Age-Specific Psychotic Effects with Cannabis Use

There is increasing evidence that some users of cannabis may be vulnerable to adverse cognitive effects including psychotic symptoms. Many adult casual users of cannabis appear to have minimal cognitive effects. However, younger users and those with underlying mood or psychotic disorders may experience significant adverse consequences of regular and heavy cannabis abuse. A previous post linking cannabis-related psychosis to family history of psychosis is posted here.

Schubart and colleagues in the Netherlands and UCLA recently analyzed the rates of reporting psychotic experiences in European (primarily Dutch-speaking)adolescents and young adults. They looked specifically for the rates of endorsement of psychotic and mood symptoms in adolescents grouped by frequency and quantity of cannabis use.
Psychotic symptom experience is commonly grouped into what are known as positive symptoms or negative symptoms. Positive symptoms of psychosis typically include delusions, auditory hallucinations and visual hallucinations. Negative symptoms of psychosis typically include loss of motivation, withdrawal, and lack of goal directed productivity.

Over 17,000 young adults participated in the survey with over two thirds of the respondents being classified as users. Looking at the entire group of regular cannabis users, their scores on measures of psychosis and depressive symptoms did not differ from those who reported not using cannabis.

However, two factors among the users identified subgroups with signficant endorsement of symptoms of psychopathology:

• Cannabis users who initiated use before the age of 12 were three times more likely than non-users to be in the top 10% of scores on psychotic positive symptoms
• Regular heavy cannabis users (greater than 25 euros spent per week on cannabis) were 2.8 to 3.4 times more likely to be in the top 10% of scorers on scales of positive and negative psychotic symptoms as well as depressive symptoms.

The authors noted in the discussion that this cross-sectional design can not prove a causal pathway. It is possible that young people with psychotic symptoms may be more likely to begin using cannabis. Additionally, they note that young age of onset of cannabis use may also indicate a larger cumulative exposure that could be related to psychotic and mood symptoms.

However, they do note their findings are consistent with the possibility that tetrahydrocannabinol (or other cannabis drugs)may have increased toxicity "during critical phases of brain maturation". There may be a window of vulnerability to the effcts of cannabis. Use after passing through this window, limited cannabis use may have limited cognitive effect. Early cannabis use and heavy chronic use may be a much different story. 

Photo of a black and yellow argiope spider from North Palm Beach Florida courtesy of Yates Photography.

Schubart CD, van Gastel WA, Breetvelt EJ, Beetz SL, Ophoff RA, Sommer IE, Kahn RS, & Boks MP (2010). Cannabis use at a young age is associated with psychotic experiences. Psychological medicine, 1-10 PMID: 20925969