Addiction 101

Broadly speaking addiction may be defined as impaired control over a reward-seeking behavior from which harm ensues.

It is a genetically influenced disorder (about half the risk is conferred by genetics).


Genetic make-up can affect the degree of reward that individuals experience when initially exposed to a substance or engage in the behavior (e.g., gambling), which in turn, can lead to more and more exposure to the substance. Also, different genes can have different effects that facilitate different pathways into addiction.

People with a certain genetic predisposition (e.g., genes that affect reward sensitivity), for example, may experience much greater pleasure leading to a subsequent desire to increase the frequency and intensity of use; alternatively, they may have genes that affect metabolism which means they experience less reward at the same dose, leading to a desire to increase the amount taken in order to obtain the same level of reward that others might experience at a lower dose.


With a heightened desire to re-experience use of the substance, and potentially exacerbated by other developmental and environmental risk factors (e.g., early adolescent exposure; childhood abuse/neglect; trauma; psychiatric distress; easy accessibility to the substance, low cost) chronic exposure leads to functional changes in the brain as it attempts to adapt to the abnormally high levels of neurochemical release (e.g., dopamine) induced by taking the substance- a process called neuroadaptation.

The brain also changes structurally through both neuronal changes (pruning and cellular death caused by neurotoxicity) & functional neuroadaptations.


These brain changes lead to alterations in cortical (pre-frontal cortex) and sub-cortical (limbic system) regions involving the neuro-circuitry of reward, motivation, memory, impulse control, and judgement.

In heavy chronic users, this can lead to radical and dramatic increases in cravings for the drug as well as impairments in the ability to successfully regulate the impulse to use the drug despite the knowledge and experience of severe consequences.


In order for person to recover from addiction, a person’s brain undergoes a process of re-adaptation to the absence of the substance.

This brain recalibration is perceived by the addicted person as demanding, effortful, uncomfortable, and challenging and takes time as affected individuals often suffer from a decreased ability to experience normal levels of reward for some time after they stop, due to neuroadaptations and down-regulation of receptors that facilitate this experience, (such as dopamine D2 receptors).

The first 3-6 months are particularly difficult and medications, psychosocial treatments, and recovery-supportive living environments can help individuals successfully navigate this difficult period and transition in early recovery. The brain structures and functions may never completely recover to where they once were or would have been in the abstence of the drug exposure, but substantial improvements can be made in light of abstinence and proper nutrition, exercise, and low-stress environmental conditions.



  1. American Society of Addiction Medicine (ASAM): Addiction is a primary, chronic disease of brain reward, motivation, memory and related circuitry. Dysfunction in these circuits leads to characteristic biological, psychological, social and spiritual manifestations. This is reflected in an individual pathologically pursuing reward and/or relief by substance use and other behaviors. Addiction is characterized by inability to consistently abstain, impairment in behavioral control, craving, diminished recognition of significant problems with one’s behaviors and interpersonal relationships, and a dysfunctional emotional response. Like other chronic diseases, addiction often involves cycles of relapse and remission. Without treatment or engagement in recovery activities, addiction is progressive and can result in disability or premature death.
  2. National Institute of Drug Abuse (NIDA): [Drug] addiction is a chronic, relapsing brain disease that is characterized by compulsive drug seeking and use, despite harmful consequences. It is considered a brain disease because drugs change the brain; they change its structure and how it works. These brain changes can be long lasting and can lead to many harmful, often self-destructive, behaviors.


The causes or antecedents of addiction are complex, with interacting biological (i.e., an individual’s genotype or genetic makeup), psychological (i.e., cognitions and beliefs), social (i.e., familial and peer group influences), and some would argue spiritual or existential factors contributing.

The risk conferred by each of these factors differs from individual to individual.


Addiction is classified in widely used diagnostic compendiums such as the World Health Organization’s (WHO) International Statistical Classification of Diseases and Related Health Problems 10 (ICD-10), and the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders 5 (DSM-5).

The diagnostic definitions laid out in these publications capture key cognitive and behavioral aspects of addiction, though by no means include an exhaustive list of the wide array of symptoms associated with addiction.

The ICD-10 and DSM-5 utilize polythetic diagnostic criteria, i.e., they present a constellation of core symptoms of addiction, but do not require a person to meet all these criteria to receive a diagnosis of a substance use disorder (e.g., alcohol use disorder), or behavioral addiction (e.g., gambling disorder). In the list of 11 symptoms in the DSM-5 for instance, people are only required to meet crtieria for two or more symptoms to receive a substance use disorder diagnosis. As such, there may be much individual difference in the way a diagnosable addictive disorder presents in clinical settings.

Diagnostic compendiums such as ICD-10 and DSM-5 are designed to describe and diagnose addictive disorders. They are not, however, designed to describe less severe or problematic substance use (e.g., risky/harmful use) or gambling, which may nevertheless pose significant risk to the individual, and/or be a precursor of an addictive disorder.

The DSM-5 describes substance use disorder:

See Infographic: Diagnosing Substance Use Disorders- Severity Levels

A problematic pattern of substance use leading to clinically significant impairment or distress, as manifested by at least two of the following, occurring within a 12-month period:


  1. The substance is taken in larger amounts or over a longer period of time than intended.
  2. There is a persistent desire or unsuccessful efforts to cut down or control substance use.
  3. A great deal of time in spent in activities necessary to obtain, use, and recover from the substance.
  4. Cravings and urges to use the substance.
  5. Recurrent substance use resulting in a failure to fulfill major role obligations at work, school, or home.
  6. Continued substance use despite having persistent or recurrent social or interpersonal problems caused or exacerbated by the effects of the substance.
  7. Important social, occupational, or recreational activities are given up or reduced because of substance use.
  8. Recurrent substance use in situations in which it is physically hazardous.
  9. Substance use is continued despite knowledge of having persistent or recurrent physical or psychological problems that are likely to have been caused or exacerbated by substance use.
  10. Tolerance, as defined by either of the following:
  11. A need for markedly increased amounts of the substance to achieve intoxication or desired effect.
  12. A markedly diminished effect with continued use of the same amount of the substance.
  13. Withdrawal, as manifested by either of the following:
    • The characteristic withdrawal syndrome for the substance.
    • The substance (or a closely related substance) is taken to relieve or avoid withdrawal symptoms.


A minimum of 2-3 criteria is required for a ‘mild’ substance use disorder diagnosis, while 4-5 is ‘moderate’, and 6-7 is ‘severe’.

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