Marijuana’s main psychoactive chemical, THC, affects the brain by attaching to receptors in regions vital for memory formation, such as the hippocampus, amygdala, and cerebral cortex. The long-term use of marijuana, whether for medical or recreational purposes, can produce persistent cognitive impairments. Notably, cannabis plants with more than 0.3% THC by weight are classified as marijuana, while hemp contains 0.3% or less THC. Hemp products are thus less likely to cause an intoxicating effect. Marijuana is primarily cultivated for its flowers and is naturally high in THC, making it popular among recreational consumers.
Studies have shown that long-term cannabis users experienced an average IQ decline of 5.5 points from childhood, alongside deficits in learning and processing speed, when compared to non-users. The more frequently an individual used cannabis, the greater the cognitive impairment observed, suggesting a potential causative link. Additionally, early THC exposure can have long-term effects on how rewards are perceived in the brain, with the opioid system—responsible for promoting feelings of pleasure in response to rewards—being affected.
Despite the increasing legalization of marijuana for recreational and medical use, neuroscientists warn that cannabis may not be safe, especially for adolescents. THC binding to receptors in the brain hinders the formation of new connections, decreasing the number of synapse connections made, which impacts cognitive ability, learning, skill mastery, and concentration over time. Dr. Schuster’s research has shown that marijuana use in teens is associated with learning inefficiencies, with non-users performing better in several cognitive areas crucial for learning and academic achievement.
Furthermore, marijuana affects the brain in multiple ways. CB2 receptors, expressed in the midbrain’s ventral tegmental area on dopamine neurons, are believed to modulate the addictive properties of marijuana. Adolescents are particularly vulnerable to the long-term negative effects of THC on brain development. The use of marijuana before the brain is fully developed can result in changes to the brain, which is why consumption is restricted to individuals aged 21 or older. Higher levels of THC also increase the likelihood of negative reactions, such as panic, delusions, severe paranoia, and extreme confusion.
Harvard Health on Marijuana and Memory
Harvard Medical School on Cannabis and the Brain
Cognitive Effects of Long-term Cannabis Use in Midlife
Effects of Marijuana on the Developing Brain
Harvard Gazette on Cannabis Legalization and Safety
UCI Morning Sign Out on Marijuana and the Brain
Harvard Department of Psychiatry on Marijuana and the Teen Brain
Cobbers on the Brain: Understanding Marijuana and Your Brain
Marijuana’s Impact on Brain Immune Cells
Student Health and Counseling Services on Marijuana and Your Health