A study examining adults who smoke cannabis has shed light on whether the habit contributes to cognitive decline with age.
A newly published analysis explores the various ways cannabis use may influence individuals as they enter later adulthood. The findings offer a more defined understanding of how the drug could shape long-term health as users grow older. While a 2024 study highlighted the decades-long impact of smoking cannabis during the teenage years, this research shifts the lens toward adults in mid-life, building on earlier work by focusing on what happens when someone begins the habit well beyond adolescence.
Health experts have long cautioned that early cannabis use may disrupt brain development, with some comparing it to “growing your brain in a cannabis soup.” This new research raises a related question: does cannabis use impair cognitive performance after age 40? Previous long-term studies have suggested that regular users of the Class B drug experienced an average IQ decrease of 1.3 points — a small enough difference that it rarely affected daily functioning, based on data from more than 5,000 men tracked over 44 years.
Although many believe cannabis contributes to cognitive decline, a wide body of research has shown conflicting results.
According to reports from the United Nations Office on Drugs and Crime, roughly 178 million people worldwide use cannabis. A separate 2013 study estimated that around 13.1 million individuals were dependent on the drug at that time. As medical cannabis gains wider acceptance — particularly for chronic pain and nausea related to cancer treatment — experts expect usage to increase among older adults, making it even more critical to understand its long-term effects.
This research broke new ground by examining adults specifically. It follows earlier findings hinting at verbal learning difficulties among young adult cannabis users and investigates whether similar issues emerge later in life.
The study method
The project began in 2016, following 1,897 Australians who were between 40 and 46 years old at the start. Participants were reassessed four years later and again after eight years, though only around 87 percent completed every phase. The goal was to analyze both within-person and between-person changes to determine whether cannabis use corresponded with shifts in cognitive performance over time.
Researchers evaluated whether natural age-related cognitive changes differed between cannabis users and non-users. They applied multiple cognitive tests, including the California Verbal Learning Test (measuring how well individuals recall word lists across repeated trials), the Symbol Digit Modality Test (pairing numbers with symbols using a reference key), Digit Backwards tasks, and simple and choice reaction time assessments. Collectively, these offered insight into processing speed and memory.
To understand each participant’s verbal abilities before potential health-related changes, the team also administered a spot-the-word test during each study wave. Participants self-reported their cannabis use over the previous 12 months so researchers could track usage patterns consistently.
Study results showed that cannabis users typically displayed weaker immediate recall and slightly poorer delayed recall compared to non-users, indicating reduced performance in verbal memory tasks. Participants who did not use cannabis performed better once the researchers adjusted for premorbid verbal ability and other cannabis-related factors.
However, the team emphasized that these differences stemmed from comparisons between different individuals rather than declines within the same users over time. Crucially, there were no strong indications that cannabis users experienced faster cognitive decline with age. Aside from the reduced verbal recall scores, the research found no substantial evidence that cannabis accelerates cognitive decline in adulthood.
The weaker recall also did not appear linked to current levels of cannabis consumption, and overall, the results did not point to long-term cognitive harm among older users.
