is that they be better than placebos, and the amount “better” is marginal.