Study Links Cannabis Use to Decreased Odds of Cognitive Decline

    Marijuana use is associated with lower odds of subjective cognitive decline (SCD), according to a new study, with people who consume cannabis for recreational or medical purposes reporting less confusion and memory loss compared to non-users.

    The study—which showed that recreational cannabis use is “significantly” linked to lower SCD—is especially notable given that past research has connected subjective decline to the development of dementia later in life.

    The results, published in the journal Current Alzheimer Research in February, indicate that THC’s impacts on cognitive function may be more complicated than popularly assumed.

    “Compared to non-users,” the authors wrote, “non-medical cannabis use was significantly associated with 96% decreased odds of SCD.”

    People who reported using marijuana for medical purposes, or for both medical and recreational purposes, also showed “decreased odds of SCD, although not significant,” the study found.

    To be sure, a number of earlier studies have indicated negative associations between heavy cannabis use and mental performance. The authors of the new study, out of SUNY Upstate Medical University in Syracuse, New York, pointed to past results linking long-term or frequent cannabis use to compromised verbal recall performance, worsened cognitive function and subjective memory complaints, for example.

    “However, the cognitive implications of cannabis are not only determined by the frequency of cannabis consumption,” they wrote, noting that other factors—including product formulation, method of administration and reason for use—may also “impact the cognitive effects associated with cannabis use.”

    “Our study addresses these knowledge gaps by comprehensively examining how reason, frequency, and method of cannabis use are associated with SCD among US middle-aged and older adults,” they wrote.

    Their survey asked respondents, “During the past 12 months, have you experienced confusion or memory loss that is happening more often or is getting worse?” They could respond yes, no, don’t know/not sure, or refuse the question.

    Results were analyzed across three cannabis variables: frequency of use over the past month, ranging from zero to 30 days; reason for cannabis use, which included non-user, medical, non-medical or both; and the method of cannabis consumption—non-user, smoke, eat, drink, vaporize, dab or other.

    The authors suggested several possible theories, including that people often use marijuana to cope with insomnia.

    “We found that non-medical cannabis use was significantly associated with reduced odds of SCD in comparison to non-users,” the study said, noting a number of possible explanations for the findings.

    To arrive at the findings, the researchers looked at health survey data from the 2021 Behavioral Risk Factor Surveillance System (BRFSS). The system’s cognitive decline module, they said, “was restricted to respondents aged 45 years and older in Washington DC and 14 US states (GA, HI, MS, OR, PA, TN, TX, WI, CO, MD, MI, OH, OK, and NY).”

    The total sample included 4,744 observations with valid SCD responses.

    The authors suggested several possible theories for why cannabis use could be tied to lower self-reported cognitive decline, including that people often use marijuana to cope with insomnia and other sleep issues—noting that a recent study found that “more frequent sleep disturbances were associated with higher dementia risk in a national US older adult sample.”

    “Several studies have found that cannabis use might enhance sleep quality, expedite sleep onset, and reduce sleep disturbances. Non-medical cannabis use could have contributed to the observed decrease in SCD due to its potential benefit on sleep quality,” the discussion section of the new paper said.

    The SUNY researchers also pointed out that “many people use cannabis to alleviate stress.”

    The SUNY researchers also pointed out that “many people use cannabis to alleviate stress,” noting that past studies have “shown that CBD could effectively reduce stress, and elevated stress levels could be associated with reduced cognitive function among older adults.”

    They also pointed to a 2017 mice study indicating that very low doses of THC could improve cognitive impairment among older females.

    Some of the results of the new study were mixed, however, including an association between the method of cannabis use and SCD. “In general,” the authors wrote, “SCD was more common among those who used cannabis through any method. Especially for cannabis smokers, there was a higher prevalence of SCD (11.2%) compared to no reported SCD (4.7%).”

    Some tests also showed a statistically significant association between cannabis use frequency and SCD. “The average days of cannabis consumption for those who had SCD (mean=8.68, SD=3.14) was significantly higher than the average days of cannabis use for those who did not have SCD (mean=5.44, SD=1.20),” the study found.

    Nevertheless, the authors wrote, “Although increased frequency and different methods of cannabis use showed positive associations with SCD, these relationships were not statistically significant.”

    Notably, the results also showed SCD was more common in people who reported using cannabis for medical, or both medical and non-medical, reasons, compared to those who used it only for non-medical reasons.

    The study was published in its “article in press” stage, meaning that while it has been accepted by the journal, copyedited and formatted, it may receive further proofreading changes or corrections by authors before it’s final.

    “Further research is needed to examine whether our observed associations may remain for more objective measures of cognitive impairment.”

    Among its limitations, authors noted, is the possible bias in responses by people in states where non-medical cannabis use remains illegal. “Given that the information on cannabis usage was self-reported,” it notes, “individuals in such states may be more likely to underreport or misreport their cannabis use.”

    The study also did not look at possible differences by geographic location, noting that some research has found cannabis-use increases over the past decade were more significant in states that legalized adult-use marijuana.

    “Finally, all questions in the BRFSS cognitive decline module are self-reported by the respondent, including the SCD variable,” the authors wrote. “Thus, further research is needed to examine whether our observed associations may remain for more objective measures of cognitive impairment.”

    The study is not a rejection of past findings that frequent or heavy cannabis use may carry cognitive risks, but instead an indication that more detailed study is needed.

    “Our findings underscore the importance of considering multiple factors, such as the reasons for cannabis use, when examining the relationship between between cannabis and SCD,” the authors concluded. “Further research is needed to explore the underlying mechanisms contributing to these associations.”


    A Fast-Growing Body of Research

    The study is among a growing body of research around marijuana as more jurisdictions move to end prohibition of the drug. An analysis late last year by the advocacy group NORML found that journals have published more than 32,000 scientific papers on marijuana over the past 10 years, including upwards of 4,000 in 2023 alone.

    A 2023 study examining marijuana’s neurocognitive effects found that “prescribed medical cannabis may have minimal acute impact on cognitive function among patients with chronic health conditions.”

    The authors of that study, published in the peer-reviewed journal CNS Drugs, wrote that they found “no evidence for impaired cognitive function when comparing baseline with post-treatment scores.”

    While the long-term effects of cannabis use are far from settled science, findings from a number of recent studies suggest some fears have been overblown.

    A report published in 2023 that drew on dispensary data, for instance, found that cancer patients reported being able to think more clearly when using medical marijuana. They also said it helped manage pain.

    “Clinical high-risk youth who continuously used cannabis had higher neurocognition and social functioning over time.”

    A separate study of teens and young adults at risk of developing psychotic disorders found that regular marijuana use over a two-year period did not trigger early onset of psychosis symptoms—contrary to the claims of prohibitionists who argue that cannabis causes mental illness. In fact, it was associated with modest improvements in cognitive functioning and reduced use of other medications.

    “[Clinical high-risk] youth who continuously used cannabis had higher neurocognition and social functioning over time, and decreased medication usage, relative to non-users,” the authors of that study wrote. “Surprisingly, clinical symptoms improved over time despite the medication decreases.”

    A separate study published by the American Medical Association (AMA) in January that looked at data from more than 63 million health insurance beneficiaries found that there’s “no statistically significant increase” in psychosis-related diagnoses in states that have legalized marijuana compared to those that continue to criminalize it.

    Results “did not support a causal relationship between marijuana use and IQ loss.”

    Studies from 2018, meanwhile, found that marijuana may actually increase working memory and that cannabis use doesn’t actually change the structure of the brain.

    And, contrary to then-President Trump’s claim that marijuana makes people “lose IQ points,” the National Institute of Drug Abuse (NIDA) said the results of two longitudinal studies “did not support a causal relationship between marijuana use and IQ loss.”

    Research has shown that people who use cannabis can see declines in verbal ability and general knowledge, but that “those who would use in the future already had lower scores on these measures than those who would not use in the future, and no predictable difference was found between twins when one used marijuana and one did not.”

    “This suggests that observed IQ declines, at least across adolescence, may be caused by shared familial factors (e.g., genetics, family environment), not by marijuana use itself,” NIDA concluded.



    Photograph by Elsa Olofsson via Flickr/Creative Commons 2.0

    This story was originally published by Marijuana Moment, which tracks the politics and policy of cannabis and drugs. Follow Marijuana Moment on Twitter and Facebook, and sign up for its newsletter.

    • Ben is a writer and editor covering cannabis since 2011, including as a senior news editor for Leafly. He is currently senior editor at Marijuana Moment. He lives in Seattle.

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