How do I know this?
I have mental illness in my family and have spent considerable amounts of time at those facilities.
So many questions.
Where is the medical journal that says your conclusion "vast majority of mental health patients have a self-reported history of drug use of these specific drugs". I guess it can't exist because its crazy people self reporting a variety of substances that even the user would have no idea what was actually given to them.
What? How is it clear? As you wrote yourself, correlation is not causation.