Drug Craving Explained
Addicts describe three kinds of drug cravings. The first occurs when they begin to feel the effects of withdrawal (though they’re usually in too much denial to recognize that craving and its accompanying anxiety is flirting with detox). The second comes after a first drink or drug, when they experience an almost automatic, instinctive desire for more. The third type is felt by sober addicts after withdrawal and is associated with relapse.
Addiction researchers say all three type of craving result from the development of drug tolerance. Without the dopamine boost provided by drugs, abusers who have developed tolerance suffer a dopamine deficit, resulting in withdrawal and depression. “Eventually, the dopamine circuit becomes blunted; with tolerance, a drug simply pushes the circuit back to normal, boosting the user out of depression, but no longer propelling him or her toward euphoria.”1 Eventually, addicts have to take drugs to maintain an ever-harder-to-achieve post-tolerance “new normal” in which the brain, having adapted to the continuous use of drugs, now requires them to restore the Reward System’s balance. The brain needs drugs to stave off withdrawal instead of just to get high.
The second type of craving, the need for more following a first drink or drug, is compelled to provide the substantial dopamine boost necessary to reach that “new normal” of tolerance. Once addicts start using, the brain cries out for ever more and the deeper the tolerance, the more they need. Addicts in the third and final stage of the disease can’t seem to ever get enough. This is what both addicts and addiction researchers describe as “losing control” over drug use. Once addicts start, they can’t stop.
Once an addict completes withdrawal, both addicts and neuroscientists agree that cravings can result from what addicts call drug-taking triggers and what scientists refer to as “cues.” For an alcoholic, this might be seeing an alcohol commercial, while for a heroin addict a cue might be the sight of a syringe.
Dr. Anna Rose Childress, a psychiatrist at the University of Pennsylvania, has used Positron Emission Tomography (PET) scans to study addiction cues. During PET scans, radioactive elements are introduced into the brain to track neural activity,2 generating a three-dimensional image illuminating brain activity. Her experiments show that drug-taking cues prompt the brain to release a spurt of dopamine. “This increase in dopamine feels similar to a small dose of the drug itself,” she says. Some people report they can taste drugs in the back of their throats, though they haven’t had any.3 “They’re having a miniature high before they even get there,” Dr. Childress says. “…[I]t’s a primer, it’s a seductive pull.”4 This small dopamine spurt triggers the desire for more, similar to what addicts confront following their first drink or drug, a desire so profound it can overpower the best rational intentions. (For more click on Amnesia Explained).
Scientists say the brain’s insula, one of the key structures involved in emotion, plays a significant role in cravings. They discovered this by studying smokers who had damaged insula. Thirteen of nineteen heavy-smoking insula-damaged patients quit, with all but one reporting quitting easily immediately after they suffered brain damage. That is, the damage to their insula destroyed their craving for cigarettes. One said his body “forgot the urge to smoke.”2
Researcher Antoine Bechera, from USC, says an overactive insula generates deep-seated cravings so strong they can overcome the rational. Even smokers who sincerely want to break the habit find their lower-order brain functions, where cravings dwell, outweigh the higher-order cognitive functions that convinced them they should quit.3
However, conquering cigarette cravings in particular and drug cravings in general is more complicated than figuring out how to modify the insula or other brain structure “just so.” Evidence suggests that multiple brain components are involved in several sub-types of craving.
The Duke Center for Nicotine and Smoking Cessation Research performed PET scans on smokers and found three different brain regions involved in cigarette craving, each triggered by different motivations. The thalamus, a key evaluator of sensory information, was activated in subjects who smoked to calm stress. The Limbic “reward” System was activated in those who smoked for relaxation. The area responsible for high-level cognitive function was activated in smokers whose motivation was to manage their weight.4
Accordingly, it seems likely that there are sub-types of cravings for smokers, and addicts in general, each with its own neurological basis.
1. Addiction: A Brain Disease, Not a Moral Lapse, New York Times, Sept. 30, 2003.
2. Cause of Smokers’ Cravings Revealed by Brain Scans;medicalnewstoday.com, March 21, 2007.
3. Cause of Smokers’ Cravings Revealed by Brain Scans;medicalnewstoday.com, March 21, 2007.
4. Cause of Smokers’ Cravings Revealed by Brain Scans;medicalnewstoday.com, March 21, 2007.