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Can Long-Term Cannabis Use in Dementia Worsen Cognitive Decline? 

Posted
Updated
ByMy Patient Advice
Author: Julia Sutton, MSc | Reviewed by: Dr. Clarissa Morton, PharmD

As medical cannabis becomes more widely discussed in the UK, many families wonder whether it might help or harm those living with dementia. According to recent evidence from NHS England, NICE, and Alzheimer’s Society UK, the impact depends largely on how cannabis is used, particularly the amount of THC and whether use is clinically supervised. 

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What The Research Says 

A 2025 study from the University of California found that low-frequency cannabis use (up to four times per month) in older adults, including those with mild cognitive impairment, did not worsen memory, executive function, or processing speed compared with non-users (PubMed Central, 2025). However, people with problematic or heavy cannabis use, often linked to cannabis use disorder, showed poorer memory and behavioural regulation. 

The long-running Dunedin Cohort Study (2024) reported that chronic, heavy THC exposure over many years was associated with IQ decline and smaller hippocampal volume, changes linked to long-term memory processing (PubMed, 2024). The findings suggest that risk lies not in occasional or medically guided use, but in frequent, high-THC exposure. 

A 2024 review published in Age and Ageing found no consistent evidence that properly supervised, low-dose medical cannabis accelerates neurodegeneration. Instead, high THC doses were more likely to cause temporary fatigue and inattention, effects that typically resolve with abstinence (Age and Ageing, 2024). 

NHS And NICE Guidance 

According to NHS England’s review of cannabis-based medicinal products, the main risks in older adults include sedation, confusion, and balance problems (NHS England, 2023). 

NICE guidance on dementia (NG97) advises against using cannabinoids to treat cognitive symptoms, while NICE guidance on cannabis-based medicinal products (NG144) highlights cognitive slowing and somnolence as common side effects of THC-dominant formulations (NICE, 2023). 

Alzheimer’s Society adds that heavy, long-term cannabis use may negatively affect memory and thinking, though evidence remains limited and further research is needed (Alzheimer’s Society UK, 2025). 

Clinical Bottom Line 

  • Light or medically supervised cannabis use does not appear to accelerate cognitive decline in dementia. 
  • Heavy, chronic THC exposure is linked with memory impairment and reduced cognitive control. 
  • CBD-dominant or balanced THC: CBD products show neutral or potentially calming effects, but evidence remains limited. 
  • Cannabis should only be considered under clinical supervision, with careful monitoring for confusion or balance problems. 

Educational Context: AlleviMed 

AlleviMed provides educational information about how medical cannabis eligibility is assessed within UK regulatory standards. The platform explains how licensed specialists evaluate conditions such as multiple sclerosis or chronic pain under current NHS and private frameworks. 

Takeaway 

Current research shows that occasional, clinically supervised cannabis use is unlikely to worsen cognitive decline in dementia, while heavy or unsupervised THC use may increase confusion and memory problems. Dementia care should continue to focus on evidence-based treatments and supportive care, with any interest in cannabinoid use discussed openly with a specialist. 

Julia Sutton, MSc
Author

Julia Sutton is a clinical psychologist with a Master’s in Clinical Psychology and experience providing psychological assessment and therapy to adolescents and adults. Skilled in CBT, client-centered therapy, and evidence-based interventions, she has worked with conditions including depression, anxiety, bipolar disorder, and conversion disorder. She also has experience in child psychology, conducting psycho-educational evaluations and developing tailored treatment plans to improve learning and well-being.

All qualifications and professional experience stated above are authentic and verified by our editorial team. However, pseudonym and image likeness are used to protect the author's privacy. 

Dr. Clarissa Morton, PharmD
Reviewer

Dr. Clarissa Morton is a licensed pharmacist with a Doctor of Pharmacy degree and experience across hospital, community, and industrial pharmacy. She has worked in emergency, outpatient, and inpatient pharmacy settings, providing patient counseling, dispensing medications, and ensuring regulatory compliance. Alongside her pharmacy expertise, she has worked as a Support Plan & Risk Assessment (SPRA) officer and in medical coding, applying knowledge of medical terminology, EMIS, and SystmOne software to deliver accurate, compliant healthcare documentation. Her skills span medication safety, regulatory standards, healthcare data management, and statistical reporting.

All qualifications and professional experience stated above are authentic and verified by our editorial team. However, pseudonym and image likeness are used to protect the reviewers's privacy. 

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