• Home
  • Store
    • Newsletter Subscriptions
    • Multimedia
    • Books
    • eBooks
    • ABPN SA Courses
    • Social Work Courses
  • CME Center
  • Multimedia
    • Podcast
    • Webinars
    • Blog
    • Psychiatry News Videos
    • Medication Guide Videos
  • Newsletters
    • General Psychiatry
    • Child Psychiatry
    • Addiction Treatment
    • Hospital Psychiatry
    • Geriatric Psychiatry
    • Psychotherapy and Social Work
  • FAQs
  • Med Fact Book App
  • Log In
  • Register
  • Welcome
  • Sign Out
  • Subscribe
Home » Marijuana May Hurt Cognitive Function, Worse with Heavier Use

Marijuana May Hurt Cognitive Function, Worse with Heavier Use

October 1, 2012
Glen Spielmans, PhD
From The Carlat Psychiatry Report
Issue Links: Learning Objectives | Editorial Information | PDF of Issue
Glen Spielmans, PhD Associate professor of psychology, Metropolitan State University, St. Paul, MN Glen Spielmans, PhD, has disclosed that he has no relevant financial or other interests in any commercial companies pertaining to this educational activity.

Subject:
Substance Abuse

Short Description:
Marijuana May Hurt Cognitive Function, Worse with Heavier Use

Background:

Does marijuana affect cognitive function? There seems to be no shortage of opinions on this question, but no prospective, longitudinal study has ever been published. Until now, that is. Researchers in New Zealand followed more than 1,000 subjects from their birth in 1972–1973 until age 38, to ask whether regular cannabis users showed any evidence of cognitive decline.

The answer, surprisingly (or not, depending on where you stand on the issue), was a resounding “yes.” Studying the 1,037 individuals in the famous Dunedin Study, researchers found that those who were dependent on cannabis, or even who used it regularly, experienced an overall decrease in IQ. Moreover, the extent of decline was correlated with heavier cannabis use. Those who admitted to regular cannabis use on more than three follow-up assessments in the 38-year period, for example, lost an average of six IQ points (99.68 to 93.93) between age 13 and age 38, while those who reported it only once lost only one point. Non-users actually gained an IQ point. Decline was apparent in multiple cognitive domains, including executive function, memory, processing speed, and verbal comprehension, and again, performance was worse with heavier use.

The researchers performed multiple controls. They eliminated those with other drug or alcohol dependence, or schizophrenia, and they even controlled for years of education. With each analysis, the same trend held true, and was statistically significant. They even interviewed informants (people “who knew the subjects well”), and these independent observers noticed more attention and memory problems among subjects with heavier cannabis use. Perhaps most notably, the subset of users who were diagnosed with cannabis dependence before age 18 lost IQ points (as many as eight), while adult-onset cannabis users experienced no such decline (Meier MH et al, Proc Natl Acad Sci USA 2012, online ahead of print).

TCPR's Take:
This was an impressive study, not only for the consistency of its findings, but for its scope, involving more than 1,000 subjects followed at regular intervals over 38 years. The study may have been limited by underreporting of drug use or the lack of objective drug-use data (like urine samples), and it should not be interpreted as proof that cannabis use causes cognitive impairment. Nonetheless, the observations that IQ loss was most concentrated in those who started using in adolescence, and the extent of loss was correlated with heavier cannabis use, argue in favor of potentially detrimental effects of cannabis on the developing brain. If you’re looking for evidence to convince your younger patients that marijuana use may predict lower IQ in adulthood, look no further.
General Psychiatry
KEYWORDS research_updates substance-abuse
    Ccpr octnovdec2020 qa1 headshot spielmans 150x150
    Glen Spielmans, PhD

    L-Methylfolate May Offer Modest Boost to Antidepressants

    More from this author
    www.thecarlatreport.com
    Issue Date: October 1, 2012
    SUBSCRIBE NOW
    Table Of Contents
    Do Devices Work for Depression?
    Neuroimaging of Mood Disorders
    ECT Still Alive and Well
    Marijuana May Hurt Cognitive Function, Worse with Heavier Use
    Anti-Inflammatory Drug an Antidepressant?
    DOWNLOAD NOW
    Featured Book
    • MFB7e_Print_App_Access.png

      Medication Fact Book for Psychiatric Practice, Seventh Edition (2024) - Regular Bound Book

      The updated 2024 reference guide covering the most commonly prescribed medications in psychiatry.
      READ MORE
    Featured Video
    • KarXT (Cobenfy)_ The Breakthrough Antipsychotic That Could Change Everything.jpg
      General Psychiatry

      KarXT (Cobenfy): The Breakthrough Antipsychotic That Could Change Everything

      Read More
    Featured Podcast
    • shutterstock_2622607431.jpg
      General Psychiatry

      Should You Test MTHFR?

      MTHFR is a...
      Listen now
    Recommended
    • Join Our Writing Team

      July 18, 2024
      WriteForUs.png
    • Insights About a Rare Transmissible Form of Alzheimer's Disease

      February 9, 2024
      shutterstock_2417738561_PeopleImages.com_Yuri A.png
    • How to Fulfill the DEA's One Time, 8-Hour Training Requirement for Registered Practitioners

      May 24, 2024
      DEA_Checkbox.png
    • Join Our Writing Team

      July 18, 2024
      WriteForUs.png
    • Insights About a Rare Transmissible Form of Alzheimer's Disease

      February 9, 2024
      shutterstock_2417738561_PeopleImages.com_Yuri A.png
    • How to Fulfill the DEA's One Time, 8-Hour Training Requirement for Registered Practitioners

      May 24, 2024
      DEA_Checkbox.png
    • Join Our Writing Team

      July 18, 2024
      WriteForUs.png
    • Insights About a Rare Transmissible Form of Alzheimer's Disease

      February 9, 2024
      shutterstock_2417738561_PeopleImages.com_Yuri A.png
    • How to Fulfill the DEA's One Time, 8-Hour Training Requirement for Registered Practitioners

      May 24, 2024
      DEA_Checkbox.png

    About

    • About Us
    • CME Center
    • FAQ
    • Contact Us

    Shop Online

    • Newsletters
    • Multimedia Subscriptions
    • Books
    • eBooks
    • ABPN Self-Assessment Courses

    Newsletters

    • The Carlat Psychiatry Report
    • The Carlat Child Psychiatry Report
    • The Carlat Addiction Treatment Report
    • The Carlat Hospital Psychiatry Report
    • The Carlat Geriatric Psychiatry Report
    • The Carlat Psychotherapy Report

    Contact

    carlat@thecarlatreport.com

    866-348-9279

    PO Box 626, Newburyport MA 01950

    Follow Us

    Please see our Terms and Conditions, Privacy Policy, Subscription Agreement, Use of Cookies, and Hardware/Software Requirements to view our website.

    © 2025 Carlat Publishing, LLC and Affiliates, All Rights Reserved.