In the Realm of Hungry Ghosts: Close Encounters with Addiction

by Gabor Maté

Why does chronic self-administration of cocaine reduce the density of dopamine receptors? It’s a simple matter of brain economics. The brain is accustomed to a certain level of dopamine activity. If it is flooded with artificially high dopamine levels, it seeks to restore the equilibrium by reducing the number of receptors where the dopamine can act. This mechanism helps to explain the phenomenon of tolerance, by which the user has to inject, ingest, or inhale higher and higher doses of a substance to get the same effect as before. If deprived of the drug, the user goes into withdrawal partly because the diminished number of receptors can no longer generate the required normal dopamine activity: hence the irritability, depressed mood, alienation, and extreme fatigue of the stimulant addict without his drug: this is the physical dependence state discussed in Chapter Eleven. It can take months or longer for the receptor numbers in the brain to rise back to pre-drug use figures.