Addiction

How drugs and behaviours hijack reward, learning and self-control circuits; tolerance and withdrawal; the brain-disease model and its critics; Rat Park; and effective treatments for opioid, alcohol and nicotine addiction.

What addiction is

Clinically, substance use disorder involves impaired control over use, continued use despite harm, cravings, and often tolerance (needing more for the same effect) and withdrawal (unpleasant symptoms when stopping). Gambling disorder is recognised as a behavioural addiction with similar features.

The brain changes

Addictive drugs act in different ways — opioids on mu-opioid receptors, cocaine by blocking dopamine reuptake, nicotine on nicotinic receptors, alcohol on GABA-A and NMDA receptors — but all increase dopamine in the nucleus accumbens. Researchers such as Nora Volkow (director of the US National Institute on Drug Abuse) describe a cycle of three stages, each linked to brain systems. Binge/intoxication: the basal ganglia and reward circuits, with cues becoming powerfully linked to the drug. Withdrawal/negative affect: the extended amygdala and stress systems, so people use to escape feeling bad. Preoccupation/anticipation: the prefrontal cortex, with weakened self-control and strong cravings. With repeated use, control shifts from goal-directed to more habitual circuits. Kent Berridge and Terry Robinson's incentive-sensitisation theory adds that "wanting" can grow even as "liking" fades.

Disease, choice — or both?

The brain disease model helped reduce stigma and expand medical treatment. Critics argue it underplays choice, environment and the fact that many people recover without treatment. In the late 1970s the Canadian psychologist Bruce Alexander's "Rat Park" experiments reported that rats in an enriched social environment drank less morphine solution than isolated rats; the studies had limitations and mixed replication, but they highlighted the role of environment. Most researchers now favour an integrated view: brain changes are real, and social conditions, trauma, mental health and opportunity shape who develops addiction and who recovers.

Treatment works

Opioid use disorder: medications methadone and buprenorphine substantially reduce deaths and relapse; naltrexone is another option. Naloxone reverses overdoses. Alcohol use disorder: naltrexone, acamprosate and others, alongside therapy and mutual-help groups. Nicotine: varenicline, nicotine replacement and counselling. Evidence-based therapies include CBT, motivational interviewing and contingency management (rewards for abstinence, especially effective for stimulant use). Harm-reduction approaches save lives.