That's certainly arguable, but let's just say, for one moment, that you are correct in that assumption. Seems to me they are not doing a very good job of it. In fact, FedGov sucks in general at any kind of prohibition, apparently. Seems like prohibition only leads to higher crime rates, black markets and promotes general discord. Apparently, you don't care for the rule of law, seeing as how you yourself support black markets and higher crime rates.
Really? Compared to what? According to DrugLibrary.org, Opium usage in China was at 50%.
Then, in 1906, the incredible happened. After over a hundred years of steady demoralization, with half her population opium addicts, or worse still, making enormous profits out of the trade, China determined to give up opium.
I will point out, "DrugLibrary.org" is a pro-drug legalization web site.
So is our percentage of the population using drugs around 50%? If not, then It would appear we've been having quite a lot of success.