I started having visual and auditory hallucinations when I was 18. These gained in severity, and eventually I was diagnosed as psychotic by a psychiatrist. However, at the time, I was very underweight, anaemic, had a very swollen belly and had constant diarrhoea. None of this was taken into account when I visited the doctors and psychiatrist. In the end I visited a naturopath, who suggested that all the mind symptoms were linkned in to what was happening to the rest of my body. I had the Celiac blood tests and biopsy, and turned out I was a severe Celiac.
Slowly after starting the gluten free diet the hallucinations have gone, and I feel more and more like my former self. There are a great deal of articles online about how psychiatric symptoms can be caused by a physical illness, and from my experience, I would say doctors should consider the possibility of physical illness causing the symptoms, before definitely conluding it is a primary psychiatric condition.