(2) what assessment he has made of the evidence linking cannabis use and the onset of schizophrenia in the 15 to 25 year age group;
(3) what assessment he has made of the changes in incidence of psychosis in 15 to 25 year olds in the last 30 years.
It is difficult to assess the trends in incidence of psychosis or schizophrenia for this age group over the last thirty years due to the relatively small numbers of people suffering from these conditions. This makes any assessment of statistical significance of a change vulnerable to error. Also during this time diagnosis classifications have changed for these conditions, which could mean that comparisons over this period would not be measuring like for like.
The Department is concerned about the negative impact of cannabis use and intoxication on acute mental health patients and on mental health services, and about the increased evidence for a possible role for cannabis in the causation of longer-term disorders such as schizophrenia.
The Department advises that cannabis use is harmful for people with existing mental health problems, being linked with relapse and resistance to treatments.
Research data also indicate that the impact of cannabis is likely to be on those already vulnerable to onset of schizophrenia.
It is also recognised that cannabis can cause an acute, short lived psychosis, from which the person recovers quickly following cessation of cannabis use but which, in severe cases, may require a short period of inpatient care. We keep the evidence and research in this area under constant review.