Cannabis is consistently reported to be the most consumed drug worldwide, yet it remains shrouded in stigma and misinformation. One persistent concern is the potential link between cannabis use and cognitive decline. However, while there is substantial evidence of potential short-term side effects of cannabis use on cognition and cognitive development – little research has assessed its association with age-related cognitive decline.
A recently published study in JAMA Psychiatry aimed to investigate how cannabis use affects age-related cognitive decline from early adulthood to late midlife. The researchers also investigated whether the age of initiation of cannabis use influenced the number of years of frequent use.
Data from the Danish Ageing and Cognition Cohort
Data was extracted from the Danish Ageing and Cognition cohort (DanACo), which tracked over 5,000 men for approximately 44 years, from early adulthood to late midlife. Researchers analysed the relationship between cannabis use (including age of initiation and frequency) and changes in cognitive function over time. Participants with an average age of 20.4 completed the conscription board intelligence test at baseline with an average retest interval of 44 years.
Follow-up studies compared baseline test scores with those from the follow-up examination and included a comprehensive questionnaire on lifestyle, health, and socioeconomic factors. Of the 5,340 men who participated in the follow-up studies, 5,162, for whom relevant data was available, were included in the current study.
Key Findings of the Study
Of the 5,162 eligible participants from the DanACo, 39.3% had used cannabis at least once. The majority of cannabis users (51.1%) initiated use before the age of 18, while 43.5% initiated use when aged 18-25 and 5.4% after the age of 25.
- Cannabis use and IQ at baseline: Cannabis users had a slightly higher IQ at conscription than non-users.
- Effects on cognitive decline: Cannabis users demonstrated less cognitive decline compared to non-users, with a mean difference of 1.5 IQ points in the unadjusted model and 1.3 IQ points in the adjusted model.
- Initiation of cannabis use and cognitive decline: The results showed no significant associations between the age of initiation of cannabis use and cognitive decline.
- Frequency of cannabis use and cognitive decline: Only a small proportion of cannabis users (10.1%) reported frequent cannabis use in their lifetime (using twice a week or more) and this was not associated with significant differences in cognitive decline.
The mean cognitive decline across the population of 5,162 Danish men was found to be 6.2 IQ points over an average of 44 years. Interestingly, cannabis users from this cohort exhibited less cognitive decline than non-users. However, this difference was modest and may not be clinically significant. Nonetheless, these findings provide interesting insights into the potential effects of cannabis on long-term cognition.
What This Means for Medical Cannabis Patients
Medical cannabis has been available in the UK since 2018 and an ever-growing population of patients are discovering its benefits. However, significant stigma remains around this class of medications, potentially due to the perceived negative cognitive effects of cannabis. This research offers an important insight into the relationship between cannabis use and long-term cognitive function.
However, further studies are required to better understand whether there truly are no adverse effects on cognitive decline or whether these effects are temporary and disappear over a prolonged period. While this study focused on middle-aged men, future research should explore the long-term effects of cannabis use in diverse populations, including women and older adults.
