Categories
BLOG

if i smoke weed once a week

How Casual Marijuana Can Cause Brain Abnormalities

Steven Gans, MD is board-certified in psychiatry and is an active supervisor, teacher, and mentor at Massachusetts General Hospital.

PhotoAlto/Katarina Sundelin/Getty Images

Even casual, recreational use of marijuana by young people can affect the regions of the brain involved in emotion, motivation, and decision-making. Scientists say that they now have the evidence to prove it.  

A review of studies on the functional and morphological impact of marijuana use on the brain shows changes in three areas. These include the prefrontal cortex, amygdala and hippocampus.   The differences in brain abnormalities compared to non-smokers is directly related to how much marijuana is consumed, the researchers found.

Studies of Heavy Marijuana Smokers

There have been many previous studies that have linked marijuana use to impairment in motivation, attention, learning, and memory. Studies have found that long-time marijuana use can hamper motivation. Other studies have linked marijuana use to impaired learning and social skills.

Other research has found that smoking marijuana can impair the ability to maintain attention and another study found that early marijuana use can cause cognitive impairment not seen in those who begin smoking marijuana later in life.  

Research on the Effect of Occasional Marijuana Use

The difficulty is that most, if not all, of the previous studies on the subject involved chronic, heavy marijuana smokers.

A study published in The Journal of Neuroscience was the first to link casual, occasional marijuana use with negative effects on the brain.

Although the sample size of the study was small (only 40 total subjects, including 20 non-marijuana using controls) the differences in the brains of the two groups were remarkable, the authors reported.  

Researchers at Northwestern University and Massachusetts General Hospital/Harvard Medical School used magnetic resonance imaging to compare the brains of 20 young people who reported smoking marijuana at least once per week with 20 others age 18-25 who reported little to no history of marijuana use.

The scientists measured the volume, shape, and density of grey matter in the nucleus accumbens and the amygdala. The nucleus accumbens is involved in reward processing and decision making, while the amygdala is associated with emotion.

The participants were screened to determine that none were dependent upon marijuana or any other drugs and none of the participants had ever abused any other drugs.

Those who used marijuana were asked to estimate their marijuana consumption over a three-month period, including the number of days they smoked and the amount of the drug consumed each day.

Effects of Marijuana on the Size, Shape, and Density of the Brain

The researchers found that the more the marijuana users reported consuming, the greater the abnormalities in the nucleus accumbens and the amygdala on the MRI images.   The shape and density of both regions of the brain were also different between marijuana users and non-users.

The study revealed that the brains of those who smoked only one joint a day or those who smoked only once a week were changed.

“This study raises a strong challenge to the idea that casual marijuana use isn’t associated with bad consequences,” said Hans Breiter, M.D. one of the study’s authors. “Some of these people only used marijuana to get high once or twice a week,”

Why Occasional Marijuana Use Can Cause Problems

“People think a little recreational use shouldn’t cause a problem if someone is doing OK with work or school. Our data directly says this is not the case,” Breiter said in a news release.  

Other researchers, not involved in the Massachusetts General study, agreed that finding changes in the brains of casual marijuana users was surprising.

“This study suggests that even light to moderate recreational marijuana use can cause changes in brain anatomy,” said Carl Lupica, Ph.D., of the National Institute on Drug Abuse. “These observations are particularly interesting because previous studies have focused primarily on the brains of heavy marijuana smokers, and have largely ignored the brains of casual users.”

The research was funded by the National Institute on Drug Abuse, the Office of National Drug Control Policy, Counterdrug Technology Assessment Center, and the National Institute of Neurological Disorders and Stroke.

Has smoking marijuana become a problem for you? Take the Marijuana Screening Quiz.

Learn about studies that show even casual marijuana use can cause significant changes in brain regions associated with motivation and decision-making.

Experts Explain What Happens In Your Body If You Smoke Weed Daily, Weekly, Or Monthly

It’s not as cut & dry as you learned in D.A.R.E.

Sometimes picking up a joint can seem like the best way to wind down (particularly if you live in a place where it’s legal) — but you might be wondering what cannabis does to your body over time. It’s a complex plant, and its impact on your health is still being studied, with decades of legal restrictions slowly lifting.

Pot has been found to have more health benefits over the last few years, like alleviating chronic pain and helping insomnia. But depending on how often you smoke, there could be risks, too.

“Work from my lab and others does suggest that frequency of use correlates positively with cannabis-related problems,” Mitchell Earleywine Ph.D., professor of psychology at the University of Albany, tells Bustle. “But the effect isn’t particularly big.” Your experience will be pretty different if you’re an occasional weed-brownie-haver as opposed to a several-times-a-day vaper.

Whether you identify as an occasional or daily user, a bong ripper, or gummy-snacker, here’s what’s happening in your body when you use weed.

Occasional Use

Scientists are still trying to figure out how many of weed’s effects are temporary, what’s long-term, and how much dosage is required. (And then there’s the fact that men react differently to women when it comes to cannabinoids, which is often not used as a factor in studies.) “Occasional use by adults is generally safe, particularly for those who use the vaporizer,” Earleywine says.

One way a smoking session every few months may hurt your body is in immune response. There is evidence cannabinoids interferes in our resistance to infection. One study in Journal of Cannabis Research in 2020 found that heavy cannabis use — defined as seven or more hits in the past 30 days — tended to increase white blood cells, which indicates that the immune system is under strain, but it’s not clear if occasional use will have the same effects.

A single hit will significantly impair your balance, your reaction time, and your ability to form new memories, but these effects will wear off as your high does. “The impairment from cannabis relates to impaired ability to deal with unexpected events, like avoiding a car that comes out of nowhere,” Matthew W. Johnson, Ph.D., professor of psychiatry at Johns Hopkins University School of Medicine, tells Bustle. And 2015 study in Schizophrenia Bulletin has found that just one hit can cause paranoia in some people, which you probably knew.

Monthly Use

Determining whether risks increase with use when it comes to cannabis is a bit tricky. “Monthly use has no meaningful impact,” Jonathan Caukins Ph.D., professor of operations research and public policy at Carnegie Mellon University’s Heinz College and an expert on cannabis legalization, tells Bustle.

Having a monthly smoke may to be linked to temporary harm to cognitive skills like memory, assimilation of new information, and attention, but it’s likely to be pass pretty quickly. According to a review of studies published in Journal of Addiction Medicine in 2012, a monthly user will “spring back” from this damage over four weeks of abstinence.

One study, published in 2014 by the Society Of Prevention Research, looked at boys throughout their lives, from 7th grade to age 35. Monthly weed use was common, and it didn’t seem to make a difference to the 35-year-olds’ health issues, medications, injuries, or hospitalizations. Men who didn’t smoke weed had the same outcomes.

Weekly Use

When you smoke weekly, health risks go up. A 2020 study of 3,400 people published in JACC Cardiovascular Imaging found that weekly users showed problems with the left ventricles of their hearts and shifts in their heart structure. Regular use has also been linked to an increased risk of heart attacks, particularly in the first few hours after a session.

A 2011 review of weekly users, published in Indian Journal of Psychiatry, found that going cold turkey for a month can restore cognitive powers, from reaction time to memory and dexterity. Other studies, though, only showed partial recovery. The Canadian Centre on Substance Abuse & Addiction did a roundup of studies in 2019 that found weekly smoking was much less likely to produce permanent cognitive problems than daily smoking.

For all the fearmongering, even daily use of weed isn’t going to be that harmful, all things considered. A 2015 study published in Annals of the American Thoracic Society stated fairly definitively that, even after 20 years of daily use, weed smokers were still able to expel the same amount of air from their lungs as non-smokers.

The scientific opinion on daily smoking and lung cancer isn’t clear either. Cancer Research UK found that some studies believe there is a link, while others don’t believe the indications are strong enough. They point out that the huge variation in the strength of weed, the fact that people sometimes smoke it with tobacco, and the different ways individuals process it all make a link hard to pin down. “Although cannabis does increase symptoms of bronchitis like coughing and wheezing, it does not appear to elevate risk for lung cancer,” Earleywine says.

There’s an argument that daily, heavy spliff use may actually alter the structure of your brain. “Daily use has many dangers, including most obviously altering brain pathways,” Caukins says. A 2014 study published in PNAS found that daily users seemed to have a smaller orbitofrontal cortex, the part of the brain that helps with emotional and decision-oriented processing, but also had denser links between different parts of the brain. A 2017 study published in Pediatric Neurology also found that chronic weed use was linked to damage in the brain’s white matter.

“One effect is subtle memory deficits,” Johnson says. “These seems to disappear with about a month of abstinence.” Daily use can also result in dependence, he says, which means you start feeling irritable, sleepless and lose your appetite whenever you stop.

The Bottom Line

“The data on cannabis and altered brain structure only seem to appear in those who used the plant heavily while still very young,” Earleywine cautions. And these findings have been hard to replicate. “Plenty of daily users have literally no problems related to the plant, and some occasional users consume in unsafe ways,” he says. “Those who begin use early in life tend to show more problems with the plant than those who start when they are older.”

So frequency may not be the be-all and end-all for determining how weed is affecting your health; what time of day you smoke, how you do it, and how young you were when you began smoking are all factors, too.

Readers should note that laws governing cannabis, hemp and CBD are evolving, as is information about the efficacy and safety of those substances. As such, the information contained in this post should not be construed as legal or medical advice. Always consult your physician prior to trying any substance or supplement.

Jonathan Caukins Ph.D.

Mitchell Earleywine Ph.D.

Matthew W. Johnson, Ph.D.

Alshaarawy, O. (2019) Total and differential white blood cell count in cannabis users: results from the cross-sectional National Health and Nutrition Examination Survey, 2005–2016. J Cannabis Res1, 6. https://doi.org/10.1186/s42238-019-0007-8

Crean, R. D., Crane, N. A., & Mason, B. J. (2011). An evidence based review of acute and long-term effects of cannabis use on executive cognitive functions. Journal of addiction medicine, 5(1), 1–8. https://doi.org/10.1097/ADM.0b013e31820c23fa

Hall W. (2015). What has research over the past two decades revealed about the adverse health effects of recreational cannabis use?. Addiction (Abingdon, England), 110(1), 19–35. https://doi.org/10.1111/add.12703

Filbey, F. M., Aslan, S., Calhoun, V. D., Spence, J. S., Damaraju, E., Caprihan, A., & Segall, J. (2014). Long-term effects of marijuana use on the brain. Proceedings of the National Academy of Sciences of the United States of America, 111(47), 16913–16918. https://doi.org/10.1073/pnas.1415297111

Freeman, D., Dunn, G., Murray, R. M., Evans, N., Lister, R., Antley, A., Slater, M., Godlewska, B., Cornish, R., Williams, J., Di Simplicio, M., Igoumenou, A., Brenneisen, R., Tunbridge, E. M., Harrison, P. J., Harmer, C. J., Cowen, P., & Morrison, P. D. (2015). How cannabis causes paranoia: using the intravenous administration of ∆9-tetrahydrocannabinol (THC) to identify key cognitive mechanisms leading to paranoia. Schizophrenia bulletin, 41(2), 391–399. https://doi.org/10.1093/schbul/sbu098

Kempker, J. A., Honig, E. G., & Martin, G. S. (2015). The effects of marijuana exposure on expiratory airflow. A study of adults who participated in the U.S. National Health and Nutrition Examination Study. Annals of the American Thoracic Society, 12(2), 135–141. https://doi.org/10.1513/AnnalsATS.201407-333OC

Khanji, M. Y., Jensen, M. T., Kenawy, A. A., Raisi-Estabragh, Z., Paiva, J. M., Aung, N., Fung, K., Lukaschuk, E., Zemrak, F., Lee, A. M., Barutcu, A., Maclean, E., Cooper, J., Piechnik, S. K., Neubauer, S., & Petersen, S. E. (2020). Association Between Recreational Cannabis Use and Cardiac Structure and Function. JACC. Cardiovascular imaging, 13(3), 886–888. https://doi.org/10.1016/j.jcmg.2019.10.012

Mandelbaum, D. E., & de la Monte, S. M. (2017). Adverse Structural and Functional Effects of Marijuana on the Brain: Evidence Reviewed. Pediatric neurology, 66, 12–20. https://doi.org/10.1016/j.pediatrneurol.2016.09.004

Shrivastava, A., Johnston, M., & Tsuang, M. (2011). Cannabis use and cognitive dysfunction. Indian journal of psychiatry, 53(3), 187–191. https://doi.org/10.4103/0019-5545.86796

Struik, D., Sanna, F., & Fattore, L. (2018). The Modulating Role of Sex and Anabolic-Androgenic Steroid Hormones in Cannabinoid Sensitivity. Frontiers in behavioral neuroscience, 12, 249. https://doi.org/10.3389/fnbeh.2018.00249

National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Population Health and Public Health Practice; Committee on the Health Effects of Marijuana: An Evidence Review and Research Agenda. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. Washington (DC): National Academies Press (US); 2017 Jan 12. 8, Immunity.

This article was originally published on April 20, 2016

Cannabis’ impact on your health is still being studied, with decades of legal restrictions slowly lifting.