Decoding Cannabis: does cannabis cause cognitive decline? What a 44-year study found

Welcome back to Decoding Cannabis, where we take a recently published study, trial, review or research paper focusing on medical cannabis, and break it down into something more easily digestible. 

Let’s be blunt: for more than a century, the general consensus on the potential health implications of cannabis has been shaped more by misinformation and entrenched stigma than actual science. Prohibition, public messaging, and cultural narratives have reinforced the idea that long-term cannabis exposure may lead to lasting cognitive damage, particularly around memory and brain health.

But over the past few decades, as access to legal medical cannabis treatment has expanded, research has begun to catch up. In many cases, that evidence is beginning to challenge long-held assumptions about the relationship between cannabis and neurological functioning.

This study is a perfect example of that shift.

Study overview

 

Why is the link between cannabis use and cognitive decline still debated?

The debate can, in large part, be traced back to a combination of historical stigma, inconsistent research, and the way cannabis has been discussed in both public and scientific settings. Over time, this has led to a fragmented evidence base, where short-term effects, long-term outcomes, and individual differences are simply not understood or just grouped together, despite being very different questions.

Short-term effects tend to dominate the conversation, particularly around memory and attention. But those effects are often taken out of context, or treated as if they automatically translate into long-term decline.

They don’t.

When you zoom out and look at cognitive function over decades, the picture becomes far less clear. Research hasn’t pointed in a single direction, and that’s where much of the confusion comes from.

There’s also a tendency to collapse different ideas into one. Changes in focus, everyday memory, and long-term cognitive decline are often grouped together, even though they represent very different processes.

That mix of short-term findings, long-term uncertainty, and blurred definitions around the causes of a decline in cognition is why the debate hasn’t settled. As a result, conversations around brain health often cross over with broader areas such as mental health conditions and sleep disorders, both of which can play a significant role in cognitive function over time.

What was the scope of this 44-year study?

Rather than looking at short-term effects, this study focused on long-term cognitive change across adulthood.

Titled “Cannabis Use and Age‐Related Changes in Cognitive Function From Early Adulthood to Late Midlife in 5162 Danish Men”, it compared cognitive performance across a cohort of men between early adulthood and late midlife. The same intelligence test was used for both assessments, allowing researchers to track change over time rather than relying on different methods or assumptions.

Alongside cognitive data, the study also accounted for a wide range of factors, including education, lifestyle, health, and substance exposure. This makes it less about isolated cannabis usage, and more about how cognitive decline plays out in the context of real life.

What did this study uncover about cannabis and cognitive decline?

Across the full sample, participants showed an average decline of around 6.2 IQ points over the 44-year period. This is very much in line with what we’d expect from long-term studies of cognitive ageing, rather than anything unusual or accelerated.

What did come as somewhat of a surprise to many was that, for the cohort who did report long-term cannabis usage, the cognitive drop-off was actually slightly lower than in non-users. The difference was small (1.3 IQ points), but consistent even when variables such as education, alcohol use, smoking, and broader health factors were considered.

Is a 1-point IQ difference actually meaningful?

No, a difference of around 1 IQ point isn’t overly significant. It doesn’t change how someone thinks, works, or functions. But it does show that, among long-term cannabis users, there was no evidence to support historical claims that it leads to a heavier than normal decline in mental performance.

Did early or frequent cannabis use make things worse?

The study didn’t find any clear link between starting earlier and worse long-term outcomes. The same goes for frequency - even for the men who used cannabis more regularly, there was no evidence of faster mental decline whatsoever. 

Does cannabis cause dementia?

This study did not look at dementia diagnoses directly. It focused on long-term changes in thinking ability over time, not whether participants went on to develop conditions like Alzheimer’s or other forms of dementia.

Based on this study, there is no clear evidence to suggest that cannabis causes dementia, or accelerates dementia onset.

At the same time, it’s important not to overstate the findings. 

This study doesn’t show that cannabis reduces dementia risk either. It simply suggests that the relationship between cannabis exposure and long-term brain health is not as clear-cut as often assumed.

But it’s also not that simple. This research looked at long-term changes in thinking ability, not clinical diagnoses. So while it challenges the idea that cannabis leads to accelerated decline, it doesn’t directly answer whether it influences dementia risk.

Looking more broadly, the evidence remains mixed. Some studies raise valid questions, while others highlight how cannabis may help manage the secondary symptoms of dementia for some patients. 

Is cognitive decline the same as dementia?

No.

A gradual decline in thinking ability is a normal part of ageing. Dementia, on the other hand, is a clinical condition. It involves more significant and progressive changes, often linked to underlying diseases such as Alzheimer’s.

What are the main limitations of this study?

As with any long-term study, there are a few important limitations to keep in mind.

• The sample only included men, which means the findings may not apply in the same way to women or more diverse populations.

• The study also relied on self-reported cannabis use, collected later in life. While common in this type of research, it does introduce some uncertainty, particularly when recalling patterns from decades earlier.

• There are also gaps in the detail. The study does not account for modern cannabis products, differences in potency, or how patterns of use may have changed over time.

• While the researchers adjusted for a range of lifestyle and health factors, it is not possible to completely isolate cannabis from everything else that influences long-term brain health.

What does this mean if you are considering medical cannabis treatment?

It’s important to separate what this study looked at from how medical cannabis is actually prescribed and used today.

This research focused on general population cannabis exposure, most of which would be considered nonmedical. Prescribed treatment is different. It’s structured, clinically guided, and built around the individual, with dosing, response, and outcomes monitored over time.

If you are considering this route, where you access treatment matters. Releaf is widely recognised as the most trusted medical cannabis clinic in the UK, supported by thousands of verified Trustpilot reviews and the fastest growing patient base in the UK.

How Releaf supports our patients

Patients are guided by a world-class clinical team of 50+ specialists, doctors, and nurses, alongside a fully UK-based Patient Support Team that is always on hand. Appointments are flexible and available seven days a week, making it easier to access consistent, ongoing care.

You’ll also receive a UK medical cannabis card, which provides a simple way to verify your prescription when needed. On top of this, all Releaf patient have access to free medical cannabis travel certificates, helping you navigate situations where proof of prescription may be required.

Ultimately, the focus of Releaf medical cannabis treatment is on targeted symptom management, supported by regular follow-ups to ensure your treatment remains appropriate and effective.

FAQs - Medical cannabis, brain health, dementia, and cognitive decline

Does cannabis affect memory long term?

Some studies suggest there may be changes over time, while others find little to no lasting impact once lifestyle and health factors are considered. In this study, those who had used cannabis showed slightly less decline in thinking ability than non-users, although the difference was small and not likely to be meaningful in everyday life.

Can cannabis increase dementia risk?

No, while concerns about a link have often been reinforced by misinformation and stigma, this study does not provide evidence that cannabis increases dementia risk. If anything, it strongly suggests that the participants who did use cannabis long-term had a slight positive edge over the non-users.

Is occasional cannabis use harmful to the brain?

For most people, occasional cannabis use is unlikely to have a lasting impact on brain function. Effects can vary depending on factors like age, overall health, and the type of product prescribed. Releaf’s world class clinical team is highly trained and has experience treating a wide range of conditions, using a personalised approach to ensure treatment remains appropriate and closely monitored over time.

Cannabis and long-term brain health: what this study really shows

This study doesn’t rewrite everything we thought we knew about cannabis and the brain, but it does shift the conversation, hopefully down a more positive and informed path. The biggest takeaway is this.

Long-term brain health is shaped by a wide range of factors. Education, lifestyle, overall health, and underlying conditions all play a role. Cannabis is just one piece of a much larger picture.

And like much of the research in this space, the story is still evolving. More data is needed, particularly across more diverse populations and modern patterns of use.

If you are considering treatment, you can check your eligibility today with Releaf’s medical cannabis eligibility checker. It’s free, takes less than 20 seconds, and gives you a clearer idea of your potential eligibility.

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