Most teenagers become cognitively sharper through adolescence.
However, in teens who use cannabis, cognitive growth appears to slow—leveling off earlier than in their peers—according to a new study.
The study, published in Neuropsychopharmacology, found that middle and high school-age teens who used cannabis showed 20 percent to 50 percent slower gains across memory, attention, processing speed, and other core cognitive abilities.
Rather than sharp drops in ability, researchers describe a “flattening” of the typical developmental curve—skills continue to improve, but less steeply.
“Adolescence is a critical time for brain development, and what we’re seeing is that teens who start using cannabis aren’t improving at the same rate as their peers,” Natasha Wade, an assistant professor of psychiatry at the University of California–San Diego, and the study’s lead author, said in a statement.
“These differences may seem small at first, but they can add up in ways that affect learning, memory, and everyday functioning.”
The findings come as cannabis use remains common among U.S. teenagers, with about one in three high school seniors reporting use in the past year, often beginning at about age 16. Legalization has expanded across many states, and cannabis products have become more potent, raising concerns about regular use during this sensitive period of brain development.
A Plateau of Cognitive Growth
The natural trajectory for most teens is steady year-over-year improvement across cognitive measures. Among those using cannabis, that growth curve flattened significantly.
The researchers used data from the Adolescent Brain Cognitive Development, or ABCD Study, a large U.S. cohort that follows children starting at ages 9 and 10 and tracks their cognitive development over time. The analysis covered seven years of data collected from late 2016 through early 2024, including more than 2,200 participants who used cannabis at least once and 9,600 who did not.
Participants completed a range of cognitive tests every year. These included tasks such as remembering and sequencing images, quickly comparing visual patterns to determine whether they match, and recalling lists of words after short and longer delays.
Across all 11,000 participants, cognitive skills generally improved from late childhood into adolescence, reflecting the brain’s rapid development. However, teens verified as cannabis users—through self-reports and toxicology testing of hair, urine, oral fluid, and breath—showed a different pattern.
“Teenagers [in the study] are naturally going to develop and improve, both because they are older and because they’ve done the test before,” Wade told The Epoch Times in an email. “But in our data, we saw that teens who use cannabis didn’t improve at the same rate as those who did not use cannabis, and sometimes they didn’t show much growth at all.”
In some cases, before cannabis use began, certain teens performed slightly better than their peers. However, as they got older and began using cannabis, their progress flattened, while nonusers continued to improve.
The clearest gap appeared in working memory, where gains were about half what would be expected. Slower improvement was also seen in attention, processing speed, and other core skills.
Across key domains, researchers observed:
- Working Memory: holding and using information briefly—50 percent slower improvement
- Episodic Memory: recalling events or experiences—about 30 percent slower improvement
- Processing Speed: how quickly the brain handles information—about 25 percent slower growth
- Attention and Self-Control: about 20 percent slower improvement
- Visual and Spatial Skills: about 15 percent to 20 percent slower improvement
- Reading and Language Skills: about 10 percent to 15 percent slower improvement
THC May Be Stalling Growth
Researchers focused on tetrahydrocannabinol (THC), the main psychoactive compound in cannabis, and cannabidiol (CBD), which does not produce a high.
Among a hair-testing subgroup of 645 youths aged 12 to 16, THC exposure in hair was linked with weaker gains in episodic memory—recalling specific events or experiences. CBD exposure did not show the same pattern, although the authors cautioned that the sample size was too small for firm conclusions and that CBD products may still contain THC because of contamination or mislabeling.
The biological testing—which caught about one-third of cannabis users whom self-reporting alone would have missed—strengthened confidence in identifying cannabis exposure in the study.
“Using a lot of cannabis during this time may delay or interrupt that healthy development, reducing the gains in cognition we would expect during the teenage years,” Krista Lisdahl, a clinical neuropsychologist at the University of Wisconsin and co-author of the study, told The Epoch Times in an email.
The likely mechanism involves the endocannabinoid system, a network of chemical signals that helps guide the development of neural connections during adolescence. THC closely resembles the brain’s own signaling molecules and binds to receptors involved in learning and cognition during this critical period of brain maturation.
Heavy THC exposure may also reduce the system’s natural signaling over time, making it less effective.
“If you use too much THC, the endocannabinoid system can downregulate—meaning the natural signal is reduced, and it cannot perform its job as effectively,” Lisdahl said. “This can disrupt healthy neurodevelopment and potentially reduce learning.”
The study did not directly test this mechanism. However, the researchers said it offers a plausible explanation for why teens who used cannabis appeared to follow a different developmental path—one in which cognitive gains unfolded more slowly.
Large Stakes During Development
The study does not establish cause and effect. Researchers adjusted for a range of potential confounding factors—including prenatal substance exposure, demographic variables, and childhood mental health—and the association held. However, Wade was careful to note the limits of what the data can show.
Across analyses, the group differences were modest. However, adolescence is a period of rapid cognitive development, and the brain continues developing into the mid-20s, making adolescence a particularly sensitive window for exposures that may influence how these skills unfold. Even small shifts in memory, attention, and processing speed can shape how teenagers learn and function day to day.
“Even modest shifts can be meaningful at a population level if they affect many individuals or involve cognitive domains,” Susan F. Tapert, a distinguished professor of psychiatry at the University of California–San Diego and a co-author of the study, told The Epoch Times in an email. “But they should still be interpreted cautiously and not as deterministic for any individual.”
Over time, those gaps may widen, shaping academic progress and everyday decisions—from focusing in class to reacting quickly while driving, where teens already face higher risks.
It is unclear whether those differences can reverse if teens stop using cannabis.
“Some studies suggest certain thinking abilities may recover while others may not,” Wade said. “Future work with this cohort will help clarify whether the effects are long-lasting.”
The researchers agree that the takeaway is clear: Avoiding cannabis use—especially products containing THC—during adolescence supports healthier brain development.