If the US decides to ever take a science/evidence-based approach to addiction issues, it should drop. The US being the US, I expect things will get worse as religious fundamentalists and anti-science morons continue to beat addicts down rather than help them.
Not sure why you think pot legalization will be a negative, jdooner. It's not physically addictive like other substances and is already widely available - I expect it'll just reduce profits for organized crime and end violence related to the black market for marijuana. Put anything addictive in front of me and I'm on it like white on rice, but put pot in front of me and I can take it or leave it.
If anything, decriminalization or legalization of substances should reduce addiction - it makes addicts less likely to fear approaching medical professionals and opens up the possibility of treatments that aren't possible under prohibition. As an example, heroin maintenance therapy has been shown to be an excellent way to deal with the most difficult-to-treat heroin addicts, resulting in a sharp reduction of overdoses, disease, and increases in employment and housing stability. It also cuts out the market for heroin dealers (why buy from Mr Streetcorner with proceeds from property crime or prostitution if your MD can write you a scrip for clean junk?). One of the four founders of Johns Hopkins University (William Halsted) spent his life addicted to morphine, but was able to function as a doctor because he could just write up a scrip for himself - that would not fly nowadays and I'd expect he'd just wind up on the streets.
This isn't speculation - Portugal decriminalized everything and saw something crazy like a 50% reduction in addiction. The UK used to use heroin maintenance therapy and discontinued it under pressure from the fine folks in the DEA and subsequently saw addiction rates go through the roof.