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Marijuana and the Developing Brain


You can’t get away from it, the big marijuana debate here in the US. Is it good? Is it bad? What are other countries doing? There are also a lot of claims made about marijuana, most of which aren’t true, namely the big medical claims. Then there is the other side of that fence, what about some of the health issues that are claimed, where does science sit on that?

Well as might be expected, like any drug, marijuana isn’t without risks.  Using marijuana frequently can have a significant negative effect on the still developing brains of teenagers and young adults, including cognitive decline, poor attention and memory, and decreased IQ. It should be mentioned that brain growth and development has been shown to last until the mid-twenties, one reason why I personally think the drinking age should be raised. That is a whole other topic though.

“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, a huge increase from the 2.4 percent in 1993. This is probably due to larger social acceptance in teens and young adults who are increasingly exposed to in through the media and pop-culture.

Additionally, 31 percent of young adults [defined as 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, which was reference to a 2012 longitudinal study of 1,037 participants who were followed from birth to age 38.

It doesn’t stop there, brain imaging studies of regular marijuana users have shown significant changes in their brain structure, particularly and maybe unsurprisingly 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 have increased their marijuana use in the past year, she said. These findings held true even after researchers controlled for major medical conditions, prenatal drug exposure, developmental delays and even 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 the chemical THC than other strains, said Alan Budney, PhD, of Dartmouth College. For those who don’t know, THC is responsible for most of marijuana’s psychological effects. Research has shown that frequent use of high potency THC can increase the 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.

So while acceptance has increased, it should still be known that children and young adults should not be using any sort of drugs, including marijuana. The effects on the developing brain have been documented and while I don’t want to get into if it should be legal or not, I will say that I think at the very least it needs to be more tightly regulated. Then again I feel the same way about tobacco and alcohol, so at least I am consistent with my views.

Sources (in Quantum Mechanical or random, order)
Giedd JN, Blumenthal J, Jeffries NO, Rajapakse JC, Vaituzis AC, Liu H, Berry YC, Tobin M, Nelson J, & Castellanos FX (1999). Development of the human corpus callosum during childhood and adolescence: a longitudinal MRI study. Progress in neuro-psychopharmacology & biological psychiatry, 23 (4), 571-88 PMID: 10390717

Giedd, J. N (2004). Structural magnetic resonance imaging of the adolescent brain Adolescent Brain Development: Vulnerabilities and Opportunities

Giedd, J. N., J. Blumenthal, et al (1999). Brain development during childhood and
adolescence: A longitudinal MRI study Nature Neuroscience

Friese B, & Grube JW (2013). Legalization of medical marijuana and marijuana use among youths. Drugs (Abingdon, England), 20 (1), 33-39 PMID: 23641127

Chadwick B, Miller ML, & Hurd YL (2013). Cannabis Use during Adolescent Development: Susceptibility to Psychiatric Illness. Frontiers in psychiatry, 4 PMID: 24133461

Lisdahl, K., Wright, N., Medina-Kirchner, C., Maple, K., & Shollenbarger, S. (2014). Considering Cannabis: The Effects of Regular Cannabis Use on Neurocognition in Adolescents and Young Adults Current Addiction Reports, 1 (2), 144-156 DOI: 10.1007/s40429-014-0019-6

Choo EK, Benz M, Zaller N, Warren O, Rising KL, & McConnell KJ (2014). The impact of state medical marijuana legislation on adolescent marijuana use. The Journal of adolescent health : official publication of the Society for Adolescent Medicine, 55 (2), 160-6 PMID: 24742758

Joffe A, American Academy of Pediatrics Committee on Substance Abuse, & American Academy of Pediatrics Committee on Adolescence (2004). Legalization of marijuana: potential impact on youth. Pediatrics, 113 (6), 1825-6 PMID: 15173518

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