Long-Term Cannabis Use Linked to Low IQ

Source: Freepik

A study, spread over four decades, has found that long-term cannabis users have low IQ and significant cognitive decline.

Compared to alcohol and other recreational drugs, cannabis is often hailed as a relatively safer drug due to its less addictive nature. However, with the drug becoming legal in several countries, its use has dramatically increased in recent years. Although previous research has linked it to cognitive decline, none have followed patients from childhood to adulthood. Now, a study spread out over four decades has found a link between long-term cannabis use and low IQ in participants.

The Dunedin study began back in 1972 in Dunedin, New Zealand. Although originally designed to investigate child health and development, researchers soon expanded it to study the long-term effects of various factors. Recently, the team collected data on the lives of 1,000 individuals from birth to middle age. The researchers assessed the participants for cannabis use and dependence at the ages of 18, 21, 26, 32, 38, and 45. الكرابس They further assessed their IQ at ages 7, 9, 11 and 45. مراهنات سباق الخيل

Worse Than Alcohol or Tobacco

Results revealed that long-term cannabis use caused a decline in IQ from childhood to midline. These individuals also performed significantly worse on cognitive tests than people with no history of cannabis use. Furthermore, compared to long-term alcohol or tobaccos users, they showed more memory and attention problems, and poorer learning ability. According to the study authors, factors such as alcohol or tobacco use, family history of substance dependence, childhood socioeconomic status, or low childhood self-control can explain their findings.

Long-term cannabis users showed IQ decline from childhood to midlife (mean=−5. الربح الحقيقى من الانترنت 5 IQ points), poorer learning and processing speed relative to their childhood IQ, and informant-reported memory and attention problems.

study author

The researchers further conducted MRI scans of the cannabis users and non-users. Surprisingly, long-term cannabis use caused lower hippocampal volumes in individuals. The hippocampus is involved in learning and memory. A smaller hippocampal volume, coupled with cognitive issues, may also put these people at a higher risk of developing dementia.

In conclusion, cannabis might not be as safe as once assumed.


Meier, Madeline H., et al. “Long-Term Cannabis Use and Cognitive Reserves and Hippocampal Volume in Midlife.” American Journal of Psychiatry, 2022, doi:10.1176/appi.ajp.2021.21060664.


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