Casual marijuana use may damage your brain
April 16th, 2014
09:02 AM ET

Casual marijuana use may damage your brain

If you thought smoking a joint occasionally was OK, a new study released Tuesday suggests you might want to reconsider.

The study, published in the Journal of Neuroscience, is the first to link casual marijuana use to major changes in the brain. And according to the researchers, the degree of abnormalities is based on the number of joints you smoke in a week.

Using different types of neuroimaging, researchers examined the brains of 40 young adults between the ages of 18 and 25 who were enrolled in Boston-area colleges. Twenty of them smoked marijuana at least once a week. The other 20 did not use pot at all.

The marijuana smokers were asked to track their cannabis use for 90 days. All were given high-resolution MRIs, and users and non-users' results were compared.

Researchers examined regions of the brain involved in emotional processing, motivation and reward, called the nucleus accumbens and the amygdala.  They analyzed volume, shape and density of grey matter - where most cells in brain tissue are located.

"I think the findings that there are observable differences in brain structure with marijuana even in these young adult recreational users indicate that there are significant effects of marijuana on the brain," says Dr. Jodi Gilman, lead author and a researcher in the Massachusetts General Center for Addiction Medicine. "Those differences were exposure-dependent, meaning those who used more marijuana had greater abnormalities."

More than a third of the group - seven of the 20 - only used pot recreationally once or twice a week. The median use was six joints a week, but there were four people who said they smoked more than 20 joints a week. None of the users reported any problems with school, work, legal issues, parents or relationships, according to Dr. Hans Breiter, co-senior author of the study and a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine.

"There's a general idea out there that casual use of marijuana does not lead to bad effects, so we started out to investigate that very directly," Breiter said. "This research with the other studies we have done have led me to be extremely concerned about the effects of marijuana in adolescents and young adults and to consider that we may need to be very careful about legalization policies and possibly consider how to prevent anyone under age 25 to 30 from using marijuana at all."

Researchers have long been concerned about the effects of marijuana on the developing brain - teens and adolescents under the age of 25. Preliminary research has shown that early onset smokers are slower at tasks, have lower IQs later in life and even have a higher risk of stroke.

Dr. Staci Gruber, director of the Cognitive and Clinical Neuroimaging Core at McLean Hospital in Boston and a professor of psychiatry at Harvard Medical School, has conducted numerous studies on marijuana use and brain function.

"This data certainly confirms what others have reported with regard to changes in brain structure," she said. "When we consider the findings of the Gilman ... study with our own and other investigations of marijuana use, it's clear that further investigation is warranted, specifically for individuals in emerging adulthood, as exposure during a period of developmental vulnerability may result in neurophysiologic changes which may have long-term implications."

Gruber says we need to take a closer look at all pot users whether they smoke once or twice a week or four or time times a week.

And she had this advice for adolescents: "Don't do it early–prior to age 16. That's what our data suggests, that regular use of marijuana prior to age 16 is associated with greater difficulty of tasks requiring judgment, planning and inhibitory function as well as changes in brain function and white matter microstructure relative to those who start later."

According to the National Survey on Drug Use and Health, in 2012 nearly 19 million Americans used marijuana. It's the most-used illegal drug in the country and use is increasing among teenagers and young adults.

Results of the new study match those of animal studies, authors say, showing that when rats are given tetrahydrocannabinol, or THC - the ingredient in marijuana the gets you high - their brains rewire and new connections are formed.

Gilman thinks when people start to become addicted to substances, their brains form these new connections too.

"The next important thing to investigate is how these structural abnormalities relate to functional outcomes," she said. "Currently we don't know how much marijuana is safe and I think this study shows that we should be cautious about marijuana use in adolescents and young adults whose developing brain may be even more susceptible to cannabis-induced changes."

soundoff (765 Responses)
  1. Julie Rambow

    To clarify a bit more, using marijuana moderately, (1 oz/mo), or heavily, (2-3 oz/mo), will cause serious structural and neurological changes. This is why they say only use it for medical purposes as needed. If used moderately or heavily it will leave large holds in the prefrontal cortex areas, (larger than any other drug). The prefrontal cortex controls: Attention span, judgement, impulses, organization/procrastination, forward thinking, internal supervision, and empathy/insight (needing left and right brain communication). A spect scan will show the "holes" that are not getting circulation. The brain will heal itself through therapy or meds, but not much. The worst symptoms, which greatly affects the social life, work, and driving skills, is the paranoia, ADD, and slow response times.

    January 12, 2015 at 06:05 | Report abuse | Reply
  2. Dmoney

    This lady is just trying to paint a negative picture to maintain the business she is in – "Addiction medicine"

    April 16, 2015 at 16:00 | Report abuse | Reply
  3. harold

    I been smoking since I was eight years old and I'm 46 years old and there is nothing wrong with me I'm still a healthy man and it's been helping me with my muscle spasm and all my chronic pain and I do not take pills anymore because all they did was make me sick and stayed in bed all day

    April 19, 2015 at 21:38 | Report abuse | Reply
    • Matt

      You also said "I been" and incorrectly used the singular form of "spasm," not to mention your incredibly long, unpunctuated run-on sentence.

      May 4, 2015 at 17:45 | Report abuse |
    • B

      Your post would indicate otherwise. Have you had your brain scanned lately, Harold?

      March 21, 2017 at 07:14 | Report abuse |
  4. asics singapore online

    asics running shoes
    asics singapore online http://www.dardenplannedgiving.org/

    April 29, 2015 at 03:10 | Report abuse | Reply
  5. Jolynn Schmiege

    even get started.


    December 3, 2015 at 21:02 | Report abuse | Reply
  6. Eugene Frietas

    T?ank you s? much! This is definitely an ?onderful internet site!


    December 3, 2015 at 21:03 | Report abuse | Reply
  7. Weldon Brezina

    overnight pet sitting


    August 3, 2016 at 11:22 | Report abuse | Reply
  8. Latrisha Yasurek

    water ionizers


    September 11, 2016 at 17:06 | Report abuse | Reply
  9. Alverta Mcnany

    Calgary roofer


    September 29, 2016 at 11:00 | Report abuse | Reply
  10. subohmcell battery

    Great place to try out e-cigs if you've been thinking about making the switch from regular cigs. Sub ohm cell battery Websites “the owner" answered every question I had about e-cigs and never once did I feel rushed to make a decision to purchase. Would gladly recommend this place and definitely go back again...subohmcell battery 18650

    October 14, 2016 at 06:44 | Report abuse | Reply
  11. Delhi call Girl Sevices

    It’s truly a nice and useful piece of information. I’m glad that you just shared this useful information with us. Please stay us up to date like this. Thank you for sharing.


    December 8, 2016 at 02:36 | Report abuse | Reply
  12. Om Sai Household Switching

    After study a couple of of the weblog posts on your website now, and I actually like your approach of blogging. I bookmarked it to my bookmark web site list and might be checking back soon. Pls check out my website as nicely and let me know what you think.


    January 8, 2017 at 04:23 | Report abuse | Reply
  13. Om sai Packers Movers

    I was wondering if you ever considered changing the structure of your website? Its very well written; I love what youve got to say. But maybe you could a little more in the way of content so people could connect with it better. Youve got an awful lot of text for only having one or 2 images. Maybe you could space it out better?


    January 8, 2017 at 04:50 | Report abuse | Reply
  14. poker online terpercaya

    grand central stations are really built with some great architectural design, they are very impressive.,


    January 18, 2017 at 04:57 | Report abuse | Reply
  15. Roosevelt Rieker

    That is the best search system in the planet


    April 17, 2017 at 10:04 | Report abuse | Reply
  16. Monopoly e-liquid

    Great post. Your post basically got me thinking of launching my own small business. Has anyone here happened upon find a vape supplier com? It is simply speaking a revolutionary marketplace for vape firms. I am thinking about starting an e-liquid line of products (liquid for vaporizers) but rather than spending funds into a web site, hosting, search engine optimization and marketing communications, I am thinking about listing with find a vape supplier com since it permits you to produce your own account and list goods. It is very similar to ebay but it is aimed at businesses. The signing up is free as the platform is in beta edition. Do give me a shout if you have some experience with this website. Would be excellent to hear your ideas.


    April 20, 2017 at 08:56 | Report abuse | Reply
  17. RichardTutt



    Dove Comprare Scarpe Mbt Online
    Adidas Primeknit Calcio
    Skechers Waterproof
    Skechers Shape Ups Memory Foam
    Skechers Australia Boots

    April 25, 2017 at 08:24 | Report abuse | Reply
  18. doudoune ralph lauren femme

    Last season I was always watching behind me and this season is the same.
    doudoune ralph lauren femme http://pl.aasoldes.fr/hacketth-doudoune-Ralph-Lauren-nouveau-style-blue-Doudoune-Ralph-Lauren-Femme-TE2828.html

    September 2, 2017 at 19:00 | Report abuse | Reply
  19. コピーシャネル財布偽物

    フェラーリスーパーコピー,グラハムスーパーコピー,ハリー ウィンストンスーパーコピー,アランシルベスタインスーパーコピー,

    November 2, 2017 at 12:06 | Report abuse | Reply
  20. N級品

    株式会社 スーパーコピーブランド激安市場



    休業日: 365天受付年中無休

    October 10, 2018 at 06:26 | Report abuse | Reply
  21. Randall

    cool stuff man, I myself got some nice cannabis seed at thebuzzfarmer.com , they're super inexpensive there


    August 11, 2019 at 15:28 | Report abuse | Reply
  22. 偽物ブランド時計

    ブランド時計,スーパーコピー 時計,時計 スーパーコピー,ブランド時計N級品
    「ドルチェ&ガッバーナ ベルト」検索結果です。
    楽天市場は、セールや送料 数が日本最大級のインターネット通販サイト・オンラインショッピング コミュニティです。
    (標準順 写真付き一覧)ブランド通販 DOLCE&GABBANAドルチェ&ガッバーナ-ベルトの 商品一覧ページです。
    新作からレアモデルまで、送料無料にて格安通販【スマホにも 対応】 販売中のDOLCE&GABBANAドルチェ&ガッバーナのベルトは、全て自社で 在庫
    スマホで簡単 に出品・購入できるメルカリは、フリマ感覚でドルガバの中古
    偽物ブランド時計 https://www.cocoejp.com/ProductList1.aspx?TypeId=933972618491451

    September 9, 2019 at 20:17 | Report abuse | Reply
  23. Claribel Elva

    Les mouches ne font pas de miel. https://www.cialis20.fr

    December 6, 2019 at 05:17 | Report abuse | Reply
  24. Sherly Natividad

    Per un giorno di gioja, https://www.cialis20.fr I then secure the services of about six in-.

    December 6, 2019 at 05:17 | Report abuse | Reply
  25. Katrin

    Fantastic cbd oil for cats post

    July 9, 2020 at 16:32 | Report abuse | Reply
  26. iwmpmifcls

    Casual marijuana use may damage your brain – The Chart – CNN.com Blogs
    iwmpmifcls http://www.g9a0ao95481p5t0zf7paz1ql5wz2f899s.org/

    November 30, 2020 at 03:31 | Report abuse | Reply
  27. vwdbbkrgik

    Casual marijuana use may damage your brain – The Chart – CNN.com Blogs
    vwdbbkrgik http://www.g9o199kj4c543km38p5uu3oa63ch14ias.org/

    December 4, 2020 at 03:51 | Report abuse | Reply
1 2 3 4 5 6 7 8 9

Leave a Reply to MeMe


CNN welcomes a lively and courteous discussion as long as you follow the Rules of Conduct set forth in our Terms of Service. Comments are not pre-screened before they post. You agree that anything you post may be used, along with your name and profile picture, in accordance with our Privacy Policy and the license you have granted pursuant to our Terms of Service.

About this blog

Get a behind-the-scenes look at the latest stories from CNN Chief Medical Correspondent, Dr. Sanjay Gupta, Senior Medical Correspondent Elizabeth Cohen and the CNN Medical Unit producers. They'll share news and views on health and medical trends - info that will help you take better care of yourself and the people you love.