Canada's the same way. Our taxes pay for Health Cards which offer free health services, but medecine costs a lot if you don't have insurance from your work - especially dental-related things.
Rehabilitation would be an issue, but I don't believe marijuana would lead that many people to more dangerous drugs. Only the stupid people, really. A lot of people view it as a "gateway" drug, but everyone I've ever talked to only take weed - everything else they deem disgusting, abused, dangerous, and unhealthy. From personal experience, Canadians don't go Marijuana->Cocaine->Heroine->Death, so it's not really a problem over here. Maybe that's because our weed doesn't have chemicals topped on it :< I'm not sure...