California Vehicle Code definition of
Drug
CVC Section 312. The term "drug" means any substance or combination of
substances, other than alcohol, which could so affect the nervous
system, brain, or muscles of a person as to impair, to an appreciable
degree, his ability to drive a vehicle in the manner that an
ordinarily prudent and cautious man, in full possession of his
faculties, using reasonable care, would drive a similar vehicle under
like conditions.