Psychosis is a broad term that describes a change in the perception of reality. It can be caused by various conditions, including metabolic, psychiatric, neurologic, genetic, and other medical conditions, as well as licit and illicit substances, particularly cannabis. The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) states that abnormalities define these disorders in one or more of the following five domains: delusions, hallucinations, disorganized thinking (speech), grossly disorganized or abnormal motor behavior (including catatonia), and negative symptoms.
Cannabis-induced psychosis has been subject to debate but is becoming more prevalent in areas where use rates are increasing. This increase may be related to improved diagnostic evaluation, medical coding, increased understanding of the condition, and increased cannabis potency. Studies have shown a 3-fold increased risk of psychosis with “skunk,” which is generally accepted as cannabis with more than 10 percent tetrahydrocannabinol (THC) content.
Violence associated with psychosis has also been well-documented. Marijuana use may be associated with increased impulsivity on the same day and the following day relative to days when marijuana was not used. It is also associated with increased hostile behaviors and perceptions of hostility in others on the same day compared to days when marijuana was not used. Cannabis use disorder appears to increase the risk of aggression towards others, particularly among youths. There is also evidence of a moderate association between cannabis use and physical violence.
Psychosis can be caused by various conditions, including licit and illicit substances, particularly cannabis. Cannabis has a higher conversion rate to psychosis than other substances. 32 percent of patients with substance-induced psychosis convert to either bipolar or schizophrenia-spectrum disorders, with the highest conversion rate found with cannabis-induced psychosis (47 percent). There is debate about the causal relationship between cannabis and psychosis. However, this can be demonstrated using Bradford-Hill criteria. Despite this, psychosis is often multifactorial in many instances. Cannabis exposure increases the risk of psychosis, from transient psychotic states to chronic recurrent psychosis. In individuals with established psychosis, cannabis has a negative impact on the course and expression of the illness.
Individuals who use cannabis frequently are at an increased risk of psychosis, with no significant risk associated with less frequent use. There is a significant dose-response association between cannabis use frequency and psychosis development. Frequently overlooked is the fact that psychosis precipitated by cannabis use may persist, despite cessation, and may not resolve. Recent data shows that hospitalizations for psychosis/cannabis use are more likely in areas where cannabis is legalized, and recreational cannabis legalization is associated with a greater rate of hospitalization for psychosis associated with cannabis use.
Several likely factors contribute to the trend of cannabis-induced psychosis, including increased normalization of cannabis use, decreased perception of harm, rapid development of higher potency products in recent years, and products with less cannabidiol, which has been shown to have a potential protective effect. Furthermore, progression to schizophrenia is highest in those with cannabis-induced psychotic disorder and is predicted by early age at diagnosis of substance-induced psychotic disorder, male sex, and other episodes of drug abuse, alcohol use disorder, and substance-induced psychotic disorder.
Adolescents who use cannabis report more psychotic-like symptoms than controls and more than adults, independent of depression and anxiety. Delaying onset of use, discouraging the use of products with greater than 10 percent THC content and preventing daily or near-daily use should be part of the educational process, starting at early ages. Potency caps should be mandated as “high potency” cannabis should be considered in any product with greater than 10 percent THC due to a 5-fold risk of developing psychosis, according to more recent data.
It would be critical that areas expanding cannabis programs seriously consider mandatory drug testing on any violent crime, including mass shootings, which are becoming more prevalent, and make those findings public. Public health campaigns, underscoring the health risks of cannabis, including psychosis, should be strongly encouraged and disseminated to the medical community, general public, and state legislators to allow for better-informed policy development. Consistency in testing is strongly recommended. The potential relationship between cannabis use and psychosis cannot be ignored.
Ken Finn is a physiatrist.