According to American researchers cannabis slows brain development in teenagers

A large American study of more than 11,000 teenagers revealed that those who used cannabis showed less progress in memory, attention, and processing speed at a key stage of brain development.
Most teenagers gradually improve their cognitive abilities throughout adolescence. However, in young people who use cannabis, this progress appears to slow down and plateau earlier than in their peers, according to a new study.

This study, published in the journal Neuropsychopharmacology, revealed that middle and high school students who used cannabis showed 20 to 50 percent slower progress in memory, attention, processing speed, and other fundamental cognitive skills.

Rather than describing a sharp decline in abilities, the researchers refer to a "flattening" of the usual developmental curve: skills continue to improve, but at a slower pace.

“Adolescence is a crucial period for brain development, and we’re finding that teenagers who start using cannabis aren’t progressing at the same rate as their peers,” said Natasha Wade, assistant professor of psychiatry at the University of California, San Diego, and lead author of the study, in a statement.

“These differences may seem small at first glance, but they can add up and impact learning, memory, and everyday functioning.”

Consistent use among teenagers
These findings come as cannabis use remains common among American teenagers: about one in three high school seniors reports using it in the past year, often starting as early as age 16. Legalization has spread to many states, and cannabis products have become more potent, raising concerns about regular use during this sensitive period of brain development.

A Slowdown in Cognitive Development
Most adolescents generally experience consistent year-over-year improvement in cognitive measures. However, in those who use cannabis, this progression curve has flattened considerably.
Researchers used data from the ABCD (Adolescent Brain Cognitive Development) study, a large American cohort study that follows children from the age of 9 or 10 and observes their cognitive development over time. The analysis covered seven years of data collected between late 2016 and early 2024, including more than 2,200 participants who had used cannabis at least once and 9,600 who had not.
Each year, participants completed a series of cognitive tests. These included tasks such as memorizing and ordering images, quickly comparing visual patterns to determine if they matched, and recalling word lists after short or longer delays.

Across all 11,000 participants, cognitive abilities generally improved from late childhood through adolescence, reflecting the brain's rapid development. However, adolescents whose cannabis use was confirmed—through self-assessments and toxicological analyses of hair, urine, saliva, and breath—showed a different trajectory.

"Teens [participating in the study] will naturally progress and improve, both because they are older and because they have already taken the test before," Natasha Wade told The Epoch Times in an email. "But based on our data, we found that teens who use cannabis did not progress at the same rate as those who do not, and sometimes showed virtually no improvement." In some cases, before they began using cannabis, some teens scored slightly higher than their peers. However, as they grew older and began using cannabis, their progress leveled off, while those who did not use it continued to improve.

The most affected cognitive areas
The gap was most pronounced in working memory, with progress recorded representing about half of what would have been expected. Slower progress was also observed in attention, processing speed, and other fundamental skills.

The researchers observed:

Working memory: the ability to retain and briefly use information – 50% slower progress
Episodic memory: recalling events or experiences – approximately 30% slower improvement
Processing speed: the speed at which the brain processes information – approximately 25% slower growth
Attention and self-control: approximately 20% slower progress
Visual skills

According to American researchers cannabis slows brain development in teenagers

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