Drug Dependence

  • Drug dependence is a syndrome comprised of physical dependence and psychological dependence
  • Its usage has replaced the older, ambiguous term "drug addiction"

Physical Dependence

  • A complex process whereby chronic administration of a drug results in resetting of the body's homeostatic mechanisms and a new equilibrium point is reached
  • It is characterised by tolerance and withdrawal  syndrome on cessation of administration of the drug, which disturbs the new equilibrium point
  • Tolerance and withdrawal are physiological reactions and do not imply psychological dependence

Psychological Dependence

  • The state where drug taking becomes a need which surpasses all other aspects of life


  • The phenomenon whereby increased amounts of drug are needed to be taken to achieve the same drug effect

Withdrawal Syndrome

  • A constellation of signs and symptoms that occurs after the abrupt cessation of a chronically administered drug


  • A chronic state of physical or psychic dependence on the effects of a drug beyond that required to achieve a recognised therapeutic outcome
  • This term has been replaced by the term "drug dependence"

Opioids & Dependence

Opioid Tolerance

  • Tolerance begins 12-24 hrs after administration and peaks in 2 days
  • May be due to
    • down regulation of receptors
    • uncoupling from secondary messengers
    • ↓ affinity for opioid receptors

Opioid Withdrawal Syndrome

  • Withdrawal occurs 15-20 hrs after cessation and lasts 5-7 days
  • Symptoms include
    • yawning
    • coryzal symptoms
    • abdominal pain
    • diarrhoea
    • anxiety
    • tremor
  • Can be treated with benzodiazepines or clonidine