Is there a link between

Cannabis and Psychosis?

Yes, although it is complex. Cannabis use is one factor that has been associated with an increased risk of developing a psychotic disorder. Usually, it is a mix of frequent, heavy cannabis use, especially in adolescence, and a and a history of mental illness in one’s family that is considered the riskiest combination.


According to Health Canada, the risk with use varies from 2.5-10 %  depending on factors such as family history of mental illness, age at which cannabis use starts and THC content of the cannabis.


Specifically, regular cannabis use in adolescence:

  • is linked the development of a long-term psychotic disorder in at-risk individuals.
  • is associated with an earlier age of onset of psychosis.
  • can complicate and/or prevent recovery in individuals already diagnosed with a psychotic disorder.


For a more in-depth overview of the research, please see Health Canada’s review the literature here. A recent “review of reviews” is also available here and finds that:

“The scientific literature indicates that psychotic illness arises more frequently in cannabis users compared to non-users, cannabis use is associated with a dose-dependent risk of developing psychotic illness, and cannabis users have an earlier onset of psychotic illness compared to non-users. Cannabis use was also associated with increased relapse rates, more hospitalizations and pronounced positive symptoms in psychotic patients.”

What are some of the effects of cannabis

on the developing brain?

The THC  with Cannabis binds to receptors in the brain to produce the “high” that people experience. This binding action may overrule the natural function of these receptors.

Why does cannabis use affect mental health especially

if use starts in adolescence?

The answer is tied to brain development. The brain begins developing in-utero and continues developing up to about age 25. This happens in stages – basically starting with the brain stem and the cerebellum which are closer to the back of the head. This area controls basic body functions such as breathing, swallowing, heart rate, blood pressure, consciousness, and whether one is awake or sleepy.  Development continues towards the front of the brain with the prefrontal lobe which is at the very front of the cortex, which develops last. The prefrontal cortex is a part of the brain that is responsible for a variety of complex behaviors, including memory, attention, flexibility, planning, problem solving, decision making and social behavior as well as contributing to personality development.


We all have cannabinoid molecules created inside the brain and the rest of the body that are part of our endocannabinoid system. This system plays a part in performing biological functions. In the developing brain, the receptors that bind to these biological cannabinoids are used to guide brain cells to make the connections needed for regular brain function and development.


Plant cannabinoids such as THC and CBD bind to these same receptors Research suggests that THC creates a large amount of signal that comes from inhaling or ingesting cannabis, overwhelming the normal brain development process. The reason adults over 25 are not at the same risk is that these cannabinoid receptors have done their job finishing brain development and then research suggests that this function is turned off by the cannabinoid receptors changing their pattern of expression (where in the brain the receptors exist). However, it is important to note that, while brain development seems to occur differently in cannabis users, it is not always clear nor consistent which brain structures are affected and what this means for cognition and functioning. It is also difficult to disentangle the effects on the brain caused by alcohol from those caused by cannabis.