A recent article published in the Child and Adolescent Psychiatric Clinics of North America (“The Changing Legal Landscape of Cannabis Use and Its Role in Youth-onset Psychosis”) sought to examine the relationship between cannabis use and psychosis in adolescents amidst the background of modern-day legislation and culture.1


The authors of this journal publication strove to highlight the increasingly apparent association between cannabis use and psychosis, those in society who are most vulnerable to this association, and the role of current changes in cannabis legislation that may play a part in fueling the increasing incidence of these cases. They then sought to provide clinical recommendations concerning both the prevention and treatment of those patients who are affected by psychosis.

An Overview of Psychosis & Schizophrenia

Psychosis is characterized as a symptom of either a disease process (psychiatric disorders such as schizophrenia, mania, and depression) or an adverse reaction to a medication or substance.

There are both “positive” and “negative” symptoms of psychosis and schizophrenia. Positive symptoms in this context can manifest as hallucinations, delusions, illusions, and disorganized thought or speech processes. Negative signs within this context can manifest as “flat affect” (reduced or absent facial expressions), alogia (reduced speech due to impaired thinking), as well as anhedonia (reduced pleasure in previously pleasurable activities), avolition (reduced ability to initiate purposeful activity) and apathy.

Schizophrenia is a psychiatric disorder that is characterized primarily by psychosis, which can be present constantly or sporadically throughout the condition.

Both men and women are equally affected by this condition, with the onset of the disease usually occurring during the early 20s for men and in the late 20s for women.7,8

Those who are acutely suffering from psychosis are typically treated with hospitalization. In contrast, those who have schizophrenia usually are managed via a multidisciplinary approach that involves pharmacotherapy (an antipsychotic medication) and psychoeducation (psychosocial therapy, education, and social support).

Cannabis Legislation and Culture

It has been 24 years since the first US state law was passed in 1996, allowing the use of medicinal cannabis.1 Since that time, 33 US states have legalized medicinal cannabis. 11 States currently allow cannabis for recreational use.1

Current statistics show that 18.4% of adolescents and 32.6% of college students in North America report using cannabis in the past 30 days.1 This was noted to be part of a consistently increasing trend in cannabis usage that started a few decades ago.

The authors drew a link between an increase in cannabis usage, in particular, reference to young adults and children, with the increasing prevalence of its legalization within North America throughout the last two decades.

This arguably rapid transformation within the legal landscape has risen in parallel with, and possibly in tandem to, changes in cultural attitudes towards cannabis use. The authors also noted a reduced perception of harm regarding the use of cannabis throughout the general public.

Additionally, in regards to increasing cannabis usage amongst youth, the authors noted this rise of cannabis consumption in parallel to the recent surge in vapor-based nicotine consumption, i.e., “vaping,” which has led to an increase in vaping devices, such as vape pens, which are easily concealable (and sometimes indistinguishable from electronic cigarettes) and can be used to consume cannabis. The stealthy nature of such devices may draw an appeal towards the younger demographic.1

Age of Cannabis Use and the Link to Psychosis

Cannabis contains two primary active chemical components: Delta-9-Tetrahydrocannabinol (THC) and cannabidiol (CBD). THC is the psychoactive chemical that produces intoxicating effects and is speculated to have a strong link to psychosis and schizophrenia. CBD, conversely, has been suggested to have antipsychotic effects.

The rapidly turning legal climate has given way to increased availability of cannabis products that have additionally been noted to contain significantly higher levels of THC than their predecessors of previous generations. THC is what directly correlates with potency, and the percentage of THC content in both illicit and commercial cannabis markets has increased from approximately 3.96% in 1995 to 11.84% in 2014.1 This increase in THC, notably, has not been matched with increases in CBD levels. CBD levels have remained stagnant throughout this same period, while THC content has markedly increased.

Cannabis use has been linked to those who have chronic schizophrenia and psychosis. Cannabis use after the first episode of psychosis has been associated with poor prognosis, worsening psychotic symptoms, and psychosocial functioning. The authors noted laboratory studies in which it was found that a single dose of THC caused psychotic symptoms in a greater proportion of those with schizophrenia as compared to those without. Consistent cannabis use after the first episode of schizophrenia is associated with a 2.2-fold increased risk in relapse (after controlling for confounding factors such as lack of medication adherence).1 It was also noted that discontinuation of cannabis use after the first episode of psychosis reduced the risk of experiencing further psychotic episodes with similar frequency to non-users of cannabis. Cannabis abstinence has been notably associated with the improvement of symptoms, functioning, and the probability of remission from psychosis.

Long before the authoring of this article, the adverse effects of using cannabis while recovering from a psychotic episode or disorder were already well established. This article highlighted new findings in research and literature that point towards a link between high-potency cannabis, early age of use, and high frequency of use to the earlier onset and unique course of psychosis and schizophrenia that we see today.

It was suggested that youth cannabis use has the potential to compromise early brain structure and function. Evidence of causal, rather than correlational nature, has pointed towards a strong dose-dependent relationship between cannabis use and psychotic disorders. This is further evidenced in data that suggests those who use cannabis frequently throughout a long duration of time are more likely to experience a psychotic episode than even those who consume on an intermittent or sporadic basis.

Late adolescence was highlighted as the particular period of development during which one is particularly susceptible to the detrimental effects of cannabis consumption in regards to psychosis. As pointed out by the authors, this is because during this period, in particular, the brain is remodeling extensively to process higher cognitive functioning through increasing the volume of its white matter. White matter is filled with cells that transmit information to each other. A greater volume of white matter, therefore, allows for the greater and more rapid flow of information throughout the brain.

As mentioned earlier, psychosis usually develops during this particular time, and, as it affects the white matter of the brain, it is consequently associated with impaired brain functioning. Cannabis use during this time can further compound these adverse effects on the brain, which can last for a very long time beyond adolescence and into adulthood. Evidence to support this came from the analysis of adult cannabis users, which displayed long-term (as well as immediate) negative effects on brain structure, connectivity, and function.

The authors highlighted a recent study that suggested youth who use cannabis with high THC content is three times more at risk of developing a psychotic disorder when compared to those who have never used cannabis.2 This same study suggested that daily users of high-THC cannabis displayed the highest risk of developing a psychotic disorder (when compared to other potential risks).

Another recent study highlighted by the authors had drawn conclusions which suggested that daily use of high-THC cannabis was associated with a five-fold increase in the risk of developing psychosis as compared to those who never use cannabis.3
This same study looked toward data that suggested that cannabis-users who develop schizophrenia are usually significantly younger than those who have never used cannabis.


Ultimately, psychosis and schizophrenia, in congruence with a litany of psychiatric/mood disorders, involves a cornucopia of potential instigating factors. This study did not take into account the potential power of other risk factors for psychosis/schizophrenia such as genetics, childhood trauma, urban living, and tobacco use.4,5,6

The article also mentioned an Australian study with conflicting findings to the trends noted by the authors. This study examined data collected throughout three decades in which there was no substantial link drawn between an increase in schizophrenia and increased cannabis use within this time.1

Final Thoughts

This journal article was admirably thorough in its research and presentation of the data studied. Although it can be inferred that abstaining from cannabis use is a highly effective way to reduce the probability of developing early-onset psychosis and reduce the risk of prolonging episodes of psychosis in those who already have schizophrenia, the study also makes a point to highlight how the origins of these conditions are multifactorial, and how these other factors, in congruence with cannabis use, were not entirely evaluated during this particular study. The subject appears to be rife with nuance, as mental disorders are very complicated issues that are still not yet fully understood. This is one study that brings us closer to that understanding. Only through further analysis of data and trends compiled from studies both past and present, can we begin to form a solid understanding of what affects the most important organ in the human body- that which holds the mind.


  1. Wright, Abigail, et al. “The Changing Legal Landscape of Cannabis Use and Its Role in Youth-Onset Psychosis.” Child and Adolescent Psychiatric Clinics of North America, vol. 29, no. 1, 1 Jan. 2020, pp. 145–156., doi:10.1016/j.chc.2019.08.016.
  2. Di Forti M, Marconi A, Carra E, et al. Proportion of patients in south London with first-episode psychosis attributable to use of high potency cannabis: a case- control study. Lancet Psychiatry 2015;2(3):233–8.
  3. Di Forti M, Quattrone D, Freeman TP, et al. The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multi- centre case-control study. Lancet Psychiatry 2019;6(5):427–36.
  4. Krabbendam L, Van Os J. Schizophrenia and urbanicity: a major environmental influence – conditional on genetic risk. Schizophr Bull 2005;31(4):795–9.
  5. Harley M, Kelleher I, Clarke M, et al. Cannabis use and childhood trauma interact additively to increase the risk of psychotic symptoms in adolescence. Psychol Med 2010;40(10):1627–34.
  6. Myles N, Newall H, Compton MT, et al. The age at onset of psychosis and tobacco use: a systematic meta-analysis. Soc Psychiatry Psychiatr Epidemiol 2012;47(8):1243–50.
  7. Ganti L, Kaufman MS, Blitzstein SM. First Aid for the Psychiatry Clerkship. McGraw Hill Professional; 2016: p. 26.
  8. Fischer BA, Buchanan RW. Schizophrenia in Adults: Clinical Manifestations, Course, Assessment, and Diagnosis. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. http://www.uptodate.com/contents/schizophrenia-in-adults-clinical-manifestations-course-assessment-and-diagnosis. Last updated February 27, 2017. Accessed May 15, 2017.
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