One major effect of the law is that it causes a massive inflation of the price. Farmers are poor. As soon as it gets into the hands of someone willing to cross a border with it and break the "law" it's magically worth up to one hundered thousand percent more!
Lets just say there were absolutely no drug laws, and drugs were valued for what they are, vegetables; what would the effect on society actually be? Would everyone be snorting cocaine all day?
I know one thing that would happen, crimes committed for the acquisition of drugs would decrease heavily. Junkies wouldn't need to commit as many burglaries if they can get a gram for 10 pence as opposed to £50.