Teens who smoke cigarettes or marijuana are at higher risk of developing symptoms of psychosis, according to new research published in the journal JAMA Psychiatry.
Previous studies have shown that adults who use cannabis regularly are more likely to experience psychotic episodes. And tobacco use has also been associated with increased psychosis risk, albeit to a much lesser extent. But is this the same for teens?
Researchers from the University of Bristol examined survey data from 3,328 teenagers who had answered questions on their use of cigarettes and marijuana.
The team found that those who had smoked cigarettes only at an early age were 4.3% more likely to experience a psychotic episode by 18 compared to those who didn't smoke.
Teens who had smoked cannabis only at an early age had a 3.2% greater chance of experiencing psychotic symptoms, compared to non-users. Furthermore, teens who had only used marijuana at a later age were 11.9% more at risk.
Armed with this data, the researchers took into account other factors that could influence the results, such as bullying, social class, alcohol use or family history of schizophrenia. In light of this, the link between smoking cigarettes and psychotic symptoms weakened.
"Our study found that both adolescent cannabis use and cigarette use are associated with increased risk for subsequent psychotic experiences, but the association was greater for cannabis," the authors wrote in the study.
"Associations observed between tobacco use and psychotic experiences are more likely than those for cannabis use to be influenced by other characteristics of people who develop psychotic experiences."
Importantly, the researchers concluded that they could not "rule out whether the associations observed between the cannabis use class and psychotic experiences are exacerbated by the combined use of cannabis and cigarettes".
However, the study was limited by the fact that it didn't control for people who already had a pre-disposition to psychotic experiences.
Psychosis is a mental health problem characterised by an impaired relationship with reality. Symptoms may include hallucinations, delusions or feelings of paranoia.
It is important to note that this study does not provide conclusive evidence that marijuana or cigarette use is directly causing psychotic episodes in teens, although some research has suggested this may be true. Scientists are still divided on this issue, with various studies both supporting and refuting the argument.