Researchers had subjects complete self-assessments regarding drug use and psychosis spectrum symptoms to determine a relationship between marijuana use and psychosis. They found that there was no significant increase in the risk of psychosis spectrum symptoms in subjects that only used marijuana; however, subjects that combined marijuana with other drugs were at a significantly higher risk of developing psychosis symptoms.
Marijuana is currently a subject of hot debate as more states begin to legalize its recreational use. Among the youth population of the United States, marijuana is the most commonly used illegal drug, and attitudes about marijuana are shifting towards it being of little harm. In fact, social media is littered with claims of marijuana’s medicinal properties with little scientific evidence backing such broad statements. Researchers continue to be highly interested in the effects that cannabis use may have on mental health, particularly in the developing minds of adolescents and young adults.
Various studies have suggested that cannabis use is associated with symptoms of psychosis, including both positive symptoms–hallucinations, paranoia, and delusions–and negative symptoms–lack of emotion and inability to experience pleasure. These studies have also suggested that cannabis use correlates to the development of psychotic disorders later in life. However, the vast majority of these studies have not taken into account the fact that a large portion (up to 29%) of cannabis users also indulge in other illicit substances, and the studies that did evaluate polysubstance abuse showed a markedly decreased association between marijuana use and the development of psychotic disorders in users that only used marijuana.
In a study recently published in the Journal of Adolescent Health, researchers at the University of Pennsylvania School of Medicine utilized data from the Philadelphia Neurodevelopmental Cohort (PNC) to examine the relationship between cannabis use, alone and with other substances, and psychotic disorders. The PNC consists of 9,498 youths between 8- and 21-years-old from the greater Philadelphia area. Researchers excluded patients less than 14-years-old; 5 patients were excluded due to missing data, and 32 were excluded for “endorsing fake drugs”. The resulting population was 4,171 patients with a mean (SD) age of 16.9 years (1.85).
Based on self-assessment, patient’s marijuana use was categorized as frequent, occasional, or nonuser. Psychotic symptoms, psychotic diagnoses, trauma exposure, intellectual function, and a family history of substance abuse were assessed using computerized screening tools.
After adjusting for confounding factors, researchers found no significant increase in the odds of developing psychotic symptoms in individuals using only marijuana. However, they did find that marijuana combined with tobacco or other illicit drug use did significantly increase the risk of developing psychotic symptoms. More specifically, cannabis use with other illicit drugs produced significantly higher odds of developing positive symptoms. Frequent marijuana users had higher odds of developing negative symptoms. No group had significantly increased odds of developing delusions or hallucinations.
A few limitations of this study included the brevity of patient assessments and the age of the PNC cohort. Because patients were relatively young, it is possible that psychotic disorders had not yet manifested. Also, researchers did not take into account the possibility that patients could have been acutely intoxicated during assessments.
Studies evaluating the effects of marijuana in the general US population are lacking and more studies are needed to evaluate the effects that marijuana use has on the developing mind. Researchers hope that the results of this study implore the continuing investigation of combined drug use and the development of psychotic disorders.
Written By: Corey Cunningham, PharmD