Early Cannabis Use Linked to Memory Slowdown in Teens
Marijuana use and memory deficits go hand in hand.
Posted May 1, 2026 | Reviewed by Ekua Hagan
A 2026 study of over 11,000 adolescents relied on self-report measures and toxicology reports to identify the cognitive effects of marijuana over time. These results shed new light on adolescent marijuana usage and how this affects the teenage brain.
Early marijuana use and intelligence
According to the results of this study, children between the ages of 9 and 12 who will eventually experiment with marijuana tend to score higher than their peers on several measures of behavior that contribute to intelligence . Those who try marijuana early in life tend to have faster and better short-term memory (like remembering a grocery list) and improved episodic memory. Episodic memory is the part of long-term memory that is tied to our emotions during personal experiences, such as remembering the thrill of riding a roller coaster for the first time.
Also common in those who will later become early users of marijuana is an increased rate of processing speed (how quickly or slowly we digest information), less impulsivity, improved language development, and a higher level of visuospatial skills, our ability to understand and mentally manipulate objects in space. (Think of your visuospatial skills as the ability to rearrange furniture in a room in your head.)
The relationship between early marijuana use and intelligence is fascinating and complex. Unfortunately for those who use marijuana in adolescence , these early intellectual advantages may be short-lived as a result of the marijuana use.
By the time these subjects reached their teenage years of 15 to 17 years of age, the intellectual growth in these arenas had plateaued, while their peers had continued to flourish.
Key cognitive skills decrease the most
Short-term memory, processing speed, and control of impulsive behaviors are all necessary not only for academic success, but also for everyday emotional regulation and decision-making . These skills rely heavily on the development of the prefrontal cortex and its rapid maturation during the adolescent years. The group that used marijuana showed significantly less improvement in these areas as they aged, even after controlling for alcohol , nicotine, and other substances in the sample population.
It’s the THC that gets you
This study also sought to examine the difference between the effects of THC and the effects of CBD , two different compounds in cannabis. The distinction, to put it simply, is that THC will make you high while CBD will not. In this study, some of the subjects tested positive for THC, while some tested positive for only CBD. Those who were exposed to THC showed slower improvement in episodic memory (long-term memory of their personal experiences) while those who were exposed only to CBD showed no difference from those who had not been exposed to THC.
This study relied on toxicology reports, not the honor system
In addition to the number of subjects and the length of time they were studied, this research is also notable for its use of hair toxicology to unearth the truth about participants' use of marijuana. Unsurprisingly, researchers learned that some of the teenagers were lying about their marijuana usage. The toxicology reports were also able to provide insight regarding the quantity of marijuana used, with some individuals falling into the category of moderate to heavy usage.
Delaying marijuana usage past age 16 may protect cognitive growth
If there is a takeaway message to come from the study, it is that experimenting with marijuana sooner is more detrimental for the developing brain. Sure, the severity of the effects of marijuana usage was related to the amount of marijuana consumed, but it was the early years of marijuana usage that caused the biggest negative effect on brain development.
Why is this important?
The small differences caused by early marijuana use are likely to result in slower gains in memory, processing speed, and/or impulse control that can add up to big differences over time that can influence academic performance and standardized testing, safe driving, and emotional regulation.
It is important for parents, clinicians, and teens to know that the issue of how marijuana affects the teenage brain isn’t necessarily a matter of abstinence but of timing. The adolescent brain is still under construction, and cannabis—especially THC—interferes with the brain's ability to create and hold onto important memories that form the foundation for future years.
Wade, N.E., Sullivan, R.M., Wallace, A.L. et al. Longitudinal neurocognitive trajectories in a large cohort of youth who use cannabis: combining self-report and toxicology. Neuropsychopharmacol. (2026). https://doi.org/10.1038/s41386-026-02395-1
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Lindsay Weisner, Psy.D., is a psychologist in private practice in Long Island, the author of Ten Steps To Finding Happy , and the host of the Neurotic Nourishment Podcast.
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This article is part of the Bringwise Psychology Journal — daily insights on human behavior, mental health, and personal growth.