The fact that epigenetic mechanisms underlie adaptation in adult organisms has become clear thanks to an explosion in research into mechanisms by which chromatin and histone modifications impact transcriptional regulation under a variety of environmental insults. These mechanisms have been demonstrated to play a role in drug addiction, as repeated exposure to drugs of abuse induce alterations in histone acetylation, phosphorylation, and methylation levels, as well as DNA methylation levels (Maze and Nestler, 2011; Robison and Nestler, 2011; Wong et al., 2011). In alcoholic patients, a significant increase in global DNA methylation influenced by reduced levels of DNA methyl transferase 3b (DNMT3b) has been reported and a possible subsequent derangement of epigenetic control suggested (Bönsch et al., 2004, 2006). Furthermore, several genomic loci such as nerve growth factor (NGF) and pro-opiomelanocortin gene (POMC) from blood cells and prodynorphin (PDYN) from brain tissue have been found hyper-methylated in human alcoholics (Bönsch et al., 2006; Muschler et al., 2010; Heberlein et al., 2011; Taqi et al., 2011). In this section, we focus on recent studies demonstrating that miRNAs can regulate epigenetic factors
