Marijuana’s Impact On Brain Function “Minimal,” New Study Says

  • by Paul Armentano, NORML Deputy Director July 28, 2009

    [Editor’s note: This post is excerpted from this week’s forthcoming NORML weekly media advisory. To have NORML’s media advisories delivered straight to your in-box, sign up for NORML’s free e-zine here.]

    The consumption of cannabis, even long-term, has a “minimal” impact on brain function, according to a systematic literature review just published online by the journal Psychological Medicine.

    An international team of investigators from the United Kingdom, Spain, Brazil, Australia, and Switzerland conducted a systematic review of the effects of cannabis on brain structure and function.

    Authors wrote, “We reviewed literature reporting neuroimaging studies of chronic or acute cannabis use published up until January 2009. … Sixty-six studies were identified, of which 41 met the inclusion criteria. Thirty-three were functional (SPECT/PET/fMRI) and eight structural (volumetric/DTI) imaging studies. … Only three of the structural imaging studies found differences between users and controls.”

    Investigators concluded, “Minimal evidence of major effects of cannabis on brain structure has been reported,” noting that marijuana users and controls perform similarly on cognitive tasks.

    According to a 2001 study published in the journal Archives of General Psychiatry, long-term cannabis smokers who abstained from pot for one week “showed virtually no significant differences from control subjects (those who had smoked marijuana less than 50 times in their lives) on a battery of 10 neuropsychological tests.” Investigators added, “Former heavy users, who had consumed little or no cannabis in the three months before testing, [also] showed no significant differences from control subjects on any of these tests on any of the testing days.”

    144 responses to “Marijuana’s Impact On Brain Function “Minimal,” New Study Says”

    1. Let’s get this right folks! Pot smoking affects everyone differently mentally and physically. So how good is this information on testing people who are high vs. those not high?

    2. JAS from NY says:

      About time! All that is needed is for the international community to give our “Czar” the finger and legalize. Our “Government” wont have much left to do besides follow suite or get ready for some serious internal revolts. 20 States already passed legislation to remind the government that they can easily claim soverenty a few more and we will have a good old civil war raging!

      God Bless Americans, to hell with our government!

    3. Ken says:

      I am not surprised at the results. So many people indulge in cannabis without the “dangers” preached by D.A.R.E. and Reefer Madness.
      My question is: How many studies like this will it take to convince the government to stop listing marijuana as a schedule 1 drug?

    4. Nick says:


      More scientific evidence confirming what marijuana users already knew.

      Pot doesn’t make people stupid. Stupid people make people stupid.

    5. adle1984 says:

      the the question is, will our new drug czar Kerlikowske care? chances are, no. but this doesn’t mean all hope is lost friends. our movement cannot be stopped now. it’s only a matter of time before legalization happens. and at that moment, the entire country will ask our government head on: “what the fuck was the point of prohibition?”.

    6. libertine says:

      None of this matters, science doesn’t matter to kerlikowski or any of the other talking heads. Time to take back liberty, it’s unfortunate that no real political change has occurred without violence.(ghandi exception) There are too many wedges driven into america for people to wake up and quit supporting the government with their taxes. They have taken another moral highground with the environment to shield the sheeps eyes from what is important. Remember Reagan and “It’s for the children!”, Environment, Healthcare, Democracy… NO NO NO. Liberty and Republic YES and YES

    7. BusGreg says:

      While not related to this post, CNN’s Wolf Blitzer at 4:40PM Eastern just did a well done report on the legalization efforts in CA. Aside from him opening the segment with putting undo emphasis on “controversial” the segment was unbiased and ended with the mention that CA may legalize as early as next year. It was mentioned about the feds still refusing to even consider medical cannabis.
      Go California and show the rest of the Nation how it is done!

    8. Richard W says:

      Daily, but not chronic use for 6.5 years has resulted in, believe it or not, a statistically significant “increase” in my IQ. However I attribute this to increased emotional stability, which in turn I attribute to cannabis. When I’m feeling better, I function better. This study is old news to me and, I’m guessing, millions of other smokers.

    9. Nick says:

      It pisses me off that the US government keeps lying to its citzens despite these studies. I thought obama was going to embrace science? I guess i justed wasted another one of my votes. Obama is a lier just like everyone else in washington. We need to throw them all out!!!!

    10. Balls Lane says:

      Ummm….DUHHHH! any long time smoker who has ever taken a break, as I have, would tell you exactly the same.

      And we didn’t need all these studies.

      This type of info needsa ot be picked up by major news outlets. The lack of such information in the mass media only perpetuates the misinformation that fuels the drug war.