Effects on Youth
Is marijuana addictive for teens?
Dr. Christine Miller
Yes, 17% of those who began their use in adolescence become addicted, and up to about 50% of
those who become daily users end up with addiction:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4827335/pdf/nihms762992.pdf
Obvious withdrawal symptoms are experienced when heavy users cease their habit:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7146100/
How long the most obvious symptoms of withdrawal last can be found here:
https://pubmed.ncbi.nlm.nih.gov/15514394/
The risk of persisting marijuana use is greater if the product is high in THC concentration:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6991277/
To understand how many teens this may affect, in 2019, 22% were using at least monthly by the
the time they reached 12th grade:
http://www.monitoringthefuture.org/pubs/monographs/mtf-vol1_2019.pdf
And 6.4% were using daily:
https://www.drugabuse.gov/sites/default/files/nida_mtfinfographic2019_fullgraphic.pdf
In the U.S., dependence on marijuana has increased more than dependence on any other drug:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2797098/pdf/ascp-04-1-4.pdf
What are some of the ways in which marijuana influences adolescent brain development?
Dr. Christine Millner
The best studies are those that follow the same individuals over time (longitudinal), so they know
the baseline starting point for each person.
For microstructural effects on white matter in the brain:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4691379/pdf/main.pdf
For effects on brain connectivity:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5963818/pdf/bhw015.pdf
The superior frontal gyrus is thought to be important for higher cognitive functions and working
memory:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6670783/pdf/fpsyt-10-00514.pdf
For the science on IQ decrements:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3479587/pdf/pnas.201206820.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5963818/pdf/bhw015.pdf
and cognitive impairment:
https://ajp.psychiatryonline.org/doi/pdf/10.1176/appi.ajp.2018.18020202
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6821511/pdf/44-6-414.pdf
At what age can the brain be considered fully mature?
Dr. Christine Miller
The late twenties:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6623097/pdf/zns10937.pdf
What are some of the psychological symptoms that adolescents might try to treat with
marijuana, and does it help (e.g. anxiety, depression, ADHD)?
Dr. Christine Miller
The ability of a drug to transiently exert an effect that causes a person to essentially forget about
negative symptoms they are experiencing is important to distinguish from the drug’s long-lasting impact.
As a case in point, it is commonly thought that using marijuana reduces anxiety by making you more relaxed. While that can be a short-term effect, the long-term impact can be quite the opposite:
anxiety or outright panic becomes worse, almost uniformly during intervals between uses
(withdrawal effects):
https://pubmed.ncbi.nlm.nih.gov/12943018/
and in many individuals, even while using:
https://pubmed.ncbi.nlm.nih.gov/17314727/
https://www.sciencedirect.com/science/article/abs/pii/S037687169601277X?via%3Dihub
as confirmed by administering THC in the clinic:
https://pubmed.ncbi.nlm.nih.gov/6285406/
Marijuana use has been shown to double the risk for depression in a rigorous study of twins:
https://pubmed.ncbi.nlm.nih.gov/28750823/
With respect to Attention Deficit Hyperactivity Disorder (ADHD), this may be the sole example of a
well-studied behavioral disorder which generally precedes marijuana use, not vice versa. It is widely acknowledged that ADHD makes substance use of all kinds more likely:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4120046/pdf/nihms592423.pdf
and that the gateway model of drug use is accelerated in those with ADHD:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4180292/
It is worth noting that the stimulant drugs used to treat ADHD may play a role in susceptibility to substance abuse if treatment is commenced in the teens (rather than earlier) as discussed in this review article (“initiation of stimulant medication (methylphenidate in particular) for ADHD during
adolescence may have negative consequences with respect to later SUD”):
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4864167/pdf/nihms774724.pdf
Although rigorous studies of marijuana’s impact on ADHD symptoms are difficult to find in the literature, it has been reported that marijuana-using youth and young adults with ADHD exhibit
more severe symptoms:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3390681/
