Cannabis is often the precursor of psychosis, especially paranoia. Anecdotally it seems to exacerbate psychotic moods and symptoms. My own view is that it cannot possibly benefit sufferers and it seems risky to prescribe it (if I have correctly understood the summary) at all. I remember Professor Robin Murray saying some years ago that cannabis was implicated in the causation of mental illness. Well, he should know and I don't suppose his views have become obsolete.