Teenage brain tangled with marijuana and alcohol

Weed and Alcohol: Unraveling the Impact on Adolescent Brains

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Rhea Morgan in Health & Wellness November 2026 • 4 min read.

"A deep dive into how combining cannabis and alcohol affects teenage ingestive behaviors, cognitive functions, and overall health"


The co-use of alcohol and marijuana is a prevalent and growing trend, particularly among adolescents and young adults. While both substances are often used recreationally, the combined effects on the developing brain remain largely unexplored. Understanding how these substances interact is crucial, especially given the unique vulnerabilities of the adolescent brain.

A new study investigates the combined effects of alcohol and Δ9-tetrahydrocannabinol (THC), the main psychoactive component of marijuana, on ingestive behaviors and cognitive functions in adolescent male rats. By examining how these substances interact, the research aims to shed light on the potential consequences of co-use during this critical developmental period.

This article breaks down the key findings of the study, translating complex research into accessible insights. From appetite and weight changes to impacts on memory and learning, we’ll explore the surprising ways alcohol and THC interact and what these findings could mean for adolescent health.

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A Developing Public-Health Concern

Alcohol and cannabis can affect adolescents differently, and using them together may create additional concerns. The extent of their combined effects on the developing brain remains an active area of research. Because patterns of use, potency, age of initiation, and individual vulnerability vary, broad conclusions should be interpreted cautiously.

Measuring Co-Use and Its Limits

Research commonly distinguishes marijuana-only use, alcohol-only use, concurrent use, and simultaneous alcohol and marijuana (SAM) use. Studies have compared co-users with marijuana-only users while examining contextual factors such as environment and method of use. Longitudinal researchers may use latent curve models, growth mixture modelling, or latent class growth analysis, but selecting among these approaches requires careful judgment. Measuring cannabis exposure also remains difficult because the weight of dried plant material does not equal the dose of tetrahydrocannabinol or cannabidiol consumed.

An Evolving Research Tradition

Research on alcohol and cannabis has gradually moved from studying each substance separately toward examining dual and simultaneous use. This shift reflects growing interest in how patterns of use and social context shape outcomes. The historical record is still developing, and comparisons across periods are complicated by changing products, policies, and measurement methods.

How Do Alcohol and THC Affect Appetite and Weight?

Teenage brain tangled with marijuana and alcohol

The study reveals that the route of THC administration—whether through injection or ingestion—significantly influences its effects. Subcutaneous THC injections increased short-term food intake but reduced overall weight gain. Interestingly, moderate alcohol consumption seemed to lessen the acute hyperphagic (overeating) effect of THC. Oral THC, on the other hand, robustly reduced alcohol intake without affecting short-term food consumption. At higher doses, some rats even stopped consuming THC-laced cookies.

One of the intriguing findings was the interaction between alcohol and THC on weight gain. While oral THC reduced weight gain, co-exposure to alcohol seemed to alleviate this effect, suggesting a complex interplay between the two substances on energy balance.

Here are the key findings:
  • Subcutaneous THC increased short-term food intake and reduced weight gain.
  • Moderate alcohol consumption reduced the hyperphagic effect of injected THC.
  • Oral THC reduced alcohol intake, especially at higher doses.
  • Alcohol alleviated the weight-reducing effect of oral THC.
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Recent Evidence on Changing Use

Recent research has examined how daily or near-daily alcohol and cannabis use patterns are changing across developmental periods of adulthood in the United States. A 2024 narrative review drew on qualitative research, laboratory experiments, and naturalistic studies to examine the subjective effects of simultaneous alcohol and cannabis use. A 2025 cross-sectional study analyzed 4.8 million adults from the 2012–2022 Behavioral Risk Factor Surveillance System to assess how recreational cannabis laws relate to alcohol and tobacco use. Separate reporting has described possible substitution of cannabis for alcohol, but that finding should not be treated as resolving the broader evidence.

Why Simple Substitution Claims Fail

The evidence does not establish a single relationship between alcohol and cannabis: marijuana may substitute for alcohol for some people, while co-use may complement or increase alcohol use for others. Reviews emphasize the need to examine effects on alcohol and cannabis use patterns, alcohol use disorder and cannabis use disorder severity, and related problems. Research on adolescents has specifically investigated the contexts in which simultaneous use occurs and its effects on problems. These findings make broad claims that cannabis either universally replaces or universally worsens alcohol use incomplete.

No Simple Winner

Consumer health sources commonly describe cannabis as having fewer known risks than alcohol, while also noting that cannabis has not been studied as extensively. Healthline summarizes the comparison as having no easy answer: cannabis may appear safer, but there is not enough evidence to declare a definitive winner. Comparisons involve addiction, toxicity, brain effects, driving risk, mental health, and broader public-health impact. These uncertainties are especially important when discussing adolescents rather than adults.

These findings highlight that the combined use of alcohol and THC can lead to unique and sometimes opposing outcomes on ingestive behaviors and energy balance. This emphasizes the importance of considering both substances when assessing the potential health impacts on adolescents.

Why Does This Research Matter?

This research provides critical insights into how alcohol and THC interact in the developing brain, underscoring the potential for unique and sometimes counterintuitive outcomes on ingestive behaviors and energy balance. By establishing a novel model for studying voluntary alcohol and THC consumption, this study paves the way for deeper investigations into the mechanisms underlying adolescent substance use and its long-term consequences. Understanding these interactions is essential for informing public health strategies and interventions aimed at promoting adolescent health and well-being.

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Comparing Risks Carefully

Expert analysis questions whether cannabis should be regulated like alcohol solely because both substances can produce adverse health effects. One review critically examined the evidence behind that regulatory comparison and assessed what is known about the harms associated with each substance. Public perceptions do not necessarily match the research: a 2024 American Addiction Centers survey of more than 1,000 people examined which substance respondents considered more dangerous and whether either substance's legal status should change.

Tracking a Changing Market

Forecasts and industry reporting point to rapidly changing relationships between alcohol and cannabis markets. One 2026 market report claimed that alcohol consumption had reached a 90-year low while daily cannabis use exceeded daily alcohol use, and that cannabis tax revenues were two to seven times higher than alcohol taxes in mature legalization states. Another forecast reported a 40% increase in cannabis-alcohol sales in states with legalized cannabis, while coverage of 2025 trends highlighted growing interest in low-dose beverages. These figures come from market-oriented sources and should be treated as projections or reported claims rather than settled evidence about adolescent behavior.

Policy and Prevention Challenges

Alcohol and cannabis use are shaped by changing laws, product availability, social settings, and public perceptions. These influences can complicate prevention efforts, particularly when legal status and perceived risk do not move together. A broader response therefore requires careful measurement, age-appropriate education, and continued research rather than assuming that one substance is uniformly safer in every context.

Co-Use and Driving Risk

Researchers have examined the individual and joint effects of marijuana and alcohol on fatal motor-vehicle crash risk because concurrent use among drivers is an increasing concern. A newer study used a large-scale naturalistic driving dataset to investigate driving behavior after recent alcohol, cannabis, or combined-substance use and to inform detection and safety interventions. Reporting on that study described contradictory effects of cannabis and alcohol on real-world driving performance. Together, these sources support treating combined use as a practical road-safety issue while recognizing that its precise contribution to crashes remains under investigation.

Working memory compared with adolescents who did not use either substance

  • 2,216 adolescentsIMAGEN enrolled 2,216 adolescents at age 14 across eight sites.[1]
  • 3,826 studentsThe Montreal project assessed 3,826 seventh-grade students annually over four years.[2]

How adolescent cognition has been assessed

IMAGEN is a multicenter brain-imaging project that recruited adolescents from sites in Germany, the United Kingdom, and France.[1]

The Montreal assessment followed students through school-based computerized tests of recall memory, perceptual reasoning, inhibition, and working memory, alongside substance-use measures.[2]

What remains unresolved about brain effects

  • How much of a long-term brain difference is attributable to cannabis rather than genetics, the home environment, or other unknown influences?[3]
  • How do the reported cognitive differences relate to the continuing development of the adolescent brain, and do they persist as development proceeds?[3] [4]

Sources

  1. Alcohol and Cannabis Use and the Developing Brain (pmc.ncbi.nlm.nih.gov)
  2. A Population-Based Analysis of the Relationship Between Substance Use and Adolescent Cognitive Development. (pubmed.ncbi.nlm.nih.gov)
  3. Cannabis and Brain Health | Cannabis and Public Health | CDC (www.cdc.gov)
  4. Heavy alcohol use, marijuana use, and concomitant use by adolescents are associated with unique and shared cognitive decrements. (pubmed.ncbi.nlm.nih.gov)

About this Article -

Written with AI assistance from published research, and reviewed by the Mystum team. See our About page for more information.

Everything You Need To Know

1

How does the method of THC consumption (injection vs. oral) affect appetite and weight, and how does alcohol play a role?

Research indicates that when THC is administered through subcutaneous injections, it tends to increase short-term food intake but reduce overall weight gain. Conversely, moderate alcohol consumption appears to lessen the hyperphagic effect, or overeating, induced by THC. When THC is taken orally, it generally reduces alcohol intake. At higher doses, rats even stopped consuming THC-laced cookies. This highlights the complexity of how combined alcohol and THC use can lead to conflicting outcomes on ingestive behaviors and energy balance.

2

How does alcohol affect the weight-reducing effect of oral THC, and what does this suggest about energy balance?

The study found that oral THC reduced weight gain in adolescent male rats. However, co-exposure to alcohol seemed to alleviate this effect. This suggests a complex interplay between alcohol and THC on energy balance and body weight regulation. Further studies are needed to fully understand the mechanisms behind this interaction.

3

Why is it important to research the combined effects of alcohol and THC on adolescent brains?

This research is crucial because it provides valuable insights into how alcohol and THC interact in the developing brain. It highlights the potential for unique and sometimes counterintuitive outcomes on ingestive behaviors and energy balance. The study establishes a novel model for studying voluntary alcohol and THC consumption, which paves the way for deeper investigations into the mechanisms underlying adolescent substance use and its long-term consequences. Understanding these interactions is essential for informing public health strategies and interventions aimed at promoting adolescent health and well-being.

4

While the study focuses on rats, what are the potential implications of these findings for human adolescents who consume alcohol and THC?

The study specifically investigated adolescent male rats, so the direct implications for adolescent humans require further research. However, the findings suggest that combining alcohol and THC can have significant and complex effects on appetite, weight, and potentially other cognitive functions in adolescents. These findings underscore the importance of understanding the potential risks associated with co-use during this critical developmental period. Future research should focus on understanding the specific mechanisms underlying these effects and determining whether similar effects are observed in human adolescents.

5

What exactly is Δ9-tetrahydrocannabinol (THC), and why was it specifically studied in this research?

Δ9-tetrahydrocannabinol, commonly known as THC, is the primary psychoactive compound found in cannabis. The study used THC to examine its effects, both alone and in combination with alcohol, on adolescent male rats. By isolating THC, the researchers could specifically assess its impact on ingestive behaviors and cognitive functions, providing insights into the potential consequences of marijuana use during adolescence. This targeted approach helps to differentiate the effects of THC from those of other compounds found in cannabis.

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