Addiction 101

Addiction: Definitions and key concepts

Key concepts in substance use


When a person needs higher doses of a substance to produce the same effects they experienced during earlier use, they have developed tolerance. People often develop tolerance while they are physically dependent on a substance (Portico, 2017).



When a person reduces or stops their substance use after a period of using regularly, they experience withdrawal symptoms. This results in unpleasant sensations and feelings.

A person’s withdrawal symptoms are opposite to the main effect of the substance used. For example:

    sedative withdrawal creates hyperactivity with dangerous medical complications
    opioid withdrawal includes anxiety, powerful cravings and flu-like symptoms
    stimulant withdrawal consists of depression, insomnia and cravings (Portico, 2017).


Physical dependence

Physical dependence is a bodily state that may develop with regular drug use. It includes withdrawal symptoms and increased tolerance (Portico, 2017).

When at least three of the following occur in the same 12-month period, it is considered physical dependence (WHO, n.d.):

    tolerance to the substance, specifically needing increased doses to achieve the same effects
    physical withdrawal when stopping or reducing substance use
    a strong desire or compulsion to take the substance
    difficulty controlling substance use-related behaviours
    ignoring other interests because of the time needed to get or take the substance, or recover from its effects
    continuing with substance use despite harmful consequences

Addiction 101 © , CAMH.