Study finds long-term brain effect on Cannabis users

 But don't you want better oxygen delivery? Ask your competent? doctor to justify their stance on marijuana.

And this goes totally against what this aging research says:

chronic cannabis users have higher cerebral blood flow and extract more oxygen from brain blood flow than nonusers. August 2017

But this: 

Pot Smoking Baby Boomers Are On The Rise, Why Are Scientists So Happy For Them? Hint: Benefits For The Aging Brain

And this:

The Experiments Revealing How Marijuana Could Treat Dementia

And this;

Cannabis Use Linked to Lower Dementia Risk

The latest here:

Study finds long-term brain effect on Cannabis users

Prominence

Heavy lifetime cannabis use is associated with slightly lower brain activation during working memory tasks in young adults, with a Cohen effect size of -0.28. Recent cannabis use was also associated with lower performance and lower brain activation in working memory and motor tasks, although these associations did not remain significant after correcting for false discovery rate.

Context

• Cannabis use has increased globally, but its effects on brain function are not fully known, which highlights the need to better determine the results of recent and long-term brain activation from cannabis use.

• The legalization of the production and sale of cannabis for recreational and medical use has been associated with an increase in the potency of cannabinoid products, use rates, and the prevalence of cannabis use disorder.

• Greater accessibility to cannabis has also been linked to higher rates of traffic accidents, and frequent use is associated with a higher risk of hyperemesis syndrome and cardiovascular disease.

• Meta-analytic evidence indicates that the short-term effects of cannabis include decreases in cognitive performance, but these reductions may not persist after 72 hours of abstinence.

• Given the disruption of the endocannabinoid system by tetrahydrocannabinol (THC), brain regions with high density of cannabinoid receptors 1 (CB1) can be altered by cannabis use.

Methodology

• Researchers analyzed data from 1,003 young adults (mean age 28.7 years; 46.9% men) with magnetic resonance imaging, urinary toxicology, and data on cannabis use from the Human Connectome Project, collected between August 2012 and 2015.

• Participants were classified as heavy users (>1,000 uses, n=88), moderate (10-999 uses, n=179), or non-users (<10 uses, n=736) of cannabis, based on the Semi-Structured Assessment for the Genetics of Alcoholism.

• Brain activation was assessed during seven distinct tasks administered during the functional MRI session, including working memory, reward, emotion, language, motor function, relational assessment, and theory of mind.

A linear mixed-effects regression model was used to examine the association between lifetime history of cannabis use and recent use, with the mean value of brain activation on each task. Key Information Lifetime heavy cannabis use was significantly associated with lower activation during the working memory task (Cohen's d, -0.28; 95% confidence interval, -0.5 to -0.06; P = 0.02), with more pronounced effects on the anterior insula, medial prefrontal cortex, and dorsolateral prefrontal cortex. The association between heavy cannabis use and lower brain activation during the working memory task remained significant even after excluding individuals with recent cannabis use. Recent cannabis use was associated with lower performance and lower brain activation in working and motor memory tasks, although these associations did not remain significant after correcting for false discovery rate. No other task demonstrated a significant association with a history of heavy use, recent use, or diagnosis of cannabis dependence. In practice These results suggest that cannabis use is associated with both short- and long-term brain function outcomes, especially during working memory tasks. These findings identify "negative outcomes associated with lifetime heavy cannabis use and working memory in healthy young adults that may be long-lasting," the study authors wrote. The most affected brain regions have a relatively high density of CB1 receptors and constitute the area where receptor availability has been found reduced in association with daily exposure to cannabis. Similarly, studies in rodents have shown that exposure to THC reduced the density and sensitivity of CB1 receptors in these brain regions, providing evidence that heavy cannabis use can cause neural adaptation. This reduction mechanism could explain the findings that cannabis use is associated with lower cortical thickness in the dorsomedial and dorsolateral prefrontal cortex

Source

The study was led by Joshua L. Gowin, PhD, of the Department of Radiology at the University of Colorado's Anschutz Medical Campus. It was published online on January 28 in JAMA Network Open.

 Limitations

This was an uncontrolled cross-sectional study, so the observed associations between cannabis and brain function outcomes should not be considered causal. The participants were young adults, so these findings may not be generalizable to other age groups. History of heavy cannabis use was defined as more than 1,000 uses or diagnosis of cannabis dependence, but the sample was recruited from the community, which may represent a relatively low level of severity of dependence. Data were lacking to determine when the most recent use occurred or to quantify the concentration of THC metabolites.The study was supported by grants from the U.S. National Institutes of Health (NIH) and funded by 16 NIH institutes and centers that support NIH Blueprint Neuroscience Research. The study also received support from the McDonnell Center for Systems Neuroscience at the University of Washington and grants DAO54212, DA054096, and DA056408 from the National Institute on Drug Abuse.