Schizophrenia is a common mental illness, affecting around 1% of the population. The link between cannabis and schizophrenia has long been debated and researched, and often appears in the news. However, perhaps a lesser known fact about schizophrenia is that developing it at a young age is associated with a poor outcome. People who are diagnosed with schizophrenia earlier on life are more likely to have more problems with cognition. They will also spend more days in hospital each year and are less responsive to antipsychotics.
There are several known factors which affect the age of onset of schizophrenia. Being male appears to be one, with males being 1.63 years younger than females when they first experience symptoms of psychosis. Smoking cannabis, which is often seen amongst people experiencing their first episode of psychosis, is also known to be associated with earlier age of onset of psychotic symptoms. However, cannabis use is more common amongst males with psychosis than in females, so which of these factors is causing the early onset of symptoms is not clear. A study coordinated between several UK universities including Kings College London, Nottingham and Cambridge, as well as Verona, Italy, investigated how gender and cannabis use affect the age of onset of schizophrenia. They aimed to find out whether males develop schizophrenia earlier in life because of their increased cannabis use, or whether it was cannabis itself which causes symptoms earlier in life. The research was published last month in the journal Psychiatry Research.
The research analysed data from 143 people who originally took part in the ÆSOP (Aetiology and Ethnicity of Schizophrenia and Other Psychoses) study. This was a multicentre centre study taking place in Nottingham, Bristol and South-East London which aimed to discover risk factors which predict the outcome of a first episode of psychosis, focusing specifically on social factors such as ethnicity and cannabis use. As the research was looking at factors affecting an early age of onset, the people included in the study were all aged between 16 and 45. Out of the 143 including, 85 (59%) reported that they had used cannabis at some point.
As expected, people who used cannabis were younger when they first developed psychotic symptoms, and more males reported using cannabis than females. Although males who did not use cannabis were still younger at age of onset than females who did not use cannabis, there was a similar age of onset amongst both males and females who used cannabis.
Professor Peter Jones from the Department of Psychiatry who worked on the study said, “The results are important in that they contribute to our understanding of the relationship between cannabis and schizophrenia. Those who used the drug, and particularly young women, had a younger age at onset of their illness. This may help explain why the outcome of people with schizophrenia who use cannabis is worse than those who do not. The mechanisms of that effect may involve multiple domains including dependence, the effects of chronic intoxication, restriction of social, occupational and educational aspects of social capital and direct neurotoxic effects. Helping those with schizophrenia to limit or stop using cannabis remains an important goal.”
This research was funded by the Medical Research Council.