Oh, btw, those under 21 already account for a high percentage of users and would be unaffected by any change in the law. Actually, if history is any guide, their numbers would increase if marijuana were legalized for adults (happened in Alaska).
That was an easy question, you're baiting me right?
First, I would apply legalization to all drugs. Those like cocaine and methamphetamines would be labeled "Poison" and anyone who dies as a result of their abuse will have said to committed suicide. I will expound at end...
Second, by legalizing all drugs you have done the following: Removed a lucrative black market that has turned our inner cities into factories of death. You don't see kids selling alcohol and ciggarettes on the street, and if they did.. they don't make enough money to finance gangs and their weaponry. Everybody has heard of Al Capone and for that matter Joe Kennedy (father of Kennedy Clan). You would never had heard of them if alcohol hadn't been prohibited at one point.
Third, the only reason "numbers" increased as you say they did in Alaska is because people would not be hesitant to state they used it in a survey once it was legal.
Fourth, Everyone knows where to get pot or someone who can get it. Go ask any kid of any age and they will tell you who to get it from. It's all over the place, there is no avoiding it. It is so prevailant that it would be impossible to get rid of... how has the "War on Drugs" done so far? Nothing... 100s of billions upon billions of taxpayer dollars spent... 70% of our prisoners up on drug charges... and there has never been a reduction in supply or use.
What to do if legalized:
1. Make it a felony to give drugs to minors. Just like alcohol should be. I remember it being difficult to get booze and easy to get drugs in high school.
2. All Under the influence laws would apply.
3. Tax it and spend taxes on rehab and education.
4. Legalize all drugs with massive spending on advertisements explaining what they do. Poor kids in middle America are destroying themselves with paint, gasoline, and glue... all readily and legally available.. but with no idea what they are doing to their brains.
5. Those who die as a result of drug use will have been considered to have committed suicide (no life insurance applies)
I say either make everything Illegal and show me how you prevent it from being used and being a lucrative black market that generates 80% of the crime and gun deaths in our society, or make it legal and as safe as you can. I cannot see supporting the current Status Quo at any rate... This drug legal, this drug illegal... War on Drugs that can never win given any scenario....