From http://www.eurekalert.org/pub_releas...-ana120502.php

There is an intersection between the worlds of drug addiction and dopamine replacement as well as addiction to those replacements. Naltrexone, dextromethorphan, and cannabis have a place in all three.

It seems that NAC may have a role there as well-

"A new approach holds promise for reducing cocaine craving

..."Our studies show that administration of an existing drug – n-acetyl cysteine, which is used to treat cystic fibrosis and several other disorders – reverses the changes in brain chemistry that appear to cause cocaine craving," said David A. Baker, a post-doctoral fellow in the laboratory of Peter W. Kalivas at the Medical University of South Carolina. ..."

"Previous studies have found that cocaine addiction interferes with the levels of the common neurotransmitter glutamate in the nucleus accumbens. Normally, the neurons are bathed in high levels of glutamate, which tends to reduce their sensitivity so that they fire less frequently. When cocaine is withdrawn after repeated exposures, however, glutamate levels plunge to about half their normal level. During the withdrawal stage, injections of small amounts of cocaine produce large increases in glutamate concentrations, but only for short periods"

This sounds much like a possible explanation if one substitutes "dopamine" for "glutamate". And large increases in glutamate for short periods might explain some dyskinesias.