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Addiction & the Brain: How Drugs Affect the Brain

May 4, 2022

Table of Contents

Long-term drug use changes the size, shape, and function of brain cells

Depending on the type and amount of drug used, these changes can be reversible but can sometimes be irreversible .[1] The changes can have an impact on perception and thought processes, mood management, impulsivity, and behavior. 

It takes time to undo the damage, but sustained recovery can help to minimize changes to the brain long term. 

Here’s what you need to know about the brain and addiction. 

The Disease of Addiction 

There are a few different ways of looking at addiction in the professional medical and mental health fields, but the one that is most commonly accepted and upheld by the American Medical Association and the American Society of Addiction Medicine is called The Disease Model.[2] We understand that addiction, like other chronic diseases, is usually caused by a combination of genetic risk and underlying behavioral and/or psychological disorders. 

Addiction disorders are thought to be highly heritable. Some studies estimate genetic risk accounts for about 50% of someone’s risk of developing an addiction disorder [3] This means that a person who has a parent, sibling, or other biologically-related relative with addiction has an increased risk of developing an addiction disorder. 

This does not mean that everyone who has addiction in their family will develop a substance use disorder (SUD), but it is currently thought to increase their risk. also doesn’t mean that those with no family addiction issues will escape SUD if they begin to drink or use drugs - individuals with no family history of SUD can still develop SUD themselves. 

There are a number of factors that contribute to the development of substance use disorders. For families with a loved one living with addiction, know that your loved one: 

  • Will not be able to simply decide to stop being addicted to any substance just like they can’t decide to stop having diabetes or high blood pressure.
  • Will likely require medical and psychological intervention that potentially includes medication.[4]
  • May relapse and use drugs and alcohol again during the course of treatment, though this is less likely if they are enrolled in Medication for Addiction Treatment (MAT). 
  • Will need time to transition into a new lifestyle that doesn’t include drug use. 

How Do Drugs Work in the Brain?

Depending on the method of ingestion — such as oral ingestion, smoking, or intravenous drug use — drugs begin to alter the function of the brain somewhere between minutes to hours of ingestionWith oral ingestion, it takes up to 20 minutes or more to feel the effects because the substance is processed through the intestines. Intravenous drug use prompts almost instant changes in the body in a matter of seconds to minutes.

Once in the bloodstream, the substance will bind to receptors that then alter neurotransmitters in the brain. This effects how the brain processes, sends, and receives information — both how external stimuli are perceived and how internal information is processed.[5]

Some substances actually work in a similar way to natural neurotransmitters, but they don’t send the same messages. Other substances just block neurotransmitters and stop them from functioning. 

In some cases, drug use can cause some neurons to die, either with too much of a substance at one time or over time with continued exposure to substances.[6]

What Parts of the Brain Are Affected by Drug Use?

Drug use will impact different parts of the brain to different degrees depending on the substance being used, and the amount and duration of use. 

In general, however, these are the parts of the brain thought to be most impacted by drug use:[7]

  • Basal ganglia: Sometimes called the “pleasure pathway” in the brain, the basal ganglia plays a role in developing positive motivation When this region of the brain is repeatedly stimulated by drug use, it can increase the urge to take the substance repeatedly and decrease the person’s ability to avoid compulsive use.
  • Extended amygdala: This part of the brain plays a big part in the feelings of anxiety and agitation that come with trying to stop a habit that usually triggers the pleasure pathway. The longer that this part of the brain is exposed to substance use, the more it wakes up when that substance is removed, creating psychological cravings and other symptoms of withdrawal. 
  • Prefrontal cortex: This is the decision-making part of the brain and one of the last parts of the brain to fully develop in humans. It may stop developing when exposed to drug use, which can mean that the developing ability to problem solve and manage impulsive behavior is stalled for a period of time or forever. 
  • Brain stem: This part of the brain controls autonomic function — the body functions that we don’t have to think about like breathing and heart rate. Some drugs can overtake this part of the brain and shut it down, triggering what we call overdose and potentially death. 

How Addiction Develops in the Brain

Initial or first-time use of a substance will trigger the pleasure pathway in the brain (the basal ganglia), causing the person to experience a euphoric high. 

When the high fades, the amygdala kicks in, creating cravings and/or feelings of agitation or restlessness that will be appeased by taking more of the drug [7] This creates a reward pathway where the individual’s brain is actually sending cravings/signals to take more of the drug. 

Long Term Effects of Drug Use in The Brain

It is very hard to study the long term effects of drug use on the brain. Outcomes vary greatly between individuals depending on their personal brain chemistry, genetics, what substances they used, and for how long. There are certain drugs that are known to cause long term, irreversible damage. For example, patients with alcohol use disorder (AUD) can develop a condition called wernicke’s encephalopathy which can then progress to a condition called Korsikoff’s syndrome which involves long term memory loss, learning disabilities, and decreased cognition that is irreversible. 

The long term effects of opioid and heroin use are less clear, although it is thought that Repeated exposure to opioids can trigger the changes that occur in the brain to continue long after they stop using, including memory loss and decreased cognition.[8]

Addiction & the Brain FAQ

How does addiction affect the brain? 

Use of substances disrupts neurotransmitters and triggers the pleasure pathway, or reward path, in the brain. When this pathway is repeatedly stimulated, it becomes harder and harder to manage compulsive behavior.[5] In some cases, neurons may die as well which can potentially lead to lasting, irreversible damage.[6]

What part of the brain is responsible for addiction? 

There are multiple parts of the brain that play a role in the development of addiction, including the basal ganglia, amygdala, and prefrontal cortex.[7] 

Are the brains of people with substance use disorder different?

No two people’s brains are exactly alike, but people who have substance use disorder will find that their brains will function differently during and after addiction as compared to before addiction. 

Each person’s experience in addiction and recovery will vary, but it is normal to take a few months to a few years to create a  life that does not involve active drug or  alcohol use. 

Can the brain recover from addiction?

Yes, most of the time, the brain can recover from the damage of active addiction. Just like any healing process, it can take months or years for the brain to downregulate the receptors that have been altered by repeated drug use. While a lot of these chemical changes are reversible, some degree of damage may be irreversible, depending on the substances used and the duration of use. 

Be patient with yourself and with your brain - your brain needs time to re-adapt after discontinuing substance use. Reach out to your doctors, and loved ones for support as your brain continues to re-adjust after long term substance use. 

Elena Hill, MD, MPH

Elena Hill, MD; MPH received her MD and Masters of Public Health degrees at Tufts Medical School and completed her family medicine residency at Boston Medical Center. She is currently an attending physician at Bronxcare Health Systems in the Bronx, NY where she works as a primary care physician as well as part time in pain management and integrated health. Her clinical interests include underserved health care, chronic pain and integrated/alternative health.

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  1. The Neurobiology of Substance Use, Misuse, and Addiction. U.S. Department of Health and Human Services. 2016. Accessed March 2022. 
  2. Is Addiction a Disease? Partnership to End Addiction. March 2022. Accessed March 2022. 
  3. Genetics: The Blueprint of Health and Disease. National Institute on Drug Abuse. August 2019. Accessed March 2022. 
  4. Treatment Approaches for Drug Addiction. National Institute on Drug Abuse (NIDA). January 2019. Accessed March 2022. 
  5. Understanding the Effects of Drugs on the Brain: A Look at the Damage and Potential for Treatment. WGN Morning News. January 2022. Accessed March 2022. 
  6. Brain and Addiction. National Institute on Drug Abuse. June 2019. Accessed to March 2022. 
  7. Drugs, Brains, and Behavior: The Science of Addiction. National Institute on Drug Abuse. July 2020. Accessed March 2022. 
  8. Facing Addiction in America: The Surgeon General's Report on Alcohol, Drugs, and Health: Chapter 2 – The Neurobiology of Substance Use, Misuse, and Addiction. National Center for Biotechnology Information. 2016. Accessed March 2022.

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