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Addiction and the Brain: 3 Facts You Need to Know

By Michael Howard
Addiction affects the brain in a number of important ways. Learn more about how addiction can alter your brain's processes, and the brain chemistry of addiction treatment.

Although many factors can contribute to the development of substance use disorders, the prevailing theory of addiction places brain chemistry at the forefront. Neuroscience informs modern approaches to understanding and treating drug addiction. A recent study in Physiological Reviews, for instance, defines addiction as a “chronic, relapsing disease of the brain.” With that in mind, here are three key facts about addiction and the brain.

1. Addiction begins in the brain’s reward system. 

The human brain has a reward system that produces feelings of pleasure when stimulated by releasing certain chemicals. We automatically associate these pleasant sensations with the activity by which they were induced. As a result, we tend to remember and repeat that activity.

“The brain is viewed as the primary target organ of addiction,” Andrea Barthwell, MD, Founder of Encounter Medical Group and Member of the Health Advisory Board at RAND Corporation, tells WebMD Connect to Care. “It gets fundamentally changed when one is exposed to a substance. There’s a reward associated with the use of that substance, such as feeling good, or feeling less bad. If there’s a reward associated with the behavior, there’s a tendency to repeat the behavior.”

The National Institute on Drug Abuse reports that in the case of addiction, the rewards are so potent that people are often driven to continue using a drug even if they don’t necessarily think they want to.

“The brain reward occurs in a group of neurostructures in the primitive area of the brain which is responsible for the salience, or the importance, of something in our life,” Barthwell says. “It creates the motivation to do it, the desire for it, and the craving for it. It also creates positive reinforcement for those behaviors.”

2. The brain adapts to substances over time.

Substance abuse causes significant changes to the brain’s circuitry. Known as neuroadaptations, these changes are a major factor in the development of addiction.

“We recognize that once you have had that repeated experience with these chemicals, the desire to repeat using them is set up,” Barthwell explains. “The brain begins to change how it responds to these chemicals, and it reduces the responsiveness in those receptor systems.”

She notes that different drugs interact with different receptors in the body. For instance, opioids bind to your opioid receptor, while THC (the main psychoactive ingredient in cannabis) binds to your cannabinoid receptor.

Although “feel-good” chemicals are responsible for the reward that you experience after first taking these drugs, dependence and addiction are sustained primarily by changes in your brain’s response to them.

“Most people are familiar with the chemical dopamine,” says Barthwell. “It is essential for setting up the initial reward, but not as important for maintaining the dependence when it gets established. In the opioid system, for example, those receptors turn down their responsiveness. You begin to get less of the desired effect, so you have to take more of the chemical. That’s tolerance.”

3. Modern addiction treatments seek to restore brain homeostasis.

A better understanding of how addiction affects the brain has led to new and improved treatment methods. Medication-assisted treatment, for one, combines prescription drugs with therapy and counseling to help patients achieve long-term recovery.

“We’ve developed a system where we can apply a molecule that sits in your receptor system, leaving it in the ‘on’ position so that you don’t experience withdrawal from not taking it,” Barthwell says. “Having a molecule that sits there and gives you a smooth, continuous blood level causes the receptor to stop changing—it has achieved its new balance.”

Examples of medications that help achieve this effect include methadone and buprenorphine. The FDA has approved both for the treatment of opioid addiction.

When these drugs are administered, Barthwell says, “the brain feels that it has achieved its new homeostasis, and you’re not driven to get more of the opioid to cure withdrawal. And because the molecule is sticky and sits there, it’s not causing that receptor to constantly readjust its responsiveness to it. So it stops creating new tolerance.”

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