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Does Marijuana Affect Brain Development?

Mary Jane does not always treat its users fairly; Before jumping to joints, younger users should beware marijuana's strain on the adolescent brain.

By Wendy WeedlerPublished 7 years ago Updated 2 years ago 5 min read

Marijuana can be a very useful substance, but given the relative lack of knowledge about long-term effects, we could all stand to be as educated as possible before engaging. A little cannabis can be great for social gatherings, as it reduces anxiety and temporarily improves mood. However, Mary Jane doesn’t always treat its users fairly. This beautiful plant can turn into a flower of doom amongst younger smokers.

It's pretty well-established at this point that cannabis use will not cause the any physical long term damage, as opposed to alcohol and other substances that can damage the liver and other bodily systems. But there is one question that has yet to be answered conclusively.

Will cannabis have a positive or negative effect on the mind?

We've seen that the effects of marijuana vary by age, specifically by the age at which a person begins using marijuana. While marijuana offers a myriad of cerebral benefits such as creativity and stress reduction, it can impede a developing mind.

Early Adopters

Whereas research on alcohol and adolescents has conclusively proven the danger, marijuana research is less definitive because some of its components have somewhat contrasting effects and long term impact is ill-defined. Specifically, scientists have determined that the cannabinoid CBD has neuroprotective effects, while Tetrahydrocannabinol (THC) the main active ingredient, overwhelms the cannabinoid receptors in the brain so much so that the overall system is dimmed.

THC, then, is the component that should most worry parents when it comes to their teenage kids’ marijuana consumption. Some studies show that regular marijuana use in adolescence (i.e. regular disruption of brain connectivity patterns) is associated with long-term altered brain connectivity and reduced volume of specific brain regions. This risk is even greater now than it was in, say, the 1970s because the concentration of THC has steadily increased (now up to 30 percent—in some strains) while CBD potency has steadily decreased in many strains of marijuana—this, of course, means more harm and less benefit.

Unlike adults, the teenager’s mind is actively developing. Until their mid-twenties, the adolescent brain has not yet fully matured. The most common ill-effects studied in the brains of teenage smokers are:

  • Mental development
  • Brain memory
  • Interactions with others

Smoking marijuana can do a multitude of great things to the body. However, starting at an early age prevents one from experiencing these benefits to their fullest. The increase in THC only makes it harder for young adults to recover after regular usage over a significant period of time.

Memory, Motivation, and Marijuana

The THC in marijuana interferes in the processing of information specifically in the hippocampus, which controls memory formation and emotional and motivational processes. Teenagers do not yet have the full functioning of their hippocampus, which is in part what accounts for stereotypical "teenage irresponsibility" and why marijuana and other substances can be particularly harmful to psychological development at this point in their life.

Through suppressing the neurons located in the hippocampus, THC inhibits accessibility to learned behaviors. It reduces the memory and emotional function in a teen's mind, thereby stunting the ability to respond appropriately to stimuli and keep ones emotions within normal range.

In the short term, THC leads to memory loss and impaired decision making. Teens known for smoking heavily have a wider range of issues. Poor school performance, increased welfare dependence, and higher high school dropout rates are associated with "severe" marijuana usage.

Though the body of research is far from complete, scientists have established that early marijuana use can lead to the following mental health impairments:

  • Increased chances of schizophrenia
  • Increased likelihood of suicidal thoughts
  • Twice the rate of anxiety and depression compared with sober peers

Brain Drain

Indeed, there are several studies that point to evidence of brain changes in young adults who smoke marijuana. In 2013, Dr. Martín-Santos of the University of Barcelona reviewed 43 studies of severe cannabis use in the brain. His study found evidence of altered neural activity and brain abnormalities in marijuana users.

Even though eight of those studies focused on adolescents, the findings were impressive. Functional and structural brain changes appear after adolescents use the drug. After a month of abstaining from marijuana, the changes are still evident.

The study compares regular marijuana users who started before versus after age sixteen. Results suggest that there is a higher risk of long-term brain changes in users who start young; Compared to the comparatively "older" users, early smokers made double the mistakes on cognitive functioning tests that measured abstract thinking, flexibility, and planning. Beyond cognitive effects, younger marijuana adopters were found to smoke more frequently over time, reporting on average that they smoke nearly 25 times a week. By contrast, late smokers were found to smoke on average only half as often (12 times per week).

Now, in comparing effects of usage in general (independent of age), research demonstrates certain key brain changes due to marijuana use. Compared with nonsmokers, smokers demonstrate changes in volume, shape, and gray matter density in two brain regions: the amygdala (involved with decision making and memory) and the nucleus accumbens (involved with reward procession and motivation).

Better Safe Than Sorry

Unlike alcohol, the effects of marijuana usage are subtle. There are over 88,000 alcohol users who die within a year. You will not see this throughout marijuana users. But make no mistake, marijuana is not a risk-free drug.

As suggested earlier, people who smoke pot during their teen years are found to have lower IQs. But in very extreme cases in adults, chronic marijuana usage has shown to lower the IQ by as much as six points. Lowered intelligence is directly correlated with the aforementioned emotional and memory processing dysfunction in the hippocampus.

To be clear, these effects are extreme and do not occur in most cases, but we recommend using marijuana safely—better safe than sorry. Limiting marijuana to just a few times a month is the good benchmark for responsible use.

And if you are under the age of eighteen, relax. You're not going to be living the life of Cheech & Chong. Smoking too early is not going to make your brain rot fast.

Smoke safely and remember to keep your mind right!

marijuana minute

About the Creator

Wendy Weedler

Lives in Washington D.C. Has been part of the legalization movement for decades.

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