*The following is excerpted from an online article posted on CNN.
For teens, using either marijuana or cigarettes is associated with higher odds of psychotic-like experiences, a new study published in the journal JAMA Psychiatry found. Psychosis describes the mental condition of losing touch with reality, such as experiencing hallucinations or delusions.
"Individuals who use cannabis regularly have a 2- to 3-fold increased risk of a psychotic outcome," University of Bristol researchers wrote in the study. Past research has calculated a statistical association between daily use of tobacco and an increased risk of psychosis.
The researchers wondered, are there differences for teens?
For the new study, the research team looked at family data for 3,328 teens living in the Bristol area of the United Kingdom. The teens answered questions about their use of cigarettes and cannabis at six separate time points between the ages of 14 and 19. Since many people who smoke pot also smoke cigarettes, the researchers attempted to discover the separate health effects of each substance.
Analyzing the data, the researchers found a strong association between smoking cigarettes (only) at an early age and having a psychotic experience by age 18. These teens 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 researchers also found that teens 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, occurred among teens who only used cannabis at a later age. They had 11.9% greater odds of psychotic experiences by age 18.
Next, the researchers looked at other factors in each teen's life -- alcohol use, bullying, social class and a family history of schizophrenia, among others -- to see if these might have swayed the results.
With these additional factors included in the analysis, the researchers found that the relationship between smoking cigarettes and psychotic-like symptoms weakened. However, the relationship between cannabis and psychosis remained strong.
The researchers also flipped their focus to see whether teens who had experienced psychosis during childhood showed increased cannabis or tobacco use. They found little evidence that early psychotic experiences led to increased use of either substance.