The pharmaceutical industry is highly competitive. So much so, that a slip in production or a legal hold up can lead to a competitor developing a similar product first, and subsequently, hundreds of millions of dollars lost. Canadians generally don't see this competition because much of the marketing is done by pharmaceutical representatives directly to doctors. Also, it's illegal to advertise both a drug and it's purpose in Canadian television or printed material (while Britain's banned pharmaceutical advertising entirely).
When successfully marketed, one drug can gain momentum, getting prescibed more than other perhaps more effective treatments. Ritalin, Prozac and other overprescribed drugs are excellent examples of this
But if prescription medications are so competitive, why aren't they compared and rated like other market-driven products? Cars, banks, books, movies, restaurants, and schools all get ranked and compared, and people often make decisions based on that information.
Well... several websites have cropped up to answer that very question. They rate drugs in terms of efficacy, off label uses, side effects, prescription rates, dependancy, and more.