It is clear that the abuse of drugs is a very serious societal problem with consequences for the Society of a country and the economics. I would have to wonder exactly how sound our current policies are with regard to both effectiveness and the cost efficiency, although in this sort of issue the calculations of true costs are quite beyond simple calculations. The basic question in my mind is whether or not you should be focused on enforcing the laws against substance abuse or if you need to be more focused on the issues of drug rehab and drug treatment. It is hard to imagine a really rational defense of our current policies in my mind, because they simply have not been the least bit effective. There are plenty of reasons to put people in jail and in some instances you should put people into jail for drugs, but the fact is that this does nothing to address the problem when you put a common drug user into prison.
The simple fact is that if you put a drug addict in prison, he just becomes a drug addict with access to all the information he needs to become a real criminal. People routinely go into prison after leading fairly productive lives and then come out as full blown felons. It is not that black and white obviously, but the simple fact is that you are not solving the basic problem by sending most drug criminals to prison. Obviously it is not as though treatment or rehabilitation is going to be successful every single time, but it is something which you can make the drug suspect pay for out of their own pocket. The rest of society has to pay a huge price to put the exact same person into prison.