The Rough Guide to Psychology An Introduction to Human Behaviour and the Mind (Rough Guides)

THE ROUGH GUIDE TO PSYCHOLOGY

and mental health campaigners oppose this idea. They point to the
statistics showing how rare it is for a mentally ill person to harm other
people, and they question the morality of imposing drugs that often have
serious, unpleasant side-effects. In all this debate about schizophrenia
and violence, it’s also worth remembering one sad, undisputed fact that
often goes overlooked, which is that someone with a diagnosis of schizo-
phrenia is at increased risk of being a victim of violence. For further
information on the issues surrounding mental illness and psychosis, the
British Psychological Society produced a free booklet, which although
published over ten years ago, remains useful (tinyurl.com/lt4xnl).

Does cannabis cause schizophrenia?

This has proved a tricky question to answer. There are certainly reasons

to think it might. An authoritative meta-analysis published in 2007 by

Theresa Moore of the University of Bristol combined the results from

eleven longitudinal studies, and concluded that heavy users of cannabis

were between fifty and two hundred percent more at risk of developing

psychosis than non-users. Among users in general (light and heavy),

the increased risk was forty percent. If we assume that the link is causal

• that smoking cannabis brings on psychosis in people who wouldn’t
  otherwise have developed it – this would equate to 800 extra cases
  of psychosis in 15 to 34-year-olds every year in the UK. So, what’s the
  caveat? The problem with research of this kind is that it’s very difficult to
  know whether the cannabis users in these studies would have developed
  psychosis anyway even if they hadn’t taken cannabis. In fact, there’s
  evidence that people who exhibit very mild psychotic-like symptoms are
  more likely than average to begin smoking cannabis, perhaps as a form of
  self-medication. Another problem is that the intoxication associated with
  taking cannabis can bring on acute psychotic-like symptoms. This can
  make it difficult to establish whether cannabis really triggers long-lasting
  psychosis beyond the period of intoxication.