In my opinion, I think there would be a slight increase in usage mainly because of the media coverage there would be around illict drugs being legalised, after a while I think it would eventually be stabilisation. If the illict drugs were legalised than they would have to cut down on law enforcement since there wouldn't be as much crime going on anymore. 'Drug dealers' would be turned into business man, and layed off law enforced would be able to find jobs in a new market because they most likely have a good deal of knowledge about the substances and on top of that medical professionals would be able to do proper research.