The Ghost in the Addict. By Shepard Siegel. The MIT Press. £33 (pb). 192 pp. ISBN 9780262547970.

The brain disease model of addiction has been elaborated in detail over the past three decades by neuroscientists funded by the US National Institute of Drug Abuse. Although the model has produced many valuable insights that have challenged stigmatising views of the problem and stimulated treatment research, it is just one of more than a dozen competing theories that have utility.¹ Shepard Siegal, a professor of psychology at McMaster University in Canada, has produced an engaging and in-depth account of one of these ‘other’ theories, drawing on a half-century of research into Pavlovian conditioning. He begins by describing the anticipatory homeostatic correction that occurs in the brain in response to use of psychoactive substances, and how this protects the user from overdose. Taking a regular dose of opioids through the usual route may cause an individual to overdose simply because the drugs are administered in a novel environment. Siegal unravels this mystery by carefully elaborating on the influence of classical conditioning on the development of addiction. The drug-preparatory response is gradually paired with various external (places, people, times) and internal (thoughts, feelings, emotions) cues, until the cue alone elicits a conditioned response. As this response counteracts the effect of the substance it is often mislabelled as a ‘withdrawal response.’ However, the withdrawal response is not due to the effects of previous drug administration, but rather represents the body's preparation for the next drug administration. This preparatory response can ‘haunt’ people like a ghost long after they have stopped regular use.

This is a relatively short book that does not utilise statistical data or neuroimaging scans, but instead draws on a range of literary and scientific sources, re-interpreting the findings of some of the classic studies in the field along the way. Siegal explains why Temperance legislation failed to control the problem, and why the best possible treatment in the Lexington ‘narcotic farm’ inevitably ended in relapse when the individual returned to their home environment. Conversely, the geographic cure often works, illustrated by the famous evaluation of opioid use by soldiers returning to the USA from the Vietnam War. The narrative covers opioids, alcohol and cigarettes, and explains why both small doses of the substance and stress can function as conditional stimuli for eliciting craving. These ideas are applied to the challenge of treating addiction, and the limitations of cue-exposure therapy are explored. The author ends by placing these ideas in the context of the disease model of addiction, concluding that ‘the brains of drug users are different as a result of their conditioning history—not damaged, just different.’