by legalising drugs you will only get more people trying it keep it illegal.
Smoking rates are decreasing and that's not illegal. Education is the key, not prohibition. And I think the majority of people who start drugs do so because they feel rebellious doing something illegal. Take away the rebel factor and you remove the desire for a lot of people. Same as smoking - it used to be thought of as cool and tough - that isn't the case any more, which is probably why the number of people of young people smoking has decreased so much.
Education and treatment is much more effective than prohibition