The figure summarizes results from Table S4 listing systemic and brain-site specific epigenetic manipulations that play a role in operant drug relapse. Mechanisms related to cocaine are in blue, heroin are in red, Meth are in green, alcohol are in yellow, and both cocaine and heroin are in purple. Abbreviations for brain regions: NAc, nucleus accumbens; dmPFC, dorsal medial prefrontal cortex; BLA, basolateral amygdala; LA, lateral amygdala; DS, dorsal striatum. Abbreviations for epigenetic terms are listed in Table S1.