Can we stop people taking drugs. No.
Can we (the government) advise there may be physical and mental consequences for some. Yes.
I would go down the control and tax route. Try it for 3 years and see what happens. The system we currently have in place clearly isn't working.
Tax take could be considerable.
I think the lady in your avatar would have your balls for that statement, and that's the problem. Too many who can't see the practicalities for their moral judgments.
As I said earlier, the dealers would change their business model to target under 18,s much more, and sell product which is much stronger than the safer legal stuff. Not much would change in reality. The police have decriminalised most drugs in all but name by turning a blind eye to most of its use, but it hasn't helped matters at all.
As for informed choices. Can you call a 14 or 15 year old smoking skunk at school with their mates, because they desperately want to fit in an informed choice ?
Nah, shooting the dealers and importers (cutting the head off the snake) is the only real answer.