Cannabis is the most prevalently used federally illegal drug in the U.S, with roughly 18% of the population, equivalent to about 48.2 million people, reporting its usage, according the Centers for Disease Control and Prevention (CDC).
Nearly one-third of marijuana users are likely to develop a use disorder, with the odds significantly higher for those who began consumption before turning 18. The drug mainly impacts areas of the brain responsible for a range of functions, including memory, attention, decision-making, coordination, emotions, and reaction time. Furthermore, persistent or regular marijuana usage has been associated with an increased likelihood of psychosis or schizophrenia in certain users.
This association has been a fierce topic of debate in the medical field, but a new study from the University of Oslo published in the Lancet Psychiatry called “The relationship between cannabis use, schizophrenia, and bipolar disorder: a genetically informed study” has revealed shared genetics for cannabis use and psychiatric disorders.
The Research
The latest research spearheaded by Drs. Weiqiu Cheng and Nadine Parker suggests that the connection between cannabis use and the development of conditions like schizophrenia or bipolar disorder can be traced back to common genetic factors. Utilizing sophisticated statistical models, the study shows that a significant proportion of these shared genetic variants elevate the risk of both marijuana usage and the onset of either schizophrenia or bipolar disorder.
According to lead author, Dr. Cheng, “This study shows that there is a shared genetic basis underlying our susceptibility to both cannabis use and certain psychiatric disorders. These findings may indicate that a subset of the population is at high risk for both cannabis use and psychiatric disorders, based on their genetic propensity.”
The study’s methodology included:
- Utilizing genome-wide association summary data from individuals of European descent, sourced from the Psychiatric Genomics Consortium, the UK Biobank, and the International Cannabis Consortium.
- Estimating the heritability, polygenicity, and discoverability of each phenotype to assess their genetic influence and likelihood of being genetically mapped.
- Conducting both genome-wide and local genetic correlations to analyze the degree of genetic similarity between different traits.
- Identifying and mapping shared loci to specific genes
- Testing these specific genes for functional enrichment to investigate whether they have an unusually high amount of a particular trait.
- Exploring the shared genetic liabilities to psychotic disorders and cannabis-related traits using causal analyses and polygenic scores.
- Applying the findings to the Norwegian Thematically Organized Psychosis cohort
Clinical Implications
The study’s findings reveal:
- The new data could lead to tailored care, incorporating preventive strategies and interventions for those individuals at heightened risk. This could encompass efforts to decrease cannabis use among people with a high genetic predisposition for conditions such as schizophrenia and bipolar disorder.
- Upcoming research that delves into the biological impacts of these shared genetic variants might pave the way for the creation of more specific treatments.
- An enhanced understanding of the genetic overlap could be employed to categorize patients more accurately, facilitating the development of more personalized treatment plans.
As the rates of cannabis use continue to grow—in the context of the present day adolescent mental health crisis with historic rates of teen suicide—such research remains critical in refining our understanding of the impact of cannabis use among teens with different risk factors.
