Most discussions of the laws regarding driving under the influence (DUI) in Pennsylvania focus on alcohol and chemical testing for blood alcohol content (BAC). The Pennsylvania DUI statute also applies to various “controlled substances,” which includes marijuana and other illegal drugs, as well as certain medications obtained with a valid prescription. In the case of illegal drugs, the mere presence of the drug above certain thresholds is sufficient to establish DUI, regardless of whether the driver is actually impaired. If the driver is under the influence of legally prescribed medications, prosecutors must prove a level of impairment that prevents the safe operation of a motor vehicle.
The Pennsylvania DUI statute identifies three levels of impairment due to alcohol, based on chemical testing within two hours of driving. Pennsylvania’s implied consent statute enables police to obtain breath or blood samples to establish BAC. The DUI statute does not identify specific amounts of other controlled substances but rather focuses on their legality. The determination of whether a drug is “illegal” is based on the schedules established by the Controlled Substance, Drug, Device, and Cosmetic Act, first enacted in 1972. An “illegal” drug, for the purposes of the DUI statute, is any Schedule I controlled substance, any Schedule II or III substances for which the driver does not have a valid prescription, or the metabolites of any of those substances.