Scientists Warn That Using Cannabis and Tobacco Together May Greatly Increase Psychosis Risk
Cannabis and tobacco are two of the most commonly used substances around the world.
In recent years, cannabis use has increased in many places as laws have changed, while cigarette smoking has gradually declined. At the same time, more people are using both cannabis and tobacco together.
Doctors have been concerned that this combination may have stronger effects on the brain than either substance alone, especially in young people and those already at risk of mental illness.
Psychosis is a serious mental health condition that affects the way a person thinks and understands reality.
People may experience hallucinations, false beliefs called delusions, confused thinking, or difficulty telling what is real.
Schizophrenia is one of the best-known psychotic disorders. Scientists know that genes, brain development, life experiences, and substance use can all influence a person’s risk.
A new multisite study led by researchers at Vanderbilt University Medical Center examined whether cannabis and tobacco use affected people who were already considered to be at high risk of developing psychosis.
The researchers analyzed information from more than 1,000 participants in the North American Prodrome Longitudinal Study. These individuals had early warning signs of psychosis but had not yet developed a full psychotic disorder.
Participants were followed for two years. The researchers compared people who used only tobacco, only cannabis, both substances, other drugs, or no substances at all.
The study found that regular use of either cannabis or tobacco was linked to higher levels of anxiety, depression, and early psychotic symptoms.
However, the most important finding appeared during long-term follow-up. People who heavily used cannabis while also using tobacco were nearly three times more likely to develop psychosis than people who used neither substance.
Researchers believe using both substances together may increase the amount of THC absorbed by the body. THC is the main chemical in cannabis that affects the brain. This may partly explain why using both substances together could have stronger effects than using either one alone.
The researchers say more studies are needed, but the findings suggest that avoiding both cannabis and tobacco may be especially important for people already at risk of schizophrenia and related disorders.
The study was published in Nature Mental Health.
Overall, this research provides important evidence that using cannabis and tobacco together may increase the risk of developing psychosis in people who are already vulnerable. Because the study followed more than 1,000 participants over time, it is stronger than studies that only look at one point in time. However, it cannot prove that cannabis and tobacco directly cause psychosis.
Other genetic, environmental, or mental health factors may also contribute. The findings suggest that doctors should routinely ask high-risk patients about both cannabis and tobacco use and provide support to help them quit.
Future studies will need to determine whether stopping both substances can actually reduce the risk of schizophrenia and other psychotic disorders.
If you care about mental health, please read studies about 6 foods you can eat to improve mental health, and B vitamins could help prevent depression and anxiety.
For more health information, please see recent studies about how dairy foods may influence depression risk, and results showing Omega-3 fats may help reduce depression.
