When endorphin neurotransmitters jump a synapse and land on receptor sites, a pleasurable sensation ensues. Normally the endorphins then detach from the receptor site and return to their presynaptic location. Cocaine attaches itself to the endorphins at the receptor site and prevents their return to the presynaptic site. Thus, (1) the pleasurable effect is maintained and (2) there is a shortage of endorphins when the cocaine is metabolized, resulting in a strong letdown and the urge to use more of the drug.*