The findings give a clearer picture of how the drug could influence long-term health as users age.
While a 2024 study highlighted how smoking cannabis as a teenager can shape health several decades later, this research shifts the focus toward adults in mid-life.
It builds on earlier work but examines what happens when someone picks up the habit well past their teenage years.
This new research takes those concerns and asks a related question: does cannabis use affect cognitive abilities after the age of 40?
Previous long-term research suggested that regular users of the Class B drug had an average IQ drop of 1.3 points.
The difference was small enough that it did not change day-to-day life for most people, and those findings came from monitoring more than 5,000 men over a 44-year period.
A separate study from 2013 suggested that about 13.1 million people were dependent on it at the time.
With medical cannabis becoming more widely accepted for conditions such as chronic pain and nausea related to cancer treatment, researchers expect cannabis use to rise among older adults.
This shift makes understanding its long-term impact more important than ever.
The study method
Back in 2016, researchers launched a cohort study that followed 1,897 Australians who were between 40 and 46 years old when the project began.
Participants were studied again four years later, and then eight years after that, although only about 87 percent of the group took part in every round.
The team wanted to explore both within-person and between-person changes to see whether cannabis use had any connection to shifts in cognitive ability over time.
To do this, they used several cognitive tests, including the California Verbal Learning Test, which measures how well someone can recall lists of words across repeated trials.
Other assessments included the Symbol Digit Modality Test, which requires pairing symbols with numbers using a reference key, along with Digit Backwards tests and both simple and choice reaction time tasks.
Together, these tests offered a broad look at memory and processing speed.
Participants self-reported their cannabis use from the previous year each time they were surveyed so the researchers could capture consistent patterns in use.
Conclusions
The study found that people who used cannabis tended to show weaker immediate recall and slightly poorer delayed recall than those who did not.
These results suggested some reduced performance in verbal memory tasks among users.
Participants who did not use cannabis showed stronger results once researchers accounted for premorbid verbal ability and other factors linked to cannabis use.
There were no strong signs that cannabis users experienced faster cognitive decline as they aged.
In the end, aside from the lower verbal recall scores, the study found no solid evidence that cannabis caused accelerated cognitive decline in adulthood.
The poorer recall did not appear tied to a person’s current level of cannabis use, and overall, no clear pattern pointed to long-term cognitive damage among older users.
