A scientific look inside human brains at the long-term effects of marijuana (cannabis) use found some problematic evidence in areas of the brain associated with addiction. These studies report real, visible changes in the brain’s reward system related to the age of starting to use marijuana and/or the more it is used over time. These new findings reinforce earlier research showing harmful effects on teen’s cognition from use of cannabis. See Below for details.
Both recent human brain studies followed independent rat brain experiments indicating that marijuana affects the amygdala (controls emotional learning); and the nucleus accumbens (controls pleasure), areas in the brain associated with addiction. Previous studies have shown that other drugs known to be addictive – including cannabis-based chemicals – affect the brain’s reward centers (amygdala and nucleus accumbens) by creating changes in these addiction-related structures. But human studies are needed to make the leap from introducing cannabinoids in rat brains to knowing the effects of smoking pot on humans.
MRI brain scans of 40 young adult college students – 20 recreational marijuana users and 20 non-users, were studied. As reported in the Journal of Neuroscience, physical changes in volume, density and topography in both of the addiction associated amygdala and nucleus accumbens was seen in these human marijuana users, including in non-dependent, young adult users.
A second study of the effects of heavier pot use on the human brain is published in the Nature Neuropsychopharmacology. Again, MRI imaging compared heavy marijuana smokers to occasional smokers to see if overall brain changes are more extreme, the more you smoke. This study found reduced grey matter volume in nearly all brain regions that are rich in cannabis “receptors” including network structures that control motivation, emotion, and emotional learning.
The degree to which these brain areas changed was due to either heavy use or starting use during adolescence. Lighter users who started in their teens had the same grey matter volume reductions as long-term heavy users.
Regardless of one’s position on recreational marijuana use, these studies strongly suggest that cannabis use at any level is not free of possible addiction and that this drug can influence your behavioral/emotional health, especially for young persons.
EDITORS NOTE: This study reinforces a report posted on MemoryZine on June 3, 2011
( Early Teen Exposure to Cannabis May Damage Brain and Impair Short-term Memory) reprinted below for your convenience:
A unique study, published in the British Journal of Psychiatry reports convincing evidence that early use of cannabis can damage adolescent brain cells and impair mental capabilities, including short term memory performance.
Researchers found youths who were chronic cannabis smokers before their 15th birthday were at an elevated risk of neuropsychological problems compared to those who used the illicit drug at a later stage of life.
Experts generally agree that the most common illicit drug used by adolescents, cannabis, suppresses activities in the brain that control the level of consciousness.
In the study, early cannabis users performed poorly in tasks involving executive functioning, concentration and perseverance compared to the late users and controls. Researchers found that early-onset, but not late-onset, chronic cannabis users had deficits in their cognitive functioning, probably because the brains of youths younger than 15 are still developing. Until their brains mature, say after age 20, they appear to be particularly vulnerable to the neurotoxic effects of cannabis, leading to lower mental flexibility including poor memory performance.
The researchers carried out a study of 104 young chronic cannabis users to determine whether early exposure to cannabis use can cause damage to teen’s brain; 49 started using the drug prior to age 15 (early-onset users) while the rest began smoking pot after they reached 15 (late-onset users).
The early users had smoked cannabis for nearly 10.9 years; the late users had abused the drug for an average of 8.7 years. The study also recruited another 44 teens who didn’t use cannabis.
The subjects participated in a series of mental exercises designed to assess any neurological impact of early cannabis use. While researchers found no significant differences in IQ levels of the three groups, early cannabis users did poorly in tasks involving executive functioning, concentration and perseverance— making more mistakes and were less able to complete categories in the card-sorting test— compared with late users and controls. The score card of non-users and late starters of pot use was the same.
While it is still unclear whether moderate use of pot in adult life poses any long-term neurological harm, such as for legitimate medical purposes, the evidence against youthful cannabis use, especially before the age of 15, is mounting. Results of this study suggest that is advisable to protect one’s memory fitness by limiting moderate cannabis use by youths younger than 16.