Study shows frequent marijuana use may impair key memory skills, affect job performance
Cannabis remains one of the most commonly used illicit substances worldwide, with approximately 147 million people — about 2.5 per cent of the global population — consuming it annually.
A recent study published in JAMA Network Open suggests that frequent use of marijuana, also known as cannabis, can impair working memory, potentially affecting safety, communication, and job performance.
Cannabis remains one of the most commonly used illicit substances worldwide, with approximately 147 million people — about 2.5 per cent of the global population — consuming it annually.
More To Read
The research analysed data from over 1,000 past or current cannabis users, collected as part of the Human Connectome Project between 2012 and 2015.
Participants, aged 22 to 36, underwent brain scans while completing cognitive tests measuring memory, decision-making, emotional processing, and social interactions.
Urine samples helped classify them into three groups: heavy users (over 1,000 lifetime uses), moderate users (10-999 uses) and non-users (fewer than 10 uses)
Results showed that heavy cannabis users had reduced brain activity in regions responsible for memory, decision-making, and focus.
Lead author Joshua Gowin, an assistant professor of radiology at the University of Colorado’s Anschutz School of Medicine said working memory enables individuals to briefly retain and utilise information.
"For instance, when driving, you check your blind spot before merging. Your brain must hold that information momentarily to make a safe decision," Gowin said.
"Similarly, in a conversation with your boss, you need to remember what was just said to respond appropriately. If working memory is impaired, processing information becomes more difficult."
Cause-and-effect relationship
While the study highlights a connection between cannabis use and reduced working memory, it does not establish a direct cause-and-effect relationship, said Carol Boyd, a professor emerita at the University of Michigan’s Centre for the Study of Drugs, Alcohol, Smoking, and Health.
“For years, people have observed that heavy cannabis users struggle with memory — hence the stereotype of a ‘stoner’ who forgets grocery lists or can’t follow instructions,” Boyd noted.
However, one key question remains unanswered: Can working memory recover after quitting marijuana?
"If a teenager used cannabis over 1,000 times between ages 15 and 20 but quit at 20, would their memory improve a decade later?" Boyd asked. "That’s what we still need to understand."
Among heavy lifetime cannabis users, 63 per cent showed reduced brain activity during memory tasks. Similarly, 68 per cent of those who had used cannabis recently exhibited the same effect.
Long-term use
"When comparing recent versus chronic users, we found that long-term use had a greater impact on working memory than recent use," Gowin explained. "Heavy users had about 14 per cent less brain activation than non-users."
However, the study could not determine whether the impairment persisted after long-term abstinence.
The study noted that heavy cannabis users were more likely to be male, have lower educational and socioeconomic status, and consume alcohol or tobacco. However, alcohol use did not explain the memory deficits observed, researchers found.
Boyd pointed out that other factors, such as ADHD (attention deficit hyperactivity disorder)— also linked to memory problems — might have influenced the results. Additionally, the study could not measure tetrahydrocannabinol (THC) levels or differentiate between methods of consumption, such as smoking versus edibles.
The long-term effects of cannabis on memory remain uncertain.
Some studies suggest that abstaining from cannabis for a month can lead to partial memory recovery, but more research is needed.
“There is evidence that quitting alcohol can allow the brain to recover," Gowin said. "But with chronic cannabis use, we still don’t have definitive answers."
NACADA report
A report on drug and substance use in Kenya by the National Authority for the Campaign Against Alcohol and Drug Abuse (NACADA) reveals that nearly one million people consume cannabis, with 475,770 being male and 43,037 females. Among them, 193,430 youth aged 15-24 years — equivalent to one in every 37 — are using cannabis, reflecting a 2.7 per cent prevalence rate.
For individuals aged 25-35, the number stands at 174,142, or one in every 48, with a prevalence rate of 2.1 per cent.
The report highlights a staggering 90 per cent increase in cannabis consumption over the past five years, raising serious public health concerns.
The data also shows that 234,855 Kenyans aged 15-65 years — one in every 111 — are addicted to cannabis and suffer from severe substance use disorders. Among them, 90,531 individuals aged 15-24 (one in every 77) and 100,468 aged 25-35 (one in every 83) are classified as addicts, resulting in an overall addiction rate of 47.4 per cent.
The World Health Organisation (WHO) warns that cannabis use can have several negative effects on health. It impairs memory and learning, especially when used during the process of learning or recalling information.
Cannabis also affects motor skills, such as coordination and attention, and even small amounts can impair performance for up to 24 hours, increasing the likelihood of accidents.
Over time, chronic cannabis use can cause lasting damage to cognitive functions, such as memory and attention, and these effects may not go away even after quitting. Regular users are also at risk of developing dependence and losing control over their cannabis use. For people with mental health conditions like schizophrenia, cannabis use can make symptoms worse.
Smoking cannabis over a long period can harm the lungs, leading to airway damage, inflammation, and reduced ability to fight infections.
Heavy cannabis use is also linked to a higher risk of both chronic and acute bronchitis.
Additionally, using cannabis during pregnancy can harm foetal development, leading to lower birth weights and, although more research is needed, may also increase the risk of certain cancers in babies.
Top Stories Today
