A major longitudinal study has tracked the substance use habits of tens of thousands of Americans. It reveals a complicated and shifting picture of how young people combine nicotine, alcohol, and cannabis. The findings come from the Population Assessment of Tobacco and Health (PATH) Study, covering three waves of data collected between December 2016 and November 2021. They paint a telling portrait of substance co-use among youth and adults that policymakers, educators, and health services cannot ignore.

What the Research Examined

Researchers at Brown University’s School of Public Health published this study in Addictive Behaviors in 2026. They analysed data from over 41,000 participants aged 15 and above in Wave 4, with follow-up in Waves 5 and 6. The team tracked past 30-day co-use of cigarettes, e-cigarettes, and other tobacco products (OTP) such as cigars, hookah, and smokeless tobacco, alongside alcohol and cannabis.

The scale of the study makes its findings particularly significant. The research uses nationally representative cohort weights. This gives it some of the clearest population-level insights yet into tobacco and alcohol co-use trends across age groups in the United States.

Substance Co-Use Among Youth: E-Cigarettes and Alcohol Lead the Way

E-cigarettes combined with alcohol stood out as the most striking finding for younger age groups. For young people aged 15 to 17, this was the most common co-use pattern across the entire study period. Rates rose initially before declining, suggesting the early peak of vaping among teenagers had begun to plateau by 2021.

Among adults aged 18 to 24, e-cigarette and alcohol co-use jumped sharply at Wave 5 (OR = 1.94). Researchers suggest e-cigarettes may be supplanting traditional cigarettes in social settings where alcohol is present. This matters greatly for understanding substance co-use among youth and young adults. The health risks of combining vaping with alcohol are still emerging, but the evidence so far is concerning.

Adults aged 35 to 64 showed only a modest rise at Wave 5. Older adults aged 65 and above remained broadly stable throughout.

Tobacco and Alcohol Co-Use Trends: Cigarettes in Decline

Traditional cigarette and alcohol co-use told a different story. This combination remained the most prevalent form across all adult age groups, but it fell meaningfully among younger cohorts over time.

Among adults aged 18 to 24, the odds of cigarette and alcohol co-use dropped at Wave 5 (OR = 0.70) and kept falling into Wave 6 (OR = 0.48). Adults aged 25 to 34 showed similar declines. For older adults aged 65 and above, the pattern barely shifted. This is a concern in itself. This group is less likely to attempt quitting and more vulnerable to long-term health consequences from combined tobacco and alcohol use.

The shift in tobacco and alcohol co-use trends shows how quickly habits can change. It also shows why a single approach to prevention rarely works across all age groups.

Cannabis Co-Use Among Youth and Adults: A Shifting Picture

The relationship between nicotine products and cannabis proved to be one of the most dynamic areas of the study. E-cigarette and cannabis co-use rose across all age groups between Waves 4 and 5. Among those aged 15 to 17, the odds nearly doubled (OR = 1.92 at Wave 5). Adults aged 25 to 34 saw that rise continue into Wave 6 (OR = 1.98), even as rates levelled off slightly for younger groups.

Cigarette and cannabis co-use, by contrast, fell sharply among younger participants. Youth aged 15 to 17 saw the odds drop by 61% between Waves 4 and 6. Adults aged 18 to 24 saw similar reductions. These declines likely reflect the broader fall in cigarette use rather than a deliberate move away from combining the two substances.

For older adults aged 65 and above, cigarette and cannabis co-use was low but rising. By Wave 6, the odds had more than doubled from baseline (OR = 2.03). Researchers rarely focus on this age group in substance use studies, which makes this trend easy to miss and harder to address.

Why Substance Co-Use Among Youth Carries Serious Health Risks

The health consequences of substance co-use among youth are well documented. Combining nicotine products with cannabis links to poorer smoking cessation outcomes, heavier cannabis use, and a far higher risk of nicotine dependence. Adolescents who co-used were 3.5 times more likely to become dependent on nicotine than those who did not.

Adding alcohol raises the stakes further. Cigarette smoking and heavy drinking reinforce each other at a physiological level, raising cravings and driving up consumption of both. Long-term co-use also creates compounding risks for aerodigestive tract cancers, cardiovascular disease, and mental health disorders.

What makes tobacco and alcohol co-use trends harder to address is the rapid change in the products themselves. E-cigarettes barely existed a decade ago. Now they sit at the centre of how young people access nicotine and, increasingly, cannabis.

What This Means for Prevention and Support

The study’s authors argue that responses must match the age group. Adolescents aged 15 to 17 and young adults aged 18 to 24 showed the highest rates of e-cigarette co-use with both alcohol and cannabis. Effective cessation tools for e-cigarettes are still limited. There is a real and urgent need for targeted interventions built for these groups, delivered in ways that actually reach them.

For teenagers, family-based approaches and digital tools have shown the most promise. For young adults, peer-led community models tend to land better. In both cases, substance co-use among youth needs treating as its own distinct challenge, separate from single-substance use, with different motivations, patterns, and risks.

Older adults should not fall off the radar either. Their co-use rates were lower but often stable or creeping upward. They also face greater health risks and are statistically less motivated to seek help.

A Baseline the Field Cannot Afford to Ignore

Research like this matters most as a benchmark. The tobacco and alcohol co-use trends captured here cover five years of rapid change. That window included the vaping surge, cannabis legalisation across multiple US states, and major social disruptions that reshaped everyday behaviour.

What happens next will depend on oral nicotine products such as pouches, expanding cannabis markets, and whether public health systems act on what the data already shows.

The numbers are clear. Whether the response matches the challenge is another question entirely.

Source: sciencedirect