Home > the mind, work > marijuana’s effect on the brain – notes

marijuana’s effect on the brain – notes

Neurological effects

Experiments on animal and human tissue have demonstrated disruption of short-term memory,[10] which is consistent with the abundance of CB1 receptors on the hippocampus, the region of the brain most closely associated with memory. Cannabinoids inhibit the release of several neurotransmitters in the hippocampus, like acetylcholine, norepinephrine, and glutamate, resulting in a major decrease in neuronal activity in that region. This decrease in activity resembles a “temporary hippocampal lesion.”[10] In the end, this process could lead to the blocking of cellular processes that are associated with memory formation.

Cannabis consumption affects motor skills, reflexes, and attention, which is important when considering its effects on driving; however, this does not necessarily reflect impairment in terms of performance effectiveness, since few studies report increased accident risk.


The fungi Aspergillus flavus,[28] Aspergillus fumigatus,[28] Aspergillus niger,[28] Aspergillus parasiticus, Aspergillus tamarii, Aspergillus sulphureus, Aspergillus repens, Mucor hiemalis (not a human pathogen), Penicillin chrysogenum, Penicillin italicum and Rhizopus nigrans have been found in moldy cannabis.[27] Aspergillus mold species can infect the lungs via smoking or handling of infected cannabis and cause opportunistic and sometimes deadly Aspergillosis.[citation needed] Some of the microorganisms found create aflatoxins, which are toxic and carcinogenic. Researchers suggest that mouldy cannabis thus be discarded.

Mould is also found in smoke from mould infected cannabis,[27][28] and the lungs and nasal passages are a major means of contracting fungal infections. “Levitz and Diamond (1991) suggested baking marijuana in home ovens at 150 °C [302 °F], for five minutes before smoking. Oven treatment killed conidia of A. fumigatus, A. flavus and A. niger, and did not degrade the active component of marijuana, tetrahydrocannabinol (THC).”[27]


Cannabis contaminated with Salmonella muenchen was positively correlated with dozens of cases of salmonellosis in 1981.[29] “Thermophilic actinomycetes” were also found in cannabis.[28]Research shows that although marijuana is in many ways detrimental to a person’s health, it is not so much on the physical side, but more psychological that is apparent. You can get in the habit of using it to fall asleep and get the mind to stop racing or review the thoughts about the day, a person in your past or job and financial anxiety. The body’s cerebellum and serotonin then gets used to this being a way to tune things out rather than developing a way to process emotions and stay calm in the midst of negative feelings. Over long term marijuana use (over five years, per adum), there have been numerous harmful effects of marijuana to the body’s ability to create natural and necessary “feel good” chemicals. In a recent study conducted by Imperial College London, subjects who had smoked cannabis during a five trial, presented with 68% less serotonin than subjects who were unexposed to cannabis.

Marijuana’s Effects Linger in the Brain

Blood Flow to Brain Altered Weeks After Smoking Pot
By Jennifer Warner
WebMD Health News

Feb. 7, 2005 – The effects of marijuana in the brain may linger long after the last joint goes out.

A new study shows that blood flow to the brain in people who smoked marijuana remained altered up to a month after they last smoked pot.

Researchers say the findings may help explain the problems with memory and thinking found in previous studies of chronic marijuana users.

Marijuana’s Effects on the Brain

In the study, which appears in the Feb. 8 issue of Neurology, researchers studied the blood flow in brain arteries of 54 marijuana users and 18 nonusers.

The marijuana users volunteered to participate in an inpatient program and abstained from marijuana use for a month.

Blood flow in the brain was analyzed at the beginning of the study and at the end of the month for the marijuana users.

Researchers found blood flow was significantly higher in marijuana users than in nonusers, both at the beginning and at the end of the study.

However, the marijuana users also had higher scores on the pulsatility index (PI), which is a measure of resistance to blood flow.

Researchers say the level of resistance to blood flow among light and moderate marijuana users improved over the course of the abstinence month. But there was no improvement among heavy marijuana users.

This resistance is thought to be caused by the narrowing of blood vessels that happens when the body’s own ability to regulate the circulatory system becomes impaired.

“The marijuana users had PI values that were somewhat higher than those of people with chronic high blood pressure and diabetes,” says researcher Ronald Herning, PhD, of the National Institute on Drug Abuse in Baltimore, Md., in a news release. “However, their values were lower than those of people with dementia. This suggests that marijuana use leads to abnormalities in the small blood vessels in the brain, because similar PI values have been seen in other diseases that affect the small blood vessels.”

Light marijuana users smoked two to 15 joints per week, moderate users smoked 17 to 70 joints per week, and heavy users smoked 78 to 350 joints per week.

ScienceDaily (Oct. 15, 2008) — Brain imaging shows that the brains of teens that use marijuana are working harder than the brains of their peers who abstain from the drug.

At the 2008 annual meeting of the American Academy of Pediatrics in Boston, Mass., Krista Lisdahl Medina, a University of Cincinnati assistant professor of psychology, presented collaborative research with Susan Tapert, associate professor of psychiatry at the University of California, San Diego.

Medina’s Oct. 12 presentation, titled, “Neuroimaging Marijuana Use and its Effects on Cognitive Function,” suggests that chronic, heavy marijuana use during adolescence – a critical period of ongoing brain development – is associated with poorer performance on thinking tasks, including slower psychomotor speed and poorer complex attention, verbal memory and planning ability. Medina says that’s evident even after a month of stopping marijuana use. She says that while recent findings suggest partial recovery of verbal memory functioning within the first three weeks of adolescent abstinence from marijuana, complex attention skills continue to be affected.

“Not only are their thinking abilities worse, their brain activation to cognitive tasks is abnormal. The tasks are fairly easy, such as remembering the location of objects, and they may be able to complete the tasks, but what we see is that adolescent marijuana users are using more of their parietal and frontal cortices to complete the tasks. Their brain is working harder than it should,” Medina says.

She adds that recent findings suggest females may be at increased risk for the neurocognitive consequences of marijuana use during adolescence, as studies found that teenage girls had marginally larger prefrontal cortex (PFC) volumes compared to girls who did not smoke marijuana. The larger PFC volumes were associated with poorer executive functions of the brain in these teens, such as planning, decision-making or staying focused on a task.

Medina says adolescence is a critical time of brain development and that the findings are yet another warning for adolescents who experiment with drug use. She says more study is needed to see if the thinking abilities of adolescent marijuana users improve following longer periods of abstinence from the drug. “Longitudinal studies following youth over time are needed to rule out the influence of pre-existing differences before teens begin using marijuana, and to examine whether abstinence from marijuana results in recovery of cognitive and brain functioning,” says Medina.

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