In Oregon, we have the crime of Driving Under the Influence of Intoxicants (DUII). An intoxicant can be alcohol (the most commonly thought of DUII) or a controlled substance.
A controlled substance, in Oregon, is defined as a drug or other substance, or immediate precursor, included in schedule I, II, III, IV, or V of the Federal Controlled Substance Act. Not all drugs are controlled substances. There are some drugs considered “controlled prescriptions,” because they require a prescription from a physician, but are not scheduled under the Controlled Substance Act and therefore are not controlled substances for the purposes of a DUII.
There also are some drugs, such as over-the-counter Benadryl, which may adversely affect your motor functions (i.e. cause drowsiness), but they cannot be the basis for a DUII by a controlled substance. However, such drugs may be considered in conjunction with the use and effects of a controlled substance in determining if someone is under the influence of intoxicants.