I know there are some prescription drugs that can reduce hearing, but they're standard drugs like Ibuprofen, if you're old and take lots of them. I think. I've never heard of any illegal drugs having that effect..

As to RSI being psychological... after Googling around a bit I find a handful of (paraphrasing) "RSI may be to some extent influenced by stress", but nothing that it is 'entirely psychological'? Can you cite sources?