The Science of Addiction

Addiction is a treatable medical illness.

First things first: Addiction is not a moral failing, a choice, or a character flaw. Addiction, also referred to as substance use disorder, is an illness. All major health experts agree: The American Medical Association, The National Institutes of Health, the World Health Organization, and more.

Treatment for addiction is highly effective. Decades of scientific research show what treatments work best—but one size does not fit all. From personalized plans to therapy and medications, learn what to look for in addiction treatment.

How does addiction affect the body?

It has a lot to do with brain chemistry.

The human brain is wired to reward us when we do something pleasurable. Exercising, eating, and other behaviors that are directly linked to our survival trigger the release of a neurotransmitter called dopamine.

This not only makes us feel good, but it encourages us to keep doing what we’re doing. It teaches our brains to repeat the behavior.

Drugs trigger that same part of the brain: the reward system. When someone uses a substance—be it marijuana, opioids, cocaine, or other drugs—their brain releases lots of dopamine. This process tells the brain that this is a behavior that should be remembered and repeated.

Not everyone who uses substances becomes addicted by this process, but if you’re already at risk, this is where the cycle of addiction can begin. That’s because, according to the National Institutes on Drug Abuse (NIDA), “large surges of dopamine ‘teach’ the brain to seek drugs at the expense of other, healthier goals and activities.”

Once someone is addicted, they’re not using drugs to feel good — they’re using drugs to feel normal.

Studies have shown that consistent drug use severely limits a person’s capacity to feel pleasure at all. That’s because, over time, drug use leads to much smaller releases of dopamine. The brain’s reward center is less receptive to pleasure and enjoyment, both from drugs as well as from everyday sources, like relationships or activities that a person once enjoyed. Once the brain has been altered by drug use, it requires more and more of a substance just to function at a baseline level.

An addicted brain causes behavior changes.

Brain imaging studies from people with substance use disorders show changes in areas of the brain that are critical to judgment, decision making, learning and memory, and behavior control. Scientists believe that these changes alter the way the brain works and may help explain the compulsive and destructive behaviors of addiction.

A promising student might see his grades slip. A bubbly social butterfly might suddenly have trouble getting out of bed. A trustworthy sibling might start stealing or lying. Behavioral changes like these are directly linked to a changing brain.

Addiction also creates cravings. These cravings can be painful, constant, and distracting. What’s more, withdrawal from substances is a painful, whole-body experience. Once someone is addicted, responding to cravings and avoiding withdrawal become their most important needs.

Addiction can happen to anyone. 

It’s not about your background, where you grew up, or how much money you make. Addiction can happen to anyone. Still, researchers have identified what kinds of experiences and biological circumstances put some people at greater risk than others.

Why do some people get addicted but others don’t?

Substance use alone doesn’t cause addiction. Addiction is a complex illness that arises in a person based on their unique circumstances. These are the most commonly identified risk factors for addiction:

Biology: Scientific research has shown that 40–60% of the likelihood that a person will develop addiction comes from genetics. This includes both a family history of the illness as well as epigenetics, which are "the effects environmental factors have on a person's gene expression." Plus, if you have a behavioral health disorder like depression or anxiety, your risk of addiction also increases. 

Environment: Exposure to traumatic experiences has been shown to increase a person's risk of developing a substance use disorder. These experiences could happen at school, at home, or out in the community. 

Using drugs for the first time at a young age can also increase addiction risk. Also, snorting or injecting drugs can increase the risk of becoming addicted to those drugs, due to the extreme way the drug is delivered into the body (and the quickness with which the feeling fades).

So, why do some people become addicted when others don’t? Ultimately, the answer lies in a person’s unique brain chemistry and lived experiences. Most people who develop addiction are looking to heal or soothe themselves in some way. It’s crucial to understand why that is, and work to address it, as part of a person’s treatment plan and journey to recovery. 

Harsh consequences, shame, and punishment are simply not effective ways to heal a person’s addiction.

A person can’t undo the effects drugs have had on their body chemistry through sheer willpower. Like other chronic illnesses, such as asthma or type 2 diabetes, ongoing management of addiction is required for long-term recovery. And there are plenty of evidence-based solutions that can help people with substance use disorders get there.

Today, more doctors, policymakers, and everyday Americans are embracing the science of addiction.

That’s good news. But it’s important to remember that addiction has always been an illness—even when our health care systems were most hostile to the idea, and even when the people American culture primarily associated with drugs and addiction were Black or Latinx Americans. Learn about the social impact of addiction in America.