The Medical Examiner of Virginia (ME) dataset and the Virginia Department of Forensic Science Driving Under the Influence of Drugs (DUI) datasets were used to determine whether people have the potential to develop tolerances to diphenhydramine, cocaine, oxycodone, hydrocodone, methadone, and morphine. These datasets included the years 2000-2004 and were used to compare the concentrations of these six drugs between people who died from a drug-related cause of death (of the drug of interest) and people who were pulled over for driving under the influence. Three drug pattern groups were created to divide each of the six drug-specific datasets in order to compare concentrations between individuals with the drug alone, the drug and ethanol, or a poly pharmacy of drugs (multiple drugs). An ANOVA model was used to determine if there was an interaction effect between the source dataset (ME or DUI) and the drug pattern groups. For diphenhydramine and cocaine, an interaction was statistically significant, but for the other drugs, it was not significant. The other four drug-specific datasets showed that the DUI and ME were statistically significantly different from each other, and all of those datasets except for methadone showed that there was a statistically significant difference between at least two drug pattern groups. Showing that all of these datasets showed differences between the ME and DUI datasets did not provide sufficient evidence to suggest the development of tolerances to each of the six drugs. One exception was with methadone because there were 14 individuals that had what is defined as a "clinical 'lethal' blood concentration". These individuals provide some evidence for the possibility of developing tolerances.The main outcomes of this study include suggesting changes to make to the ME datasets and the DUI datasets with regard to the way data is kept and collected. Several problems with the fields of these datasets arose before beginning the analysis and had to be corrected. Some of the changes suggested are currently being considered at the Virginia Office of the Chief Medical Examiner as they are beginning to restructure their database.