What is Addiction?

A disease involving changes to the architecture of the brain.


Addiction is a complex disease involving changes to the brain. These changes include altered functioning of the reward-and-motivation system and the Air Traffic Control system.

Addiction is marked by a three-stage cycle of behaviour involving the following: 

  1. Bingeing and intoxication: Excessive use of a substance or behaviour.
  2. Withdrawal or negative affect: A negative emotional state in the absence of the substance (including dysphoria, emotional pain, malaise, irritability, and sleep disturbances).
  3. Preoccupation and anticipation: The compulsion to seek out substances and behaviours again, leading an individual back to the bingeing and intoxication stage. 

Addiction is a chronic disorder with the potential for recurrence. With good-quality treatment, an addicted person can recover.

While our understanding of substance misuse and addiction continues to develop, there is emerging evidence that the compulsion to engage in certain behaviours involves similar changes to brain systems as the compulsion to misuse substances like drugs or alcohol. Addictions can be grouped as follows:

Substance-related Addictions

This includes compulsive misuse of any of the following:

  • Tobacco
  • Alcohol
  • Street drugs
  • Prescription drugs 

Behavioural, Or Process, Addictions

Although less well studied, many behaviours appear to have reinforcing properties and may involve excesses related to:

  • Gambling
  • Food
  • Sex
  • The Internet
  • Video games
  • Work 

What Increases Risk Of Addiction?

No one is destined from birth to become an addict later in life. Certain genetic factors increase the likelihood of addiction, but so do experiences that affect how the brain develops. Experiences that occur early in childhood, even as far back as the prenatal and postnatal periods, can alter brain architecture in ways that make a person more or less likely to develop an addiction later in life. For example, the quality of the infant-caregiver interaction and exposure to Toxic Stress both have direct effects on the brain systems responsible for regulating emotions and stress. In other words, children who are exposed to toxic stress may grow up to be adults who have difficulty coping with stress, anxiety, and mood. This can lead individuals to attempt self-medication in an effort to alleviate these effects. 

The Science Of Addiction

Becoming addicted is gradual process involving the interplay of genetic factors, early experiences, and the effects of potentially addictive substances and experiences on specific brain systems over time. 

Reward and Motivation

Compounds and experiences with addictive potential activate the brain’s reward circuitry. These triggers are also called reinforcers because the pleasurable feeling we get from them makes us more likely to engage in them again. Both alcohol and illicit drugs are powerful reinforcers, as are food, sex, and gambling. These substances and experiences cause the release of large amounts of the neurotransmitter dopamine in the brain’s reward system. Heightened levels of dopamine over long periods of time produce structural and chemical adaptations in these circuits as the brain tries to regain a state of balance. These adaptations ultimately underlie behaviours like bingeing, escalating use, and symptoms of withdrawal when the drugs or experiences are taken away.

Air Traffic Control

Another brain system changed by addictive behaviours is the air traffic control system (also called the “executive function” system) in the pre-frontal cortex of the brain. The ability to resist strong urges or to follow through on decisions to stop an addictive behaviour may be impaired in the addicted brain. Thus, although a person may be sincere about intending to stop a behaviour, he or she may find that a weakened air traffic control system saying “stop” is overpowered by an altered reward-and-motivation system that causes powerful cravings for the addictive substance or activity. Appropriate treatment can help improve functioning of the air traffic control circuits, thus helping a person regain control. 

ADHD Increases Risk

Research has now shown that children with poor impulse control, such as those with attention deficit hyperactivity disorder (ADHD), may also be at risk for addiction. These children may engage in risky behaviours at earlier ages and more frequently than other children. From a prevention perspective, understanding the factors that contribute to developing an addiction is crucial so that we can monitor and mitigate risk appropriately. Read more about childhood ADHD and future addiction (third-party research).


Research shows that substance and behavioural addictions can occur within the same individual and that multiple variants of substance or process addiction can be expressed at the same time. Thus, people can have multiple addictions, with each addiction being active to differing degrees of severity. Additionally, depression and anxiety frequently accompany addiction as co-morbid factors.



The U.S. Department of Health and Human Services has a detailed chapter about the neurobiology of addiction in their report Facing Addiction in America: The Surgeon General's Report on Alcohol, Drugs, and Health. Download Chapter 2: "The Neurobiology of Substance Use, Misuse, and Addiction" for more information. Download the complete report here.  

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