Cannabis, also known as marijuana or weed, is now used by millions of people around the world—both for medical reasons and recreational enjoyment.
In recent years, its use has been fully legalized or decriminalized in several countries, including Canada, Germany, Spain, Portugal, and many U.S. states. While many people use cannabis without any problems, others develop issues such as dependency or mental health struggles.
Scientists have long been debating whether cannabis use can actually cause psychiatric disorders, especially when the drug is used heavily or abused. Some studies suggest cannabis has medical benefits, particularly due to cannabidiol (CBD), the non-psychoactive ingredient in the plant.
But other studies point to problems linked to tetrahydrocannabinol (THC), the compound that causes a high. High-THC use, especially in large amounts or over time, has been linked to serious mental health concerns, including anxiety, depression, and even psychosis.
Now, researchers from Yale University, Washington University, and the Veterans Affairs Connecticut Healthcare System have uncovered new genetic evidence linking cannabis use disorder (CanUD) with a range of psychiatric illnesses. Their study, published in Nature Mental Health, looked at the complex genetics behind cannabis use and mental health.
Cannabis use disorder is a condition where someone struggles to stop using cannabis, continues using it despite negative consequences, and finds that it interferes with daily life. It’s different from casual use because it involves a loss of control and signs of addiction.
To explore the connection between cannabis use, CanUD, and mental health conditions, the researchers analyzed massive amounts of existing genetic and psychological data. They used advanced tools like genomic structural equation modeling, colocalization analysis, and Mendelian randomization.
These methods helped them not only look at genetic patterns, but also understand whether one condition might actually cause the other due to shared genes.
Their findings were eye-opening. First, they discovered that cannabis use and cannabis use disorder are not genetically the same. Just because someone uses cannabis does not mean they are at risk of mental illness.
However, those with CanUD showed much stronger and more consistent genetic links to psychiatric disorders—including schizophrenia, depression, bipolar disorder, and ADHD.
One genetic variant, related to a gene called CHRNA2, was found to be shared by both CanUD and schizophrenia. This gene is known to play a role in how the brain processes dopamine, a chemical linked to pleasure and reward. CHRNA2 has also been tied to nicotine use, another addictive behavior.
The team also found that cannabis use disorder and psychiatric disorders had a two-way relationship. This means that heavy cannabis use might raise the risk of developing a mental illness, but people who already have a mental illness may also be more likely to develop a cannabis use disorder. This two-way link was especially clear for conditions like ADHD and major depression.
Interestingly, these strong links were not found for casual cannabis use. In other words, someone who occasionally uses cannabis recreationally may not have the same level of risk as someone with a full-blown use disorder. This highlights the importance of distinguishing between moderate use and addiction when studying cannabis and mental health.
The researchers say their findings could help guide public health strategies. For example, identifying people with certain genetic risks could allow for earlier monitoring or interventions to prevent the development of cannabis use disorder.
It could also lead to better education around the risks of cannabis abuse, especially in those already dealing with psychiatric symptoms.
In conclusion, while cannabis may offer medical benefits for some, this study adds to growing evidence that abuse of the drug—especially when it becomes a disorder—is linked to serious mental health conditions.
The genetic connections uncovered in this research may help doctors, scientists, and policymakers better understand who is at risk and how to protect mental health in the era of increasing cannabis use.
If you care about mental health, please read studies about how dairy foods may influence depression risk, and 6 foods you can eat to improve mental health.
For more mental health information, please see recent studies about top foods to tame your stress, and Omega-3 fats may help reduce depression.
The research findings can be found in Nature Mental Health.
Copyright © 2025 Knowridge Science Report. All rights reserved.
