Cannabis and Tobacco Co-Use Linked to Near-Threefold Psychosis Risk in At-Risk Youth
A multisite study of over 1,000 individuals at clinical high risk for psychosis finds that using cannabis and tobacco together markedly raises long-term risk of developing a full psychotic disorder—about 2.9 times higher than non-users—compared with single-substance use. The effect is partly biological, as smoking tobacco increases cannabis THC absorption, potentially accelerating brain changes. Short-term symptoms rise with either substance, but the major difference appears over time in conversion risk, especially for heavy cannabis use paired with light tobacco use. Stopping both substances could reduce risk, highlighting the need to address co-use in at-risk populations. For those with established psychosis, ongoing tobacco use is linked to a roughly 20-year decrease in life expectancy due to cardiovascular and respiratory diseases.
