Drug Dependence, Tolerance & Addiction

Drug Dependence, Tolerance & Addiction

1. Definitions & terminology (the vocabulary problem)

• Drug dependence — an altered physiological state produced by repeated administration of a drug that necessitates the continued presence of the drug to maintain physiological equilibrium; discontinuation produces a characteristic withdrawal (abstinence) syndrome. Historically called "physical dependence"; now simply termed dependence (KDT 8e Ch.6, p.98).
  • Because the essence is adaptation of the nervous system to function normally in the drug's presence, dependence is equivalently called neuroadaptation (KDT 8e Ch.6, p.98).
  • Drugs producing dependence: opioids, barbiturates, alcohol, benzodiazepines (CNS depressants). Stimulants (amphetamines, cocaine) produce minimal/no physical dependence (KDT 8e Ch.6, p.98).
• Drug addiction — a pattern of compulsive drug use characterised by overwhelming involvement with the use of a drug, where procuring and using the drug takes precedence over other activities; the subject feels emotionally distressed without the drug and continues despite known harm. Historically "psychological dependence"; the term addiction is now preferred (KDT 8e Ch.6, p.99).
  • Dependence is a strong impetus for continued use but is not an essential feature of addiction: amphetamines, cocaine, cannabis, LSD produce addiction with little/no physical dependence, whereas drugs like nalorphine produce dependence without drug-seeking (KDT 8e Ch.6, p.99).
• Conceptual/mechanistic separation — "dependence" (formerly physical dependence) and "addiction" (formerly psychological dependence) are distinct: dependence is defined by a withdrawal syndrome and can occur even with non-psychoactive drugs (e.g. sympathomimetic vasoconstrictors, organic nitrate vasodilators, β-blockers); addiction is the compulsive, relapsing pursuit (Katzung 16e Ch.32, p.607).
  • Dependence invariably occurs with chronic exposure, but only a small percentage of users lose control and become addicted; conversely, relapse is common in addicts after successful withdrawal, when — by definition — they are no longer dependent (Katzung 16e Ch.32, p.607).
• Substance use disorder (SUD) — the current DSM-5 umbrella term; diagnosis rests on a pathological pattern of behaviours (not on dependence per se). DSM-5 collapsed the older "abuse" + "dependence" dichotomy into a single SUD on a mild–moderate–severe continuum (G&G 14e Ch.28, p.533; G&G 14e Ch.27, p.519).
  • DSM-5 SUD criteria cluster into: impaired control (larger amounts/longer than intended, unsuccessful efforts to cut down, time spent obtaining/using/recovering, craving), social impairment, risky use, and pharmacological criteria (tolerance, withdrawal) (G&G 14e Ch.28, p.533–4).
  • "SUD" is preferred to "addiction" in healthcare settings as the more neutral term, though SUD is a form of addiction (G&G 14e Ch.28, p.534).
• Reinforcement — the ability of a drug to produce effects the user enjoys, inducing drug-seeking behaviour and the wish to take it again. Opioids and cocaine are strong reinforcers; benzodiazepines are weak reinforcers. The faster a drug acts, the more reinforcing it is — hence inhaled and IV drugs are highly reinforcing (KDT 8e Ch.6, p.99).
• Drug habituation — less intensive involvement; withdrawal produces only mild discomfort, dependence absent (tea, coffee, tobacco, social drinking). The difference between addiction and habituation is only quantitative; KDT recommends avoiding "habituation" as a distinct term (KDT 8e Ch.6, p.99).
• Drug abuse — self-administration of a drug in a manner/amount deviating from approved medical and social patterns in a given culture/time; conveys social disapproval. For regulatory agencies, abuse = any use of an illicit drug (KDT 8e Ch.6, p.99).
  • Two major patterns: (a) continuous use — drug taken regularly to remain under its influence (opioids, alcohol, sedatives); (b) occasional use — taken off-and-on for pleasure/recreation/sexual enhancement (cocaine, amphetamines, psychedelics, binge drinking, cannabis, solvents) (KDT 8e Ch.6, p.99).
• Substance-induced disorders — distinct from SUDs; a substance-specific syndrome from recent ingestion (intoxication). Intoxication is reversible and common; substance-induced mental disorders can be severe and occasionally leave persistent CNS syndromes (e.g. alcohol → depressive symptoms in intoxication, anxiety in withdrawal; stimulants/synthetic cannabinoids → psychotic/anxiety disorders) (G&G 14e Ch.28, p.536).
• ⚠ Terminology drift — DSM-5 (G&G, Stahl) frames everything as SUD; KDT retains the classical dependence / addiction / habituation / abuse lexicon. They describe the same phenomena; the exam answer should give both the DSM-5 continuum and the classical KDT definitions.