Psychiatry Paradox
I think that it comes down to the complex way in which mind is not just dependent on a brain, but the chemicals arising within the brain, especially the neurotransmitters. In particular, dopamine is believed to be implicated in psychotic disorders and serotonin in depression, and there are probably other chemicals which are involved.
What may be interesting for thinking about the mind and body problem is the way emotions work, especially in mood disorders. Treatment for depression often involves antidepressants, and these seem to be very powerful. I can say this on the basis of working with patients who were diagnosed with depression, and I have also taken antidepressants myself. However, what is interesting is the way in which mood can be affected by drug treatment but also by experiences. Life experiences affect moo strongly, as well as the way we process them, which is the basis for various therapy options.
On a slightly different level, we can think about psychiatry and delusions. It does appear that there is a genetic basis which predisposed people to psychotic disorders, and stress can be a factor. Use of recreational drugs also can be a trigger, especially cannabis. So, there is a definite chemical basis for psychotic disorders. However, it also involves the nature of thinking, which is based on chemicals and the brain. However, ideas come into play, and so we could say that delusions may even be seen as being a philosophy problem.