Addiction is classified as a chronic, treatable medical disease of the brain by the American Society of Addiction Medicine (ASAM), whose 2019 definition ties it to interactions among brain circuits, genetics, the environment and a person’s life experiences. Two decades of research, reviewed in 2016 by the directors of the U.S. National Institute on Drug Abuse and the National Institute on Alcohol Abuse and Alcoholism, back that classification. The brain changes behind addiction reach the reward and self-control circuits and outlast withdrawal, so addiction rehab that stops at detox leaves that repair unfinished.
What Does It Mean to Call Addiction a Brain Disease?
The DSM-5 grades substance use disorder as mild, moderate or severe, with the 2016 review treating addiction as equivalent to the severe grade, where a person keeps using compulsively even after deciding to stop. ASAM holds that prevention and treatment for addiction succeed about as well as they do for other chronic diseases.
That comparison with long-term illness goes back to a 2000 review in the Journal of the American Medical Association. McLellan’s team compared alcohol or drug dependence with type 2 diabetes, hypertension and asthma. Dependence, they found, leaves lasting changes in brain chemistry as well as brain function. Medication adherence and relapse rates proved similar across all four conditions, with 40% to 60% of patients treated for alcohol or other drug dependence returning to active use. To the authors, the results favoured long-term care built on medication management and continued monitoring, the way other chronic illnesses are treated.
What Happens Inside an Addicted Brain?
Every known addictive drug triggers a sharp release of dopamine in the brain’s reward regions. With repetition, dopamine cells start firing in response to cues that predict the drug, such as a room, a person or a mood. Writing in the New England Journal of Medicine, Nora Volkow, George Koob and Thomas McLellan describe addiction as a repeating three-stage cycle.
| Stage | Brain regions involved | What the person experiences |
| Binge and intoxication | Reward regions of the striatum, including the nucleus accumbens | Euphoria; cues start to set off craving |
| Withdrawal and negative affect | Extended amygdala | Low mood, anxiety, restlessness, stronger stress reactions |
| Preoccupation and anticipation | Prefrontal cortex, including the orbitofrontal and anterior cingulate cortex | Obsessing over the drug, planning to get it, relapse |
Pleasure fades as the cycle repeats, because in people with addiction a dose releases far less dopamine than it does in someone who has never used. Relationships and hobbies lose their appeal along with the high. Next, CRF and the opioid peptide dynorphin drive an overactive “antireward” system that leaves them using for brief relief from distress more than for pleasure.
In the prefrontal cortex, which governs self-control, weakened dopamine and glutamate signalling erode the ability to resist urges or follow through on a decision to quit. Volkow’s work traces part of that loss to dopamine D2 receptors, whose expression drops in addiction to cocaine, methamphetamine, alcohol, heroin or nicotine, with marijuana as the exception.
Why Does Addiction Take Hold in Some People and Not Others?
Only about 10% of people exposed to addictive drugs go on to show the most severe features of addiction, according to the 2016 review. Genes account for an estimated 40% to 60% of the variation in risk, a figure Volkow published in 2005 that includes the way inherited traits interact with a person’s surroundings.
Several other influences raise vulnerability, starting with a family history of addiction or drug use that begins in adolescence. The NEJM authors also name socially stressful environments with weak family support or easy access to drugs, along with mental illnesses such as mood disorders, ADHD, psychoses or anxiety disorders. Age carries extra weight because the prefrontal networks that govern judgment do not fully mature until 21 to 25 years of age.
Canadian survey data reflect that youth risk, since Statistics Canada’s 2022 Mental Health and Access to Care Survey found that 3.8% of Canadians aged 15 and older met diagnostic criteria for a substance use disorder in the previous 12 months, compared with 8.5% of those aged 15 to 24.
Where Do Critics of the Brain Disease Model Push Back?
Objections summarized in the 2016 review held that a disease label excuses irresponsible or criminal behaviour. Other critics noted that no genetic or brain abnormality appears consistently in everyone with addiction, with many pointing to people who recover without any treatment.
A newer wave of criticism prompted a 2021 paper in Neuropsychopharmacology by Markus Heilig and five co-authors. The critics it answered had called the model deterministic, said it overstates compulsion, faulted it for ignoring how differently people reach remission and noted that no specific neural signature of addiction has been found. Heilig’s group conceded that some of these points have merit. Their reply still defended the neurobiological basis of addiction, holding that spontaneous remission does not disprove it. Denying the disease view, they warned, shrinks access to health care and treatment, with what they called catastrophic results.
What Does the Disease Model Mean for Recovery?
The 2016 review gives medication a role while the affected circuits heal, with methadone or buprenorphine easing opioid withdrawal and cravings. For alcohol use disorder, naltrexone and acamprosate have shown efficacy.
Behavioural care goes after the faded rewards and conditioned cues covered earlier, with the NEJM authors suggesting that social contact, exercise or other everyday rewards could be rebuilt to compete with the drug. For cue-driven craving, changing one’s circle of friends and staying away from drug-linked places can lower the chance that a learned craving turns into relapse.
Access to that care lags behind need in Canada, where only 48.8% of people aged 15 and older who met criteria for a mood, anxiety or substance use disorder in the past year had talked to a health professional about their mental health. Over a third (36.6%) of that group reported partly or fully unmet needs for care.
Where Addiction Science Is Looking Next
Heilig and colleagues argue that the brain gives rise to addiction as well as to the capacity for behaviour change, which is why they call for more neuroscience research on recovery itself. NIDA’s Adolescent Brain Cognitive Development Study is following nearly 12,000 children from ages 9 to 10, before any substance use, into young adulthood. Tracking children from before their first exposure lets researchers separate brain differences that precede substance use from changes that follow it.
Written by Amelia Turner (ameliaturner7712@gmail.com)
