High-throughput technologies generating large amounts of individual data besides gene variant information have expanded, permitting investigators to analyze human variation across different omics data types (such as epigenomics and transcriptomics)124. Different tissues and cell types are expected to be more or less informative depending on the specific SUD traits studied. Brain is often the organ of greatest interest (but not necessarily, because peripheral metabolism is, as detailed above, also important). However, study of brain tissue is possible only postmortem, and this entails substantial compromises. As discussed above, analyses of human GWAS results have demonstrated that the exact phenotype studied — substance use, initiation, quantity, physiological dependence, and so on — is critically important. But for deceased subjects, phenotypic information is often limited. Sometimes we find ourselves in the position of needing, for example, to interpret epigenetic findings for subjects who have died of opioid overdose. But were they opioid dependent? Did they overdose accidentally, or did they die of suicide? If the latter, were they opioid-exposed prior to the terminal event? When we study peripheral tissues from living subjects, we
