THC’s Impact on Brain Performance

While we are aware of the short-term physical effects from smoking or ingesting cannabis, scientists are learning weed can also have long-term impact on our brains. And exactly how THC effects can change the human brain most likely depends on the user’s age.

Cannabis activates the endocannabinoid system in the brain to produce its psychoactive effects. The endocannabinoid system plays an important role in brain development and regulating connections between neurons. Therefore, it makes sense that cannabis use can affect brain development in the adolescent brain.

This Is Your Brain on THC

When scientists looked at cognitive performance in adults who started using cannabis before the age of 17 and adults who started to use cannabis at age 17 or later, they found that early-onset users performed poorly on tasks that measured attention, impulse control, and planning, as well as had lower verbal IQ scores. These findings suggest that THC’s effects may be detrimental for the developing brain.

In addition to studies on young cannabis users, scientists used rodents to gain a better understanding of long-term THC effects on the brain and the mechanisms behind the effects. Researchers exposed adolescent rats to THC and found that THC-treated rats had significantly fewer cannabinoid receptors compared with animals that were untreated. THC treatment also altered the levels of other neurotransmitter receptors in the brain. Together, these changes led to an impairment of the endocannabinoid system, which persisted in the adult rat brain and caused cognitive deficits.

Adult Brains Can Benefit From THC

Cannabis use can clearly has a detrimental effect on the developing brain but what about the fully developed adult brain? In a recent study, researchers looked at the effects of prolonged exposure to a low dose of THC on young and old mice. Interestingly, they found that THC treatment restored learning and memory performance in old mice, and that these effects were long-lasting and persisted several weeks after treatment.

When the researchers looked at gene expression in the rats, they found that older rats treated with THC had an expression profile that closely resembled that of young mice, suggesting THC effects may increase the expression of anti-aging genes while decreasing the expression of genes that contribute to aging.

While these findings are compelling, it is important to remember that they do not give us a complete picture of cannabis and its long-term effects. There is still much that we do not know, so cannabis users of all ages should be cautious and aware of the potential effects of cannabis on their bodies.


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Rubino T et al. Adolescent exposure to THC in female rats disrupts developmental changes in the prefrontal cortex. Neurobiol Dis. 73: 60-69. 2015.
Bilkei-Gorzo A et al. A chronic low dose of delta-9-tetrahydrocannibinol (THC) restores cognitive function in old mice. Nat Med. 23(6): 782-787. 2017.