Does cannabis use affect cognitive decline?

A new study by Upstate Medical University researchers shows that recreational cannabis use may offer protection against cognitive decline.

The study, done by Master of Public Health (MPH) student Zhi Chen and Professor Roger Wong, Ph.D., MPH, MSW, analyzed a large data set from the CDC and found that compared to non-users, non-medical cannabis use, such as for recreational purposes, was significantly associated with 96 percent decreased odds of subjective cognitive decline (SCD). Medical and dual (medical and non-medical) use were also associated with decreased odds of SCD, although not significant. Cannabis consumption frequency and method were also not significantly associated with SCD.

SCD is an important outcome of interest as prior research shows individuals with SCD have a 2 times higher risk for dementia, which currently has no cure or definitive prevention approaches.

Wong said that previous studies have found negative associations between cannabis use and cognitive decline, so the results were surprising, though he is quick to point out the study had several limitations and that these results are just a snapshot of one year.

“The main takeaway is that cannabis might be protective for our cognition, but it is really crucial to have longitudinal studies because this is just a snapshot of 2021,” said Wong, assistant professor Department of Public Health & Preventive Medicine. “We do not know if non-medical cannabis leads to better cognition or the other way around if those with better cognition are more likely to use non-medical cannabis. We need longitudinal studies to see long term if non-medical cannabis use is protecting our cognition over time. That’s something we don’t know yet, but that research is hindered since cannabis remains illegal federally.”

Data for this study was obtained from 4,744 U.S. adults aged 45 and older in the 2021 Behavioral Risk Factor Surveillance System (BRFSS). SCD was a self-reported increase in confusion or memory loss in the past year. Odds of SCD by cannabis use reason, frequency, and method were examined after imputing missing data, applying sampling weights, and adjusting for sociodemographic, health, and substance use factors.

The study differs from previous research in that it focuses on middle-aged and older adults, and it uniquely considers the three facets of cannabis use: type of use (medical or non-medical), frequency of use, and mode of use (smoking, vaping, eating or dabbing).

“The reason I think this study is so great is we looked at all the different dimensions of cannabis use,” he said. “The fact that we included all three is a huge contribution to the research because I do not believe such a study has been done before.”

Wong said he was surprised that mode and frequency had no bearing on SCD since other studies involving younger participants found a negative connection between brain health and cannabis use, indicating perhaps that the age of the participants plays a role in the different results.

The study, which was published in Current Alzheimer Research was Chen’s final project in the Advanced Biostatistics course in the MPH program taught by Wong. 

“I applied the knowledge and analytical skills learned from the courses in the Public Health Methods concentration to this study,” Chen said. “Dr. Wong guided me through the process, from formulating a research question to preparing a full manuscript. I feel fortunate to have incredible professors in our program who train us to become well-rounded public health professionals with the skills for epidemiology and biostatistics work.”

The authors did note some limitations with the study, including the inability to consider state-by-state cannabis regulations; thus, potential selection bias could arise if the population of certain states is either over or underrepresented due to varying measures of cannabis use.

Strengths of the study include using a national data set, which increases the generalizability of the findings. Wong said the difference in protection between medical and non-medical use comes down to the compounds that make up cannabis. Medical-grade cannabis has higher concentrations of CBD whereas non-medical has higher concentrations of THC.

Non-medical users often use cannabis to improve sleep and reduce stress. Poor sleep and chronic stress increase the risk for dementia so the protection in SCD could come from better sleep and stress relief that cannabis provides. Medical cannabis is used primarily for pain relief.

“Based on our findings, we don’t see the CBD in medical cannabis being beneficial for cognitive health,” Wong said.

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