Drug Induced Genes
In a recent study, scientists looked at the effects of habit-forming drugs on the genomic level in mice. The compared the effects of nicotine, methamphetamine, ethanol, cocaine, morphine, and heroin on gene expression. The reason for such a study is that these are among the substances that activate intracellular pathways in the brain reward system. The gave minor amounts of each drug to the mice and applied whole-genome microarray over various time periods of 1, 2, 4, and 8 hours. Through this study, they were able to identify 42 different drug responsive genes that could be grouped into two groups: activity-dependent transcripts like those seen through subjection of psychostimulants and opioids, and those controlled by the release of steroid hormones such as ethanol and opioids. The study revealed that although these drugs that are often abused are very different substances they display a lot of the same genomic markers for addiction.
This means that we are beginning to understand the addiction process better and better with each study, and that we are getting more information that can help guide physicians toward information such as who might be more predisposed to addiction than another person. Also, with such information, we can combat the effects of addition more effectively. If we can understand that specific genomic markers are "turned on" when an addictive substance is allowed into the body, we can help minimized the effects by dialing down the effects. This is very beneficial toward a disease than many people suffer with, whether by their own choices or post-operative medicinal addiction, or any other reason that a person might become addicted to a certain substance. Because we are getting closer to truly understanding this process, we can help all of these people deal with their addiction, and break them of the habit.

http://genomebiology.com/2010/11/5/R47