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Knowledge Exchange > Primary Care > Toolkits > Addiction Toolkit > Fundamentals of addiction > Addiction FAQ: What are physical dependence, tolerance and withdrawal?

Fundamentals of addiction
What are physical dependence, tolerance and withdrawal?

© 2010 CAMH and St. Joseph’s Health Centre, Toronto

Physical dependence

Physical dependence is an adaptive physiological state that occurs with regular drug use and results in a withdrawal syndrome when drug use is stopped. It is usually associated with increased tolerance. Physical dependence alone does not imply addiction.


  • Tolerance is a condition in which higher doses of a drug are required to produce the same effect experienced during initial use.
  • Tolerance is often associated with physical dependence.
  • In therapeutic use of a drug with psychoactive effects (e.g., morphine for chronic pain relief), patients tend to become tolerant to the psychoactive effects (e.g., euphoria, reduced anxiety or sleep inducement), but not the therapeutic effects. A patient seeking higher doses of, for example, a narcotic may be seeking the psychoactive effects of the drug (e.g., euphoria, relaxation, increased concentration) to which he or she has developed tolerance.


  • With regular use of a substance, biochemical and structural adaptations take place in the brain.
  • Withdrawal is the constellation of symptoms and signs that a person experiences when, after a period of regular use, the quantity of available substance in the brain is reduced.
  • Upon abstinence, central nervous system receptors take days or weeks to normalize.
  • Symptoms and signs of withdrawal are opposite to the main effect of the drug. For example:
    • Sedative withdrawal creates autonomic hyperactivity with dangerous medical complications.
    • Opioid withdrawal is accompanied by anxiety, powerful cravings and flu-like symptoms.
    • Stimulant withdrawal consists of depression, insomnia and cravings. 

Contents of Fundamentals of Addiction


FAQ: What is addiction?

FAQ: Mental health and addiction

FAQ: Asking about substance use

FAQ: Reporting to the Ontario Ministry of Transportation

FAQ: Methods of managing addiction

Tools and resources

Patient handouts



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