March 8, 2023 – With this introduction, I want to turn attention to Madeline Meier’s important new article, “Long-term Cannabis Users Show Lower Cognitive Reserves and Smaller Hippocampal Volume in Midlife.”[4] Meier’s article offers a critical sequel to previous descriptions of the Dunedin, NZ, cohort of over a thousand people born in 1972-1973 who have now been studied into their fifth decade. After measuring baseline cognitive abilities at age 13 (before any drug use), each was interviewed about their substance use at 18, 21, 26, 32, 38, and now 45. Thorough neurocognitive testing at 38 revealed that individuals who started cannabis use during adolescence and persisted through adulthood experienced an average eight-point IQ decline since age 13. 

Meier now reports the results of interviews and neurocognitive testing at age 45. Control groups include people who have never used cannabis, those with long-term tobacco use, those with long-term alcohol use, those who use cannabis recreationally (less than weekly), and those who have quit cannabis.


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