California laws make it illegal to drive while impaired by either a drug or alcohol. The term “drug” is defined by Veh C §312 as any substance or combination of substances, other than alcohol, that could affect the nervous system, brain, or muscles of a person as to impair, to an appreciable degree, his or her ability to drive a vehicle in a prudent and reasonable manner. It does not have to be an illegal substance. It is no defense to a charge of driving under the influence of any drug or the combined influence of alcohol and any drug in violation of California Vehicle Code section 23152 or 23153 that the defendant is or has been entitled to use the drug under state law.
For example, in one case a person was convicted for driving under combined influence of alcohol and insulin. The critical issue is whether the defendant was under the influence. In another case a driver was convicted for DUI when his driving ability appreciably impaired by methamphetamine use based on failed sobriety tests and anxious, agitated, and paranoid mental state
Actual notice of each drug that constitutes a basis for prosecution under state law is not required if a person is reasonably made aware of the proscribed conduct, in other words, impaired driving ability resulting from the ingestion of some substance, For example, one Court found that it was legal error to dismiss charge against defendant based on his consumption of Kava.
Lastly, the actual criminal complaint or citation need not specify particular drug, it is enough that the allegation is raised.