Regular marijuana use bad for teens’ brains

Psychology and public health experts weigh in on potential effects of legalization on youth

Frequent marijuana use can have a significant negative effect on the brains of teenagers and young adults, including cognitive decline, poor attention and memory, and decreased IQ, according to psychologists discussing public health implications of marijuana legalization at the American Psychological Association’s 122nd Annual Convention.

“It needs to be emphasized that regular cannabis use, which we consider once a week, is not safe and may result in addiction and neurocognitive damage, especially in youth,” said Krista Lisdahl, PhD, director of the brain imaging and neuropsychology lab at University of Wisconsin-Milwaukee.

Marijuana use is increasing, according to Lisdahl, who pointed to a 2012 study showing that 6.5 percent of high school seniors reported smoking marijuana daily, up from 2.4 percent in 1993. Additionally, 31 percent of young adults (ages 18 to 25) reported using marijuana in the last month. People who have become addicted to marijuana can lose an average of six IQ points by adulthood, according to Lisdahl, referring to a 2012 longitudinal study of 1,037 participants who were followed from birth to age 38.

Brain imaging studies of regular marijuana users have shown significant changes in their brain structure, particularly among adolescents, Lisdahl said. Abnormalities in the brain’s gray matter, which is associated with intelligence, have been found in 16- to 19-year-olds who increased their marijuana use in the past year, she said. These findings remained even after researchers controlled for major medical conditions, prenatal drug exposure, developmental delays and learning disabilities, she added.

“When considering legalization, policymakers need to address ways to prevent easy access to marijuana and provide additional treatment funding for adolescent and young adult users,” she said. She also recommended that legislators consider regulating levels of tetrahydrocannabinol, or THC, the major psychoactive chemical in marijuana, in order to reduce potential neurocognitive effects.

Some legalized forms of marijuana have higher levels of THC than other strains, said Alan Budney, PhD, of Dartmouth College. THC is responsible for most of marijuana’s psychological effects. Some research has shown that frequent use of high potency THC can increase risk of acute and future problems with depression, anxiety and psychosis. “Recent studies suggest that this relationship between marijuana and mental illness may be moderated by how often marijuana is used and potency of the substance,” Budney said. “Unfortunately, much of what we know from earlier research is based on smoking marijuana with much lower doses of THC than are commonly used today.” Current treatments for marijuana addiction among adolescents, such as brief school interventions and outpatient counseling, can be helpful but more research is needed to develop more effective strategies and interventions, he added.

Additionally, people’s acceptance of legalized medical marijuana use appears to have an effect on adolescents’ perception of the drug’s risks, according to Bettina Friese, PhD, of the Pacific Institute for Research and Evaluation in California. She presented results from a 2013 study of 17,482 teenagers in Montana, which found marijuana use among teenagers was higher in counties where larger numbers of people voted to legalize medical marijuana in 2004. In addition, teens in counties with more votes for the legalization of medical marijuana perceived marijuana use to be less risky. The research findings suggest that a more accepting attitude toward medical marijuana may have a greater effect on marijuana use among teens than the actual number of medical marijuana licenses available, Friese said.

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3 thoughts on “Regular marijuana use bad for teens’ brains”

  1. Well, that didn’t take long. I mean for the pro-cannabis acolytes to zoom to the forefront with their patentable brand of religious thinking and rhetoric that they bash on about anytime their global ag commodity of choice is raised as a topic.

    They are like fundamentalist Christians on the topic of religion, or fundamentalist political and social progressives on the topic of IQ: any data that clashes with their orthodoxology gets rejected. There is absolutely no room in their minds for them to be wrong. They have fixed, immutable catechisms of response.

    Fortunately it is no secret that there is nothing more lucrative in human society than the Venn overlap between religion and profit, nor that some of the most profitable religions are entirely secular.

    Unfortunately, a lot of science gets lots in the process, and even more is never allowed to be pursued (for instance, the non-PC types).

    There are very few compelling reasons for anyone ever to tinker with their brain chemistry and biology in such uncontrolled and unscientific ways as cannabis users do. Actually, there are none that I can think of, but cannabis priests always bleat out their fixed talking points on that one. (I’ll save you trouble: CANCER! GLAUCOMA! CHRONIC PAIN!)

    In my 40 years of experience (since my teens) trying to talk to these people, they force someone such as I to concede that the possibility exists that this heavily horticulturally adapted set of plants might have positive uses in certain limited and carefully observed settings. In other words, they push a reasoned person to admit to reasonable open mindedness on a topic about which much more is to be discovered scientifically…and then they use that to return the discussion to their orthodoxy. This is religious behavior, not science.

    But here’s what I care about more than anything: if you, reading this, are a teenager or young adult, and you came to this article with questions or doubts about marijuana, please take that as advice that you have working reason centers. You may not have answers, but you still have the ability to ask questions and dissent from the Baby Boomer’s establishment culture, which has pushed recreational drug use these past 50 years and whose conservatism refuses to consider or allow any other views.

    You will lose nothing by setting the pipe or bong or cookie or vape or whatever aside. All you lose is a badge of succumbing to social pressure carefully engineered by the captains and foot soldiers of an industry valued globally at between $150 and 200 billion.

    Just for a thought experiment, compare that to the global value of McDonald’s sales ($28 billion, according to Forbes). THAT is what is at stake when you or anyone pauses to question cannabis use: people whose sales have three commas and 12 digits.

    At least McDonald’s has made major efforts to listen to organic, sustainable, and whole foods researchers these past 40 years, and adapt their products and indeed entire supply chain, and shape new markets. All cannabis growers and merchants have done is up the THC content and rhetoric.

    I have been watching this week as people mourn the death of American comedian Robin Williams. They are reacting as though the outcome of his life is surprising. Yet there is nothing more predictable than that a Baby Boomer who heavily used cocaine for two decades would have severely scrambled their brain functioning, with vast downstream cognitive, emotional, and behavioral consequences that get called something else (“depression,” etc.).

    In my view the biggest crime of the Baby Boomer social mythology, invented by market researchers and media moguls, was excusing and encouraging drug use, which amounts to an uncontrolled set of self-inflicted neurological experiments. I am a Ph.D. researcher in the biological sciences, my specialty is research design and analysis, my specialty quant. The hoops we have to jump through even to give a survey or simple single-variable test to human subjects are vast in number. But somehow the global cannabis industry can experiment at will on human subjects–and the same people who’d be screaming about human rights in a psychology lab think nothing of exposing subjects to unknown outcomes of these chemical/brain altering socioeconomic experiments.

  2. @Stel1776, completely agree. There really isn’t any validity to this study; I know brilliant people who use cannabis and moronic people who don’t.

    “Drop in IQ”…. please, maybe dumber people are attracted to drugs in general more than others, confounding this study’s results. “No casual relationship*, well of course, that’s understandable – it’s near impossible to infer causation. How would you feel (as a researcher) if you committed yourself to a 38 year longitudinal study (birth – 38) and didn’t come up with significant results (that cannabis is associated with making you dumber)? This study is completely biased.

    Being naïve and ignorant is associated with a narrow minded perspective. Now, I’m not advocating for youth to be using, I think anyone under 18-21 should not be using *legally*. However this study is pure propaganda, and the average non-scientific person will be scared into thinking this is all true. And really, “gray matter”?

    Besides the carcinogenic properties taken in when *smoking* cannabis, and the possible association between THC and psychiatric disorders (cannabis is classified as a hallucinogenic after all), I feel that cannabis is completely safe.

    Use a vaporizer to negate these carcinogenic properties, and using common sense and moderate usage to negate psychosis.

  3. There are a number of concerns about the one Dunedin study [Meier et al. 2012] that found an IQ drop in 19 cannabis users who started in adolescence, continued usage into adulthood, and had 3 or more “dependency” diagnoses. The results of this study have been brought into question in the same journal:

    -Rogeberg O. Correlations between cannabis use and IQ change in the Dunedin cohort are consistent with confounding from socioeconomic status. Proc Natl Acad Sci U S A. 2013.
    -Daly M. Personality may explain the association between cannabis use and neuropsychological impairment. Proc Natl Acad Sci U S A. 2013.
    -Rogeberg O. Reply to Moffitt et al.: Causal inference from observational data remains difficult. Proc Natl Acad Sci U S A. 2013.

    In addition:

    • The authors admitted that, “our data cannot definitively attest to whether this association is causal”.
    • Users only abstained for 1 week. It can take longer for effects to completely wear off in the heaviest of users [Fried. 2005; Pope et al. 2001; Hooper et al. 2014].
    • Abstention from using was not verified by testing (subjects could have still been under the influence).
    • The amount and frequency of cannabis use is largely unknown, therefore “dose dependency” cannot be established.
    • Mental illnesses such as major depression, anxiety, PTSD or traumatic brain injuries were not factored in. Often people self-medicate with cannabis.
    • Out of 1,037 subjects there were only 19 in the group labeled most dependent since adolescence that saw the 8 point drop (not a large sample).
    • There was not a statistically significant change in IQ for cannabis users who used less than 4 days per week.
    • A statistically significant drop in testing scores was not correlated with adult onset usage, even in the most “dependent” group.

    Regardless of the effect of heavy, adolescence onset, long-term cannabis use on IQ, we are not legalizing for teens. Studies have shown that legalized medical cannabis has not caused increased teen use [Choo et al. 2014; Lynne-Landsman et al. 2013; Harper et al. 2012; Anderson et al 2012], nor has decriminalization in Portugal [Hughes & Stevens. 2010].

    Also keep in mind that there is ample evidence that cannabinoids are neuroprotective, even the U.S. government has a patent on them for protecting the brain, Patent #6630507 – Cannabinoids as antioxidants and neuroprotectants.

    Interestingly, teen drinkers who also smoke cannabis may suffer less brain damage than drinkers who do not smoke cannabis:

    “Results confirm previous studies linking adolescent heavy drinking to reduced verbal learning and memory performance. However, this relationship is not seen in adolescents with similar levels of alcohol involvement who also are heavy users of marijuana.”
    Mahmood et al. Learning and memory performances in adolescent users of alcohol and marijuana: interactive effects. J Stud Alcohol Drugs. 2010.

    “Teens reporting binge drinking behaviors alone had significantly lower FA than controls in all eight clusters, whereas teens reporting both binge drinking and marijuana use had lower FA than controls in only three of the eight clusters”
    Jacobus et al. White Matter Integrity in Adolescents with Histories of Marijuana Use and Binge Drinking. Neurotoxicology and Teratology. 2009.

    In this study, researchers observed teens brains over a 1.5 year period. They found that teens who used alcohol during this period had reduced white matter integrity. These changes were not observed in cannabis users:

    “More alcohol use during the interscan interval predicted higher mean diffusivity (i.e., worsened integrity) in right and left superior longitudinal fasciculi, above and beyond baseline values in these bundles. Marijuana use during the interscan interval did not predict change over time.”
    Bava et al. Longitudinal changes in white matter integrity among adolescent substance users. Alcohol Clin Exp Res. 2013.

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