I don't believe it has been PROVEN, but one side effect of the drugs Rush was using is hearing loss.
We know that. But I don't think it is smart to purport that his hearing loss was CAUSED by drug use.
It could be any number of things that caused it. The age and health of a person, what type of field they work in, and what type of medications they're on, or a combination of all the above. What Rush suffers from, Autoimmune Inner Ear Disease, is caused when the body's immune system attacks cells in the inner ear that are mistaken for a virus or bacteria. AIED is a rare disease occurring in less than one percent of the 28 million Americans with a hearing loss.
It's hard to diagnose, but once the hearing is lost in one ear it will quickly spread to the other. That's the only tell-tale sign of Autoimmune Inner Ear Disease, and precisely what happend to Rush's hearing.
It's interesting that a Google search on "Oxycontin, hearing loss" doesn't come up with one legitimate medical site just a bunch of news articles, most of which happen to mention Rush Limbaugh, and one half-assed med-help-chat site.