If all drugs are decriminalized (keep in mind I am not saying legalized) then the options for other drugs that are less dangerous and addictive would wipe those out, especially meth. Additionally addicts would seek help and be allowed help without being thrown in jail or given fines. If you actually want to read about a country that has done it look at Portugal and what they have done. Their policies have reduced heroin users drastically and the few that are left are generally known to the government and they are in treatments or getting help in some way.
