Life Skills Education

Using cannabis for the first time under the age of 15 is linked to an increased risk of hallucinations or delusions, a new study has found. However, the findings are still not definite.

What do we know already?

Previous studies have found that using cannabis at a young age is linked to psychosis, a condition where someone loses touch with reality. Someone with psychosis might hallucinate or have false beliefs called delusions. Schizophrenia is one cause of psychosis.

Although cannabis use seems to have a link with psychosis, it’s harder to find out whether it’s the cause of the problem. The sheer number of things that could influence someone’s mental health makes it difficult for researchers to investigate whether cannabis really has an effect. Some doctors think people at risk of psychosis may be more likely to use cannabis because of problems in their lives, or to help them cope with their mental illness.

A new study solves some of the research problems by looking at siblings. Siblings usually grow up in a similar environment, and they also share many of the same genes. So, if siblings have a different pattern of cannabis use, researchers can be more confident that it caused other differences between them, such as differences in their mental health.

What does the new study say?

The study looked at nearly 4,000 Australian people born in the early 1980s. At 21 years of age they were asked about whether they’d used cannabis, and also completed questionnaires asking if they’d ever had symptoms like hallucinations or delusions.

People who’d started using cannabis before age 15 were more likely to have had symptoms of psychosis by the age of 21. Of the people who’d used cannabis at an early age, 3.9 percent had developed a psychotic illness. This compared with about 3 percent of people who’d started using cannabis after age 15, and 2.1 percent of people who’d never used cannabis.

The study included 10 pairs of siblings among whom one had developed a psychotic illness but not the other. Within these pairs, there wasn’t a big difference in cannabis use. However, among the 218 pairs of siblings where neither had developed a psychotic illness, siblings who’d used cannabis at a younger age tended to score higher on a questionnaire measuring “delusional-like experiences”.

The article continues here

Article taken from

McGrath J, Welham J, Scott J, et al. Association between cannabis use and psychosis-related outcomes using sibling pair analysis in a cohort of young adults. Archives of General Psychiatry. Published online 1 March 2010.

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