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The Science of Prevention

Brain research has given us a better understanding of addiction than ever before, and the technology that has developed in the past 50 years has given us an even closer glimpse into the brain structures and functions that contribute to and are impacted by substance use. Although we still have much to learn, we have come to understand some fundamental aspects of addiction that guide modern prevention efforts.


Certain systems in the brain are particularly impacted by substance use.

Although substance use affects all parts of the brain in some way, there are certain parts of the brain that are particularly vulnerable and that become hijacked when a substance use disorder occurs. The first is the limbic system, which is comprised of several structures, such as the basal ganglia and the amygdala. The structure of this system are in charge of our emotional responses, our memory, and our survival instincts. The limbic system is located in the center of our brain, and each time we complete a task that meets our survival needs–such as eating, drinking, having sex, or caring for our young–our brain is flooded with a neurotransmitter known as dopamine, which is a chemical that helps brain cells communicate with each other and reinforces the sensations of reward and pleasure that we experience with an activity. The limbic system then stores that information so that we will remember in the future that we experience pleasurable, rewarding sensations when we perform a certain action. Substance use interferes with the way that neurotransmitters are produced. Some drugs mimic naturally occurring neurotransmitters, confusing the brain and causing it to produce less of a neurotransmitter on its own. Other drugs cause the brain to overproduce natural neurotransmitters, also disrupting the communication between cells.

The second part of the brain that is overridden by addiction is the prefrontal cortex. Located at the very front of the brain, this is the part of the brain that is responsible for higher decision-making, such as weighing the consequences of an action. It is often described as the part of the brain that ‘pumps the brakes’ on the limbic system so that we do not act on instinct alone. It is also the part of the brain that separates us most from other animals.

When substance use starts to become problematic, it is because the limbic system begins to associate the substance use behavior with survival. The brain thinks that it needs the substance in order to survive, and the prefrontal cortex has a difficult time overriding that message in the limbic system. That is why people who experience addiction often do things that negatively impact themselves and others. Although someone who does not have a substance use disorder might question how a person could do things that are destructive and even hurtful, the ability to anticipate the consequences of their actions has been undermined by the substance use.

What happens to your brain during adolescence can have long-lasting impacts.

By the time we are in elementary school, our brains are about as big as they will ever be. So during adolescence, our brain development is not really about growing the size of our brain; it is focused on developing the structures and functionality of our brain. This is done through a process of pruning and myelination. As children, we have millions more brain cells–called neurons–than we will ever need in our lives. These neurons are connected to each other by axons. As we develop our skills and interests in certain areas during adolescence–such as making music or playing a sport–our brains naturally begin to prune or cut away the neurons that we are not using so that we can focus all of our energy on the neurons that we use regularly. Meanwhile, in order to improve the connections between those remaining neurons so that they can communicate with each other with speed and efficiency, our brains begin to insulate the axons that connect the neurons with a fatty substance known as myelin. Much like the protective covering of an electrical wire improves the ability of a wire to quickly deliver electricity in a circuit, this process of myelination allows our brains to process information rapidly. It is important to note that this developmental process lasts throughout adolescence and is not completed until a person is 25-26 years old, and it also occurs sequentially, starting in the back of the brain and moving towards the front, so that the last part of the brain to fully develop is the prefrontal cortex, the part of the brain that is in charge of high level decision making and anticipating consequences of our actions.

There is strong evidence that most cases of addiction in adulthood might be related to the substance use that a person’s brain was exposed to during adolescence. Many medical professionals and researchers now view addiction as a ‘pediatric disease’ because for every 10 adults who live with a substance use disorder, 9 of them started using substances before age 18. Of course, that does not mean that 90% of young people who try a substance will go on to become addicted; each individual person’s risk and protective factors ultimately influence whether or not someone will become addicted. But adolescent substance use is a significant risk factor that is further compounded by the age of the person when they first started using a substance, the strength or toxicity level of the substance, and the frequency with which the substance was used. And although many current adults used substances as teens and never experienced a substance use disorder, it is important that they do not generalize their life experience to their own teens. The reality is that many of today’s teens experience adolescence very differently than their parents did at the same age. Academic and extracurricular success, college aspirations, and the magnifying glass that social media and technology bring to social interactions can make being a teen today a very stressful experience. Additionally, the substances that are easily accessible today tend to be much stronger than many of the substances teens used 20-30 years ago. Candy-flavored hard liquors, concentrated nicotine cartridges for vaping devices, and prescription pills are easily accessible to most U.S. teens. The potency of marijuana has also increased significantly. In the 80s and 90s, marijuana was about 4% THC (tetrahydrocannabinol, the psychoactive component of marijuana). Today, the average amount of THC in marijuana products is closer to 20% and even as high as 30%.

Ultimately, our message to young people is delay, delay delay! Use of any addictive substance while the brain is still developing increases the chances of future use of that and other addictive substances. Waiting until at least 21 to try alcohol, nicotine, marijuana, or other substances significantly decreases the chance that a person will ever experience addiction.