Cannabis and Brain Aging: Can weed keep your brain young?

Can weed protect your brain as you get older? We unpack a study linking lifetime cannabis use to larger brain volumes and better cognitive test scores in older adults—and investigate how those findings became headlines urging readers to “pass the pot to grandma.” Along the way, we explore collapsing categorical variables, confounding, clinically versus statistically significant results, multiple testing, and how a press release subtly changed a story. We also meet permanently stoned mice, learn about Carl Sagan’s surprising connection to cannabis research, and discover how a single missing word can change the entire meaning of a study. Statistical topics Categorical variables Confounding Effect size False discovery rate Healthy volunteer bias Measurement error Multiple testing Observational studies Recoding variables Science communication Statistical vs practical significance Methodologic Morals “Always follow the chain from data to result to conclusions and pay attention to the words along the way.” “Huge samples can give tiny differences delusions of grandeur.” References Guha A, Fu Z, Calhoun V, Hutchison KE. Lifetime Cannabis Use Is Associated With Brain Volume and Cognitive Function in Middle-Aged and Older Adults. J Stud Alcohol Drugs. 2026;87(4):739-751. doi:10.15288/jsad.25-00346 Press Release: https://news.cuanschutz.edu/news-stories/study-finds-cannabis-usage-in-middle-aged-and-older-adults-associated-with-larger-brain-volume-better-cognitive-function Bilkei-Gorzo A, Albayram O, Draffehn A, et al. A chronic low dose of Δ9-tetrahydrocannabinol (THC) restores cognitive function in old mice. Nat Med. 2017;23(6):782-787. doi:10.1038/nm.4311 NY Post: https://nypost.com/2026/02/07/health/cannabis-may-benefit-aging-brains-study-finds/ David Grinspoon: https://www.nytimes.com/2020/07/02/science/lester-grinspoon-dead.html?unlocked_article_code=1.7lA.CyS1.neeqGGNgx8g1&smid=url-share Kristin and Regina’s online courses:  Demystifying Data: A Modern Approach to Statistical Understanding   Clinical Trials: Design, Strategy, and Analysis  Medical Statistics Certificate Program   Writing in the Sciences  Epidemiology and Clinical Research Graduate Certificate Program  Programs that we teach in: Epidemiology and Clinical Research Graduate Certificate Program  Find us on: Kristin -  LinkedIn & Twitter/X Regina - LinkedIn & ReginaNuzzo.com (00:00) - Opening: The Brain on Drugs (00:37) - The Cannabis Headline (03:38) - The Claim: Brain Benefits for Older Adults (06:53) - The Mouse Study: Pothead Mice vs. Control Mice (11:25) - From Mice to Humans: UK Biobank (15:01) - Measurement Problems and Category Collapse (21:39) - Results: Statistically Significant, Clinically Meaningless (27:13) - Individual Brain Regions and Cherry-Picking (32:32) - Cognitive Tests: What Actually Matters (40:09) - How It Gets Lost in Translation (45:32) - Rating the Claim