Original article
What every adolescent needs to know: Cannabis can cause psychosis

https://doi.org/10.1016/j.jpsychores.2010.04.002Get rights and content

Abstract

Objective

Cannabis is a widely used substance that may be becoming more socially accepted, legally tolerated, and utilized by younger individuals. This review explores the relationship between cannabis and the onset of psychosis as well as the policy ramifications of current research.

Method

This article synthesizes published work that was considered by the author to be relevant to the discussion of cannabis and the onset of psychosis.

Results

The evidence suggests that, along with other harms, cannabis is a significant risk factor in the etiology of psychosis. Adolescents are more vulnerable to using cannabis, and because of their stage of mental development, the cognitive effects are more pronounced. The mechanism for this change is thought to be neuro-chemical with a stronger effect in those with a diathesis for psychosis.

Conclusion

The risk that cannabis poses to adolescent health should not be neglected. Policy measures should use a multifaceted and strategic perspective in order to prevent adolescents from using this drug.

Introduction

Cannabis use and acceptance have increased among adolescents worldwide [1]. Currently, cannabis is the most widely used illicit drug in most English-speaking countries such as Canada, New Zealand, Australia, and the United States [2]. Despite being an illicit drug in Canada, one in seven adults and one in four students reportedly use cannabis [3]. There are reports of an even higher prevalence of cannabis use in students (one in three) [4]. A recent survey of middle and high school students in Nova Scotia found cannabis to be more widely utilized than cigarettes, and while 16.2% of adolescents used cigarettes, 32.4% used cannabis in 2007 [5]. Furthermore, in a study carried out in New Zealand it was shown that almost 70% of a 21-year-old cohort population used cannabis [6]. Cannabis use is even more striking in certain demographic groups. For example, in one survey 92% of street youth report using cannabis ‘in the past year’ and 16% report ‘daily use’ [7]. Adolescents appear to be at a double disadvantage as they are more vulnerable to using cannabis [8] and the effects of cannabis on cognitive measures are more pronounced in adolescence [9], [10].

In 1991, Boyle and Offord [11] wrote, “Despite the many studies that have reported associations between maladjustment and substance use in adolescence, we know little about the relationship between adolescents substance abuse and specific types of psychiatric disorders.” Other articles have made light of cannabis use, one calling it “safer than aspirin” [12]. However, with such a high prevalence of adolescents using cannabis it is imperative to firmly conclude whether the result of this action causes psychosis. At this point in time there are strikingly contradictory views regarding the possible neurobiological role of cannabis in triggering long-term psychosis, with some viewing the likelihood of long-term brain effects as unlikely [13] and others arguing that a lasting effect is likely [14]. This article will review the relationship of cannabis and psychosis as well as discuss the policy implications of these findings.

Section snippets

Background

Cannabis refers to marijuana and other preparations made from the hemp plant Cannabis sativa. The active ingredient in Cannabis is primarily Δ-9-tetrahydrocannabinol (THC), although there are over 60 other related compounds. All these forms act as agonists at the CB1 receptor [15]. If THC is taken orally, it will take 1–3 h for the drug to have an effect; however, if inhaled, it reaches the brain tissue within minutes. Users typically feel light-headed, calm, drowsy, a subjectively sharpened

Cannabis use and schizophrenic symptoms

There is controversy in the literature over whether cannabis causes psychosis. In Kendell's 2003 article [27] entitled “Cannabis Condemned: The Proscription of Indian Hemp,” he describes how cannabis historically gained a reputation as a drug of addiction based on politics, not on medical evidence. Although Kendell [27] acknowledges that cannabis can lead to acute psychotic episodes, his review did not find sufficient evidence to infer a causal relationship with chronic psychosis. Kendell [27]

Other notable effects of cannabis

Cannabis use is related to emotional distress, depression, and lack of a sense of purpose [54]. In addition, cannabis can interfere with learning and personal development in teenagers. Short-term memory is impaired by the use of cannabis [55] and in particular the impact on cognitive function is more severe in younger users [9], [10]. This result is contradicted by Müller-Vahl et al. [56] who investigated the cognitive effects of THC over a 6-week period and did not observe any differences on

Policy implications

It is becoming increasingly accepted that cannabis use is harmful to adolescents especially with early, frequent, and chronic use [62]. The recent plethora of evidence suggesting that cannabis is a causative agent in the development of schizophrenia/chronic psychosis adds to a multiplicity of other documented adverse health consequences. The logical conclusion is that it would be sensible to pursue policies that will reduce the use of cannabis amongst adolescents.

The negative health

Conclusion

Although there has been a long history of suggestion that cannabis consumption may be a causative agent in the development of schizophrenia, the influential review by Kendell [27] in 2003 seemed to negate this notion or at the very least indicate that there was insufficient evidence to come to this conclusion. It is therefore remarkable that in the last few years there have been a plethora of studies all pointing to an increased risk of schizophrenia/chronic psychosis when adolescents use

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