What the Research Found

A new study has shed important light on how cannabis and tobacco co use affects young people already at clinical high risk for psychosis (CHR-P). Published in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, this is the first investigation of its kind. The findings carry real implications for adolescent mental health.

Researchers drew on data from 1,012 participants in the North American Prodrome Longitudinal Study 2 (NAPLS2). This multisite study spans eight sites across North America. Of the total participants, 734 were at clinical high risk for psychosis and 278 were healthy controls. Each participant completed a broad neuropsychological test battery, including the MATRICS Consensus Cognitive Battery and the Seidman Auditory Continuous Performance Task.

The results tell a clear story. At-risk individuals who used both cannabis and tobacco scored significantly lower on global cognitive performance than healthy controls. Working memory, verbal learning, and attentional performance all showed notable impairments. These effects appeared even with light to moderate levels of use.

Why Cannabis and Tobacco Co Use Is a Growing Concern

Cannabis and tobacco co use has been rising steadily for decades. Among young people aged 18 to 25 in the United States, one in five daily cigarette smokers also uses cannabis daily. By 2014, daily cannabis use among cigarette smokers had doubled, climbing from 4.9% in 2002 to 9%.

Co-use takes many forms. Some people use both substances at the same time, for example through spliffs combining cannabis and loose-leaf tobacco. Others use them separately at different points in the day. Either way, the developing brain faces a heavier burden than it would from either substance alone.

In the general population, co-use of cannabis and tobacco already raises the risk of mental health disorders. For young people showing early warning signs of psychosis, that risk becomes far more serious.

Cannabis and Tobacco Co Use and Cognitive Risk in Vulnerable Young People

One of the more revealing aspects of the study involves the cannabis-only group. Unlike every other CHR-P group, those who used only cannabis did not show significantly lower global cognitive performance than healthy controls. Their IQ scores also held close to the healthy control range. Higher cannabis use frequency even correlated with better working memory performance among CHR-P individuals.

This pattern helps explain something that has long puzzled the field. Research on cannabis use and cognition in early psychosis has produced inconsistent findings for years. Some studies report better cognitive performance in cannabis users, others find no difference at all. This new study points to a likely explanation. Earlier studies may not have separated co-users from those using cannabis alone. When researchers isolate cannabis and tobacco co use, a more concerning picture emerges.

Tobacco use, whether alone or alongside cannabis, linked to lower cognitive performance across the board. Researchers suggest this may reflect self-selection rather than direct harm. People who gravitate towards tobacco may already carry underlying cognitive vulnerabilities. Nicotine may temporarily sharpen their performance, but the pattern of use still signals greater underlying risk.

The Surprising Finding About Non-Substance Users

The most unexpected result involved the group that used no substances at all. These at-risk young people also scored poorly on cognitive tests. They also showed the lowest social functioning of any CHR-P group in the study.

Researchers offer a straightforward explanation. Adolescent substance use is strongly tied to social engagement. Young people who withdraw socially, perhaps because of more severe negative symptoms, simply have fewer chances to encounter substance use in the first place. This means the non-substance-using group may already represent a more severely impaired subtype, not a protected one.

Co-investigator Ricardo E Carrión, PhD noted that at-risk individuals who avoid all substances may represent a distinct, socially impaired subtype. Because substance use among adolescents often happens through social interactions, those who are less social may have fewer opportunities to engage with it.

What This Means for Young People

Cognitive impairment ranks among the earliest warning signs of psychosis risk. The prodrome, the window before definitive psychotic symptoms emerge, is also when young people typically begin experimenting with substances. This overlap makes it a critical period.

Cannabis and tobacco co use appears to signal a more serious neurocognitive risk profile than either substance on its own. Earlier research from the same group found that co-users faced a threefold increased risk of converting to full psychosis compared to those using cannabis alone. The cognitive impairments found here may help explain why. Working memory and vigilance, two of the domains most affected by co-use, play a central role in how young people function, learn, and connect socially during adolescence.

The co-use of cannabis and tobacco therefore deserves attention as a distinct risk factor, not just a variation on single-substance use.

Limitations and the Road Ahead

The study relied on self-reported substance use covering the past 30 days. Researchers had no detailed data on dosage, duration, cannabis potency, or alternative nicotine products like vaping. Testing also happened at a single point in time, so it remains unclear whether cannabis and tobacco co use causes cognitive decline or whether at-risk individuals with existing vulnerabilities are more drawn to co-use in the first place.

Longitudinal research will be essential. Tracking cognitive performance over time, alongside frequency of cannabis and tobacco co use, will help clarify the direction of these effects.

What this study makes clear right now is that co-use of cannabis and tobacco carries meaningful cognitive risks for young people at clinical high risk for psychosis, and those risks appear even at low levels of use.

Source: dbrecoveryresources