Drug education should be taught throughout school.
Once old enough you should then go on a drug education course, covering things in more detail, the dangers, what to do in event of overdose, etc. When you pass the course you are given a license (much like a drivers license) that will enable you to buy a certain amount of drugs in a time period (with a chip and pic type device).
Boom. The criminal underworld that has control of the supply of drugs will lose it's grip. People will stop falling dead from adulterants they didn't even want to take or accidental overdoses caused by fluctuating purity. The average joe on the street will be a lot more clued up on how to deal with different types of overdose. People will be PROPERLY educated on drugs. Money saved and money made would massive.. this could be spend on better healthcare, education, etc and on better, proper treatments for addicts, and better research on drugs. And so on. The list is fckin endless.