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Cannabis Use and IQ Decline

Research has shown a relation between cannabis use and IQ decline. The National Institute on Drug Abuse has done a 25 year cannabis and IQ decline research study on 1,000 individuals based in New Zealand. Their findings have shown that frequent cannabis use before the age of 18 had lower IQ points in proportion to how often they used the drug. The cannabis users cognitive decline was noticeable to family and friends, and also could be measured on psychological tests. Studies have also shown that cutting back or quitting among youth cannabis users did not fully improve their IQ loss.


  • Cannabis use can lead to cognitive decline, memory loss and decline in IQ
  • IQ loss was not fully improved during the study by NIDA
  • Cannabis use can lead to addiction

Cannabis Harms Young Brains

Studies done by Dr. Meier, and findings by colleagues have shown that the IQ is quite vulnerable to exposure of cannabis in adolescence. There was evidence of significant decline in IQ that only affected adolescent cannabis users. There was little difference in IQ loss in those who used cannabis weekly before age 18 and stopped or reduced for a year or more by age 38, versus those who used cannabis more frequently. Currently more research needs to be conducted to see if cannabis related IQ loss is reversible.



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