Describing Addiction

Defining Addiction

Addiction is a complex, chronic condition characterised by compulsive engagement with a substance or behaviour despite harmful consequences and loss of control. Understanding addiction requires distinguishing several related but distinct concepts: physical dependence, psychological dependence, tolerance, and withdrawal. Griffiths (2005) proposed a widely used components model, identifying six core features common to all addictions: salience (the activity dominates thoughts and behaviour), mood modification (the activity changes emotional state), tolerance (increasing amounts needed for the same effect), withdrawal symptoms (on cessation), conflict (with other activities and relationships), and relapse (return to the activity after abstinence).

Physical and Psychological Dependence

Physical dependence occurs when the body adapts physiologically to the presence of a substance, requiring it for normal functioning. Removal of the substance produces physical withdrawal symptoms — the body's attempt to restore homeostasis. Physical dependence is particularly pronounced with alcohol, opioids, and benzodiazepines.

Psychological dependence refers to an emotional and motivational need for the substance or behaviour. It is characterised by intense craving, preoccupation, compulsive engagement, and continued use despite awareness of harm. Psychological dependence is arguably more persistent and harder to treat than physical dependence: even after physical withdrawal is complete, psychological craving may continue for months or years and is the primary driver of relapse.

Tolerance

Tolerance refers to the process by which the body's response to a substance diminishes with repeated exposure, so that increasing doses are required to achieve the same effect. Two mechanisms underlie tolerance:

• Pharmacodynamic (neural) tolerance: neurotransmitter receptors become less sensitive or are reduced in number (downregulation) in response to chronic stimulation by the drug
• Metabolic tolerance: the liver produces more enzymes to break down the drug more efficiently, reducing blood plasma concentration

Tolerance has important clinical implications: as the user escalates doses, the gap between the therapeutic or recreational dose and the lethal dose narrows — greatly increasing the risk of accidental overdose, particularly in opioid users whose tolerance drops rapidly after a period of abstinence.

Withdrawal Syndrome

Withdrawal syndrome is the characteristic cluster of symptoms that appears when a physically dependent individual reduces or stops their substance use. The specific symptoms reflect the pharmacological action of the substance and are broadly opposite in nature (rebound effects):

• Alcohol: tremors, sweating, nausea, anxiety, hallucinations, and — in severe cases — seizures and delirium tremens (DTs)
• Opioids (heroin, morphine): nausea, vomiting, diarrhoea, muscle cramps, insomnia, anxiety, and intense craving
• Nicotine: irritability, anxiety, difficulty concentrating, restlessness, and increased appetite

Withdrawal severity is determined by the substance, the duration of use, the degree of physical dependence, and individual differences. Alcohol and benzodiazepine withdrawal can be medically life-threatening; opioid withdrawal, though extremely distressing, is rarely fatal in otherwise healthy adults.