We treat the population too much like children. Let people make their own decisions. If it kills them, it kills them. They made their choice. If they want help, they'll seek it on their own.
If you become a public nuisance, and/or threaten or injure people due to the influence, those are also obvious offenses.
If you drive under the influence of chemicals that reduce your motor skills and reaction time, and alter your perception of reality, that is an obvious offense.
Other than those cases which we can almost all agree should be intervened, why are we telling people what they're allowed to do with their bodies?