Some potential challenges lie in the way of these goals, relating to the diverse nature of substance use disorders themselves, comorbid use patterns, and limitations of current technology. As noted above, smoking is unique in the number and type of toxic exposures it causes to human cells, which may account for our ability to detect to downstream epigenetic changes. In contrast, other substances such as cocaine may cause dramatic changes in behavioral patterns, both acutely and chronically, as well as cause physiologic dependence, but may not cause a robust epigenetic signature detectable by current technology. If so, this may be due to the fact that the mechanism of action of many such substances is mediated by tissue-specific receptors, as opposed to the toxic aromatic compounds found in burnt tobacco products, or alcohol, which is itself a solvent molecule able to penetrate cell membranes throughout the body. However, it is possible that other kinds of epigenetic changes such as histone modification, for which current assays are less advanced, will become detectable as technology improves.
