Study: Casual marijuana use may damage your brain

This is an archived article and the information in the article may be outdated. Please look at the time stamp on the story to see when it was last updated.

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."

™ & © 2014 Cable News Network, Inc., a Time Warner Company. All rights reserved.

20 comments

  • dougsmith42

    Smoking weed is supposed to make you a rocket scientist? To each his own. Another irrelevant and misdirected news story. I am now more stupid for reading this.

  • Cloud Lite

    Wonder where they find these individuals to do these “studies” on. I am 27 and I smoke pot every single day and I am COO of an international financial firm, all my close friends that smoke as much as I do are very successful. They are really trying hard to make weed look bad, ha

  • coloradocommish

    Except that the NEW, accepted default, according to Liberals, for determining whether SOMETHING (Anything) is dangerous and should be banned, regulated to save the planet, or is offensive and should be changed, is…. wait for it….whether it affects ONE Person….

    I await your proposed legislation….

  • Gary Hathorn

    More media scare tactics – from a station that says they don’t do that…
    Damage is not the correct word here, alters would be better. There’s no evidence of permanent ‘damage’.

  • Robert Joseph Christiansen

    I have been smoking marijuana since the age of 16. I am now 30. I can tell you right off the bat that, yes, marijuana does ‘alter’ one’s brain function, just as an abundance of oxygen, smoking cigarettes or drinking alcohol can. However, the supposed analysis that individuals who smoke marijuana are slower at tasks and possess a lower IQ is not only unproven, even in a study with a measly 40 people, but preposterous to even suggest. I know a great deal of highly intelligent individuals who are successful in their jobs, their personal lives and are healthy emotionally, mentally and physically, who smoke marijuana every day. Personally, I have a higher performance level than most individuals at my job, and I constantly seek new ways to expand my consciousness and intelligence. While I can agree that one should use caution with anything that affects cognitive thinking, I believe this study serves nothing as an anti-legalization propaganda piece.

  • Gio Navarrete

    Change is not damage, or necessarily bad. The fact is that everything does change our brains. Its called neuroplastisity. Foods and experiences, and things we do change our brain. Take a look at this study or Oreo Cookies:

    http://www.forbes.com/sites/alicegwalton/2013/10/16/why-your-brain-treats-oreos-like-a-drug/

    Note the same regions of the brain are effected. Some people do get addicted to them and to cannabis, but its a mild addiction less severe than to caffeine, and its only like 9% of long term users experience this. What matters is not that some areas of the brain change, but what is the functional translation to behavior?

    From what I’ve seen it makes people better, nicer, and confers many health benefits that are undisputedly positive. Can the same be said for truly deadly and addictive drugs like alcohol and smoking cigarettes? No, and yet its legal. There is a long history of scare tactics and bad science/unfounded conclusions against this herb. It has been a very persecuted herb so when I read studies like this, I tend to be extra critical.

  • Tom Sanders

    Pot has been used for thousands of years and for all that time nothing bad has been associated with it but now that’s it’s legal all of a sudden we have a study that involved 20 people and they say it causes brain changes and now you have every anti pot group using this flawed report (too little people in to short a time to make any conclusion) as gods word…this is why you have excessive regulations on everything…if it fits someone’s political agenda then they use the report as if it’s the final word….if the report consisted of 2 people for 2 days and fit someone’s agenda they use it.

  • Codswallop Hogwash

    Aren’t these comments amazing?
    It is impossible to assess damage to your own brain that occurs slowly over time. You won’t notice the slowing down and other changes.
    Keep these articles coming, KDVR. Some people may pay attention.

  • alphaomega80537

    Here’s a test to see if smoking marijuana causes brain damage: We vote for a Governor this coming November. On one side, there will be John Hickenlooper and on the other side it will most likely be Tom Tancredo.

    John Hickenlooper campaigned against Amendment 64.
    Tom Tancredo supported and still supports Amendment 64.

    Who will the pot smokers vote for? If they vote for Hickenlooper, they have brain damage.

Comments are closed.