well lengthy jail terms ust give the state more inmates and a larger expenditure. No effect on drug use.
If people are afraid of psycho high people doing crazy stuff it might be more helpful to to ban guns and other sorts of weapons. Also some legislation against operating machinery or driving under the influence will prevent accidents.
Just like alcohol you can't prevent drgu use. maybe it would just be smarter to legislate how you are allowed to do it. Mess with the method, not with the choice of doing it or not.