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Cannabis and cigarette smoking in teenagers

Tobacco and Alcohol Research Group, Bristol

Press release issued: 18 January 2018

Researchers within the School of Experimental Psychology studied 3,328 adolescents and found evidence that both cannabis and cigarette use are associated with subsequent psychotic experiences.

Researchers from the University of Bristol looked at family data for 3,328 teens living within the Bristol area. The teenagers were asked to answer questions about their use of cigarettes and cannabis at six separate time points between the ages of 14 and 19. As many people who smoke cannabis also smoke cigarettes, the researchers attempted tto discover the separate health effects of each substance. 

Analyzing this data, the researchers found a strong association between smoking cigarettes (only) at an early age and having a psychotic experience by the age of 18. These teenagers had a 4.3% higher probability of having a psychotic episode by age 18 as compared to teens who did not smoke. "Early" use or "late" use was not defined by an actual age. 

The team of researchers also found that teenagers who only used cannabis at an early age experienced a 3.2% greater chance of having a psychotic experience as compared to non-users. 

The most striking increased probability, though, occured among teenagers who only used cannabis at a later age. They had a 11.9% greater odds of psychotic experiences by the age of 18. 

As well as this, they also looked at other factors in each teen's life including alcohol use, bullying, social class and family history in order to see if these factors could of influenced the results. 

With all these additional factors included in the analysis, the researchers found that the relationship between smoking cigareettes ad psychotic-like symptoms weakened. However, the relationship between cannabis and psychosis remained strong. 

Predisposition to psychosis 

Strengths of the new study include a large number of participants, "very rigorous" methods and measurements, a high proportion of female participants - "which is not always common" - and longitudinal measurement, where the researchers do not look at data from "a single slice in time ebut over a period of 4-5 years" said Vadhan. 

Its weakness, according to Vadhan is that the authors of the study didn't account for people who already showed a pre-disposition tot psychotic-like experiences. 

Further information

Further details on the Tobacco and Alcohol research group can be found here

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