In that order: use, possession, manufacture, distribution
I think you will get a reduction in the number of people who would agree with having no restrictions. For instance, drug use is probably ok, but not while driving a vehicle, or playing a competitive sport. Drug possession is probably fine, but not more than X amount. Drug manufacture might be fine, if you are just growing/making for yourself. Drug distribution is probably not ok unless you have a license and follow state/federal guidelines.
I think where the law breaks down is under: 'possession'
If it's legal to possess say, 200 pills of oxy at any time, no Rx, no questions asked, I don't see how that isn't going to result in increased distribution.
Alcohol regulation obviously wouldn't change