Cocaine lowers the levels of a chemical messenger in the brain called enkephalin. Researchers have found the number of enkephalin receptors to be higher in cocaine addicts than nonaddicted people. This is an example of

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Up-regulation refers to an increase in the number of receptors for a particular neurotransmitter due to its decreased availability. In the case of cocaine addiction, the prolonged use of the drug leads to a decrease in enkephalin levels, which triggers the brain to produce more enkephalin receptors to compensate. This can contribute to the cycle of addiction and cravings for more drugs.

Cocaine Lowers the Levels of a Chemical Messenger in the Brain