What is "brain fog"?

                

"Brain fog" is not a medical diagnosis, but it is a term people often use to describe feeling mentally sluggish, distracted, forgetful, or unable to think clearly. Students experiencing brain fog may notice:

  • Difficulty concentrating in class
  • Trouble following instructions
  • Forgetting information learned recently
  • Slower thinking or problem-solving
  • Feeling mentally tired or "checked out"
  • Difficulty completing assignments or studying effectively

These are many of the same areas of thinking and memory that cannabis can affect.

How cannabis affects the brain

The active ingredient in cannabis that causes intoxication, tetrahydrocannabinol (THC), interacts with the brain's endocannabinoid system. This system helps regulate learning, memory, attention, mood, and decision-making. Because the brain continues developing until approximately age 25, young people may be especially vulnerable to the effects of cannabis.

Cannabis use can immediately affect:

  • Attention and concentration
  • Learning
  • Short-term memory
  • Processing speed
  • Decision-making

Cannabis may make it harder for students to move information from short-term memory into longer-term memory storage. This means a student may go to class and feel present, but later struggle to remember key concepts or details that were taught.

What does recent research show?

One study that followed more than 11,000 young people found that adolescents who began using cannabis showed slower growth in memory, attention, language, and processing speed compared with their peers who did not use cannabis.

Impact on school success

The effects of reduced focus, memory difficulties, and slower cognitive processing can extend beyond the classroom.
Research that included 63 studies and more than 438,000 participants found that cannabis use during adolescence and young adulthood was related to lower grades and more school-related difficulties.

Can the effects improve?

Some cognitive effects may lessen when a person stops using cannabis, particularly after a long period of quitting. However, some impacts on memory, attention, and learning may last longer, especially among people who started using cannabis under age 25 or who used it frequently over time.

Sources

  • Centers for Disease Control and Prevention (CDC). Cannabis and Teens (2024). [cdc.gov]
  • Centers for Disease Control and Prevention (CDC). Cannabis and Brain Health (2024). [cdc.gov]
  • National Academies of Sciences, Engineering, and Medicine. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research (2017), Chapter 11: Psychosocial. [nationalacademies.org]
  • Chan O, et al. Cannabis Use During Adolescence and Young Adulthood and Academic Achievement: A Systematic Review and Meta-analysis. JAMA Pediatrics. 2024;178(12):1280-1289. [pubmed.ncbi.nlm.nih.gov]
  • Wade N, et al. Longitudinal neurocognitive trajectories in a large cohort of adolescents following cannabis use onset. Neuropsychopharmacology, 2026. Summary available through UC San Diego and the University of California. [today.ucsd.edu], [universityofcalifornia.edu]
  • Queiroz APS, et al. Cognitive Effects of Cannabis Use: A Comprehensive Review Across Domains. Neurology International. 2025. [pmc.ncbi.nlm.nih.gov]