CMDA's The Point

Vulnerable Brains: Marijuana, Adolescents, and Schizophrenia

May 25, 2023

by Amy Givler, MD

By the time this drops, I will be one week out from age 65. Yet, I’m not grieving—I welcome growing older. Age has its advantages: Fewer emotional roller coasters, for one. For another, I’m better able to articulate my thoughts. And my body hasn’t betrayed me (yet).


However, parts of my brain are proving glitchy, as my memory just isn’t as reliable. I’m trying to humbly believe people when they insist that something happened in a certain way, rather than how I remember it. My math abilities are pathetic. I used to be able to do multiplication and division in my head, and to remember eight-digit numbers. Now even adding and subtracting is best done with paper and pen. I make lists, and I try to remember to look at them.


I want my brain to be functional until my dying day—many years from now, I hope. I’m glad for the brain I have. When I was an adolescent, I had numerous opportunities to ingest mind-altering substances that promised temporary relief from the stress of my circumstances. Only by God’s grace was I able to decline every one of those opportunities.


I’m talking about marijuana. Today, with my glitchy but still functional brain, I am all the more thankful to God that I abstained. The adolescent brain, you see, is damaged by marijuana. I wouldn’t have the brain I have today if I had indulged then.


A recent population-based study in Denmark showed that adolescents with cannabis-use disorder (cannabis is another name for marijuana) have an increased risk for developing schizophrenia. This is much more true for males than females. They estimate there would be one-third fewer cases of schizophrenia in young men if marijuana wasn’t involved.


The association between marijuana use and schizophrenia has been known for more than 30 years, but confirmation studies, and an explanation of the reasons, are just now coming out. U.S. adolescents are using marijuana. In 2019, four out of 10 high school students reported using sometime in their lives, and 22 percent reported using in the last month.


First off, what does marijuana do to that brain? There are two “cannabinoids” in marijuana: THC and CBD. THC is the intoxicating one, and CBD counteracts some of its effects. In the 1970s, these were present in roughly equal percentages, around 2 percent, but street marijuana currently is much higher in THC (and much lower in CBD), at an average of 16 percent, and often much higher.


We have natural cannabinoid receptors in our brains, and we make molecules that connect to those receptors and activate them. Those activated receptors are important for memory, mood and our sensitivity to stress.


A key area of our brains for dealing with emotions is the amygdala, and it is full of these receptors. When all is working properly, the amygdala communicates with the higher brain, the cortex. The cortex interprets the information coming from the amygdala and (most of the time) dampens down the emotional response. Or, in the case of seeing a snake (a creature of which I am phobic-ly fearful), the cortex completely agrees with the panicked response of the amygdala and doesn’t dampen the terror in the slightest.


Which is to say, the amygdala takes the raw emotion of our experiences and sends it to the cortex for proper interpretation.


THC hijacks those cannabinoid receptors, binding to them powerfully. When the amygdala can’t send messages on to the cortex, we are left with raw emotions. The cortex can’t do what it is designed to do, which is to interpret emotions and then dampen them down. THC is well known to increase anxiety, both short-term and long-term. It makes all emotions harder to control.


Cannabinoid receptors are also in many other parts of the brain, and THC interferes with them wherever they are. People under the influence of marijuana tend to look a lot like people who have schizophrenia. Common to both are: racing thoughts, depersonalization, disorganized thinking, hallucinations, delusions and derealization (misperceiving reality so that familiar things seem strange or unreal). The higher the THC concentration, the more altered the perception of reality.


Of course, many users of marijuana are wanting just exactly these effects. The trouble comes when the brain doesn’t return to normal after the high. That is, there are continued episodes of misperceiving reality. The brain can no longer be trusted to correctly interpret what the senses are saying. This is confusing and distressing, and it is more likely to happen in adolescent users rather than adults. Long-term THC exposure can damage the cannabinoid receptors permanently. The higher the THC concentration, the more damage. Two developmental stages are particularly sensitive to damage: 1. the prenatal period, and 2. adolescence.


The number of babies who are being exposed to THC before they are born, when their tiny brains are still developing, is skyrocketing. It is a mental health crisis in the making, because when those babies are pre-teens and older, they will be much more likely to have mental health issues. But that is a story for another day. My focus today is on adolescent users and their brains.


Developing schizophrenia isn’t the only risk to adolescent THC users. Potential lingering results include:


  • Less of an ability to respond to new social situations
  • Greater emotional instability
  • A drop in intellect
  • Less of an ability to focus
  • Worsened impulse control


These are thought to be because of damage to the nerve network in the prefrontal cortex.


Remember the prefrontal cortex? I previously wrote about the prefrontal cortex and the horrific practice, 80 years ago, of destroying it with ice picks (the “lobotomy”)—often for trivial mental health reasons. The prefrontal cortex is where our personality lies. It is the last part of the brain to start developing, and the last to fully develop, finishing up sometime in the mid-20s or even the early 30s.


The prefrontal cortex is the place where rational thought arises. Here is where we make choices to guide our behavior, think carefully through options and hold back impulses. When the prefrontal cortex matures, the child becomes the adult.


I knew none of this back in the 1970s when I was offered marijuana. But I am so, so glad I declined. As far as I know, nothing hindered my still-developing brain from reaching its full potential. And now I am grateful for each and every functional brain cell.

Amy Givler, MD

About Amy Givler, MD

Amy Givler is a family physician in Monroe, Louisiana. She and her husband Don met in 1980 at a CMDA student event her first year of medical school, and they have both been active members of CMDA ever since. Amy graduated from Wellesley College and Georgetown University School of Medicine, and she then completed her family medicine residency at the same indigent-care hospital where she now works part time. She also works at an urgent-care clinic and is the medical director for a Shots for Tots clinic. Amy loves to write and has written many articles and one book, Hope in the Face of Cancer: A Survival Guide for the Journey You Did Not Choose. She and Don have a heart for missions, and hope to do more short-term trips now that their three children have launched from the nest. Connect with Dr. Givler at

1 Comment

  1. Avatar Jerry Wittingen on June 5, 2023 at 7:37 pm

    Thank you for summarizing the deleterious effects of marijuana in adolescents. The widespread legalization for recreational use is proving to be a disaster. Fervent prayer is our best defense against this downward spiral.

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