1) Don't get too worked up about not being immediately successful. Long term stress isn't productive and will damage you. It really takes *a lot* of time to become a good programmer AND have someone you want to work for recognize it, if you're unconnected. I was the top 5% of programmers in my university classes, yet I it took some time before I got a good foothold in the labor market after aborting my studies. (In turn caused by my preference for doing programming rather than theoretical university assignments or studying for exams. Will finish my degree shortly in parallel with work.) Similarly, I spent some time doing Internet jobs (always receiving the highest grade by clients and reaching 0.1% best in world rankings), but honestly it didn't work out financially from where I live due to high costs of living. That in turn caused enormous stress as well.
2) I've never done drugs (unless coke i.e. Coca Cola counts, which I was drinking way too much of for a period). Can't give you any advice on this subject thus, other than the obvious "don't do it". The mind doesn't always take rational paths however.
3) Social anxiety is something I have but it gets better when I get out often among people - having a workplace helps. It has also improved massively with age, I'm very different now at 27 than I was at 21. Can't say whether that will apply to you obviously, but there might be hope. A problem with college is that it's possible to be very anonymous in some places; that's not possible in a small company's office.
4) Fix your education or get out and work for a bit, IMO. It just costs too much to stay inside college failing courses (easy to say in retrospect, it's hard to see it while you're there and feel you have an obligation to continue studying, ultimately I had to break up with all the expectations that had been laid upon me - even by myself). The quicker you can become honest with yourself about what you're really doing the quicker you will feel you're in control of your life.
This post risks being slightly rambling as well and unrelated to the thread title specifically I realize, but that's what you get with the original post. Overall my life has vastly improved since I was 21, and I felt I should share that optimistic outlook with you.