St. Joseph Mercy Dr. Elizabeth Block Explains Marijuana and the Developing Brain

Dexter Rotary recently welcomed Alyssa Tumolo of SRSLY Dexter and her guest Dr. Elizabeth Block MD, adolescent psychiatrist with St. Joseph Mercy Chelsea, who spoke on the effects marijuana use has on the developing adolescent brain.

Dr. Block began by presenting findings from the Monitoring the Future study conducted by the University of Michigan. It is an annual survey of grades 8, 10, and 12 and looks to find patterns in substance use. The most recent data from 2017 show that 37% of high school seniors had used marijuana in the past year compared to 56% who had used alcohol in the same time-frame.

“Significant findings (of the study) where that the use of vaping is exponentially increasing,” said Dr. Block. “The perceived risk of marijuana usage is declining. This is pertinent because when the perceived risk decreases the actual use increases.”

Dr. Block clarified a few terms for the audience:

  • “Marijuana” is used to describe plants, seeds, and buds from a certain species of plants within the genus Cannabis.
  • “Cannabinoids” are chemicals produced by plants within the genus These are the psychoactive part of the genus Cannabis. Cannabinoids can influence parts of the brain.
  • “Endocannabinoids” are chemicals naturally produced within the body’s nervous system. The brain has receptors to accept and process these natural chemicals.


Alyssa Tumolo (L) of & Dr. Elizabeth Block (R)

“Terms that often come up in discussions about marijuana and cannabis are ‘THC’ and ‘CBD’, explained Dr. Block. “These are two of the components that are found in marijuana. Marijuana actually has over a hundred types of cannabinoids, but these are two of the most well-studied.”

THC is the component has a higher impact on how the brain works. THC is the chemical associated with getting high. It can sharply impact mood which is associated with psychosis. Strains of marijuana today actually have higher concentrations of THC than strains in the past.

“There are some forms of marijuana products that are a very, very concentrated forms of THC”, Dr. Block told Rotarians. “I don’t know if anybody here has ever heard of ‘wax’ or ‘dab’, but that’s THC extracted from the plant usually using something like butane. It can be quite dangerous.”

THC is what’s picked up on a urine drug screen. It’s unique in that it stays in the body for up to several weeks. Showing up on a drug screen doesn’t mean somebody has recently used. This is one of the challenges in telling if somebody is under the influence.

CBD is the other well-known part of cannabis plants that has been getting a lot of attention. It has been attributed for successfully treating certain nervous system disorders. It is widely available from Amazon to Whole Foods. There are many clinical trials currently underway to discover and verify what it is good for.

Synaptic Pruning

“It’s important to know that the brain in an adolescent is not the same as in an adult”, explained Dr. Block. “Our brains are very dynamic. They have the greatest number of cells in them when people are actually two-years-old. People then go through this process of synaptic pruning all the way up to their early twenties.”

Synaptic pruning is the brain process of reducing the number of neurons in the brain to allow for the most efficient and best neural connections. Dr. Block compared it to improving a garden by removing some plants so the others can grow strong. That is what our brains are doing to optimize function by the time we reach early adulthood.

Cannabinoids are actually believed to play a role in the process. There have been imaging studies that have shown that the brains of young users in adolescence actually have some structural changes and functional changes when compared to individuals that have not used.

Dr. Block elaborates, “As I’ve alluded to, there’s an increased risk of use of cannabis on the developing brain. As with anything else it comes down to how much is being used and how often. Some of the changes on the brain that can take place are actually some cognitive alterations including a reduced IQ, reduced attention, and reduced motivation.”

In adults who use, changes in IQ and other measurements of intelligence can normalize if that person abstains from use for a long time. But right now, research shows that adolescence IQ of users also rebounds but not to its original mark.

“Using cannabis has been associated with increased mood problems and even psychosis”, says Dr. Block. “There’s data now that shows exposure to THC is associated with that developing.”

Other Trouble

A popular myth is that cannabis is not addictive, but it is. That is an idea that the scientific community is trying to dispel.

Physical dangers of using marijuana is exposing the lungs to smoke, exposure to dangerous chemicals such as butane used in the extraction process for other pot products, and it can interfere with how other medications are supposed to work.

The greatest impairment from pot occurs 30-40 minutes after use. Cannabis can intensify the effects of alcohol. This is a big problem since most adolescents will use marijuana after they have used alcohol.

In summary:

  • Vaping cannabis is becoming much more common.
  • The perceived risk of use is decreasing.
  • The part of cannabis that is active in the body is called “cannabinoids”.
  • THC is the chemical that has the negative effects and gets people “high”.
  • CBD is believed to have certain health benefits and is also thought to be protective against THC effects.

“Using cannabis can heavily impact brain function”, Dr. Block said in closing. “This has to do with impeding synaptic pruning. Abstaining can help some of these actions normalize but it takes about 3 months. And in an adolescent’s life, a lot is happening. What if those are the months wherein the SATs are taken?”

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