Long term effects of cannabis use
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Long-Term Effects of Cannabis Use: Brain Structure and Function
Research shows that long-term, regular cannabis use is linked to changes in brain structure, particularly in areas rich in cannabinoid CB1 receptors. These include the medial temporal cortex, parahippocampal gyrus, insula, and orbitofrontal cortex, which are important for motivation, emotion, and affective processing. The degree of these changes is related to how often cannabis is used and the age at which use begins, with both heavy use and early onset increasing the risk of gray matter volume reduction. Some studies also report increased cerebellar volume, possibly due to developmental changes during adolescence 1310.
Cognitive Outcomes and Neurocognitive Deficits
Long-term cannabis use is associated with small to moderate deficits in cognitive domains such as executive function, learning, memory, and global cognition. Decision-making abilities may be moderately affected, while attention, working memory, and information processing show smaller or nonsignificant differences compared to non-users. These cognitive deficits persist even after periods of abstinence, though some functions, like executive function, may recover with prolonged abstinence. The duration of use and age of onset are important, with heavier and earlier use linked to greater deficits 356.
Functional and structural brain imaging studies reveal altered activation patterns and reduced volumes in the hippocampus and orbitofrontal cortex among long-term users, supporting the observed cognitive impairments 1356. Notably, IQ decline from childhood to midlife and informant-reported memory and attention problems are more pronounced in long-term cannabis users than in those who use tobacco or alcohol 68.
Mental Health and Psychiatric Risks
Long-term cannabis use is linked to an increased risk of mood disorders, exacerbation of psychotic disorders in vulnerable individuals, and the development of cannabis use disorder and withdrawal syndrome. People with pre-existing anxiety or mood disorders who use cannabis tend to experience higher symptom levels over time and less improvement from treatment. These negative outcomes are more likely with frequent and prolonged use 27910.
Physical Health and Ageing
Chronic cannabis use can contribute to cardiovascular and respiratory diseases. In midlife, long-term users show worse outcomes in biological ageing, health preparedness, financial preparedness, and social preparedness compared to non-users. However, many of these negative outcomes are also associated with polysubstance use (using multiple substances), making it difficult to attribute them solely to cannabis. Still, cannabis dependence itself is strongly linked to poorer social support and social preparedness in midlife 28.
Vulnerable Populations: Adolescents and Prenatal Exposure
Adolescents and individuals exposed to cannabis prenatally are particularly vulnerable to long-lasting effects. Early exposure is associated with greater risk for later mental health symptoms and cognitive deficits, especially in those with certain genetic backgrounds. Animal and human studies suggest that adolescent and prenatal cannabis exposure can have persistent effects on neural systems related to psychiatric and substance use disorders 110.
Conclusion
Long-term cannabis use is associated with structural brain changes, small to moderate cognitive deficits, increased risk of mental health problems, and challenges in healthy ageing and social support. The risks are higher with heavier use, early onset, and in vulnerable populations such as adolescents and those with pre-existing mental health conditions. While some negative outcomes are shared with other substance use, cannabis dependence itself remains a significant factor in cognitive and social challenges over time.
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