You might also find that psychology is... somewhat overrated I guess. If you did Psych, you would have to take a bunch of classes outside the realm of drugs that you might have no interest in whatsoever. If you're wanting to be in the drug realm, I would go into Chemistry. Like someone said before, a lot of people's opinions change about drugs, at this point in your life, do you really think that it is something you can pursue forever? If you have a degree in Chemistry, you can easily be employed...pretty much anywhere that makes stuff.
Edit: No matter what you do, start working in a professor's lab as early as you can. You'll learn through classes, but will learn what everyone else is learning, you'll get a huge leg up in your career by working closely with a professor, especially on paper if you have 2+ years of research experience as an undergrad.