Personally I like the concept of legalize, regulate, and tax!!
Create taxes based on two criteria:
addictiveness: the higher the level of addictiveness the greater the tax
deadliness: the greater the risk of death to oneself or another the greater the tax.
In all cases any 'drug' would be seen as having additional taxes that would go towards enforcing regulations, educating people on drug use, recovery programs, research, and assistance to people who have a medical need for a drug.
This may get tricky with items such as caffeine and in regards to dealing with OTC medications and prescription medications. This would have to be worked out.
Any TOTAL Illegal drugs still?
Usually my own mind immediate jumps to drugs such as heroine and cocaine. However, I wonder if it is wise to make these continue to be illegal versus having them be extremely taxed and regulated.
Create laws against use while driving, limiting use to specific places (ie homes, licensed "parlors", or similar). Create limits on purchasing to control usage to a degree. Fines when a person is caught with more than the acceptable amounts. And truly the ability to enforce these regulations is key.