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Those of us who have never smoked or have not suffered from substance abuse don’t always understand why it is so hard to simply stop using a drug that is clearly harmful. A review article in this week’s New England Journal of Medicine discusses this in medical parlance (the neurobiology of addiction) and I thought I would relate some of the highlights.

First the definitions:

Substance-use disorder refers to recurrent use of alcohol or other drugs that cause clinically and functionally significant impairment, such as health problems, disability and failure to meet responsibilities at work, school or home. Depending on the level of severity this disorder is classified as mild, moderate, or severe.

Addiction is the term used to indicate the most severe, chronic state of substance-abuse disorder, in which there is a substantial loss of self-control, as indicated by compulsive drug taking despite the desire to stop taking the drug.

Addictive drugs activate reward regions in the brain by causing a sharp increase in the release of dopamine. But with repeated exposure to the same reward, the dopamine cells stop firing in response to the reward itself and instead fire in an anticipatory response or cue of the stimulus. They predict the pleasure from the delivery of the reward and trigger the craving. The greater the pleasure attributed to the reward or the drug, the greater the effort a person is willing to exert in order to obtain it. While all this is happening, ordinary rewards such as those achieved
through relationships and fulfilling family and social responsibilities lose their former motivational power; they simply don’t release the same potent dopamine as that from anticipation or use of the drug.

Ultimately, all this dopamine release renders the brain’s reward system less sensitive to stimulation. The person with addiction no longer experiences the same degree of euphoria from the drug as they did when they first started it.They are also less motivated by every day stimuli. Their forebrain undergoes changes due to the resetting of the reward system. Reactivity to stress changes and the individual experiences negative emotions in an anti-reward system which is fed by “bad” neurotransmitter substances released in an ongoing stress response. Addiction now causes the individual to take the drug to get some relief from their sense of sadness and negative emotions (dysphoria) that they feel from a constant underlying activation of these “bad” neurotransmitters. The authors state that many addicted individuals continue to take the drug to escape the distress they feel when they’re not intoxicated. The longer they use a drug the worse their dysphoria during withdrawal and this produces a vicious cycle.

There are known factors that increase vulnerability to addiction…These include family history, adolescent exposure (when the brain is not fully developed), exposure to high risk environments such as poor familial and social supports in which there is easy access to drugs as well as certain mental illnesses. Apparently adolescents are most at risk because they are still developing brain function and have underdeveloped neural networks in the frontal brain necessary for adult level judgment. These cortical networks are critical to judgment and self-regulation and don’t fully mature until a person reaches 21 to 25 years of age. (Every parent knows that.)

In their summary, the authors state that the neurobiology of addiction provides a compelling argument for leaving the drinking age of 21 and for increasing the legal smoking age to 21.

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