Citations, please.
A phrase to remember when citing anecdotes about mentally ill people taking Drug X is self-medication. This is a technical term in counseling psychology; it refers to a very common phenomenon where a person who is suffering a mental health issue -- which can be anything from a mild acute depression to full-blown schizophrenia -- figures out, by trial and error, that taking a certain drug seems to alleviate their symptoms, or make those symptoms more tolerable. This often causes the patient to end up with two health problems, which can be difficult to sort out from each other and which generally must be treated together.
So even if you uncover evidence that mental illness and taking drugs are correlated, you can't simply assume that the drugs cause the mental illness. It could just as easily be the other way around.