Prohibition didn't work on alcohol. It just generated revenue for organized crime syndicates. Doctors could legally prescribe booze back then too.
There will always be a small percentage of the population that abuses or becomes addicted to certain substances.
My mom was a marijuana addict for many years self medicating her schizophrenia. The fact that it was illegal just added another layer of dysfunction to my childhood because I was always terrified she'd get busted and we'd have to live full time with my alcoholic father.