California heroin law prohibits a variety of heroin-related offenses. Two of these that may cause some confusion include California's law against being under the influence of heroin and driving under the influence of heroin.
According to California law, you are under the influence of heroin when your physical and/or mental abilities are impaired in “any detectable manner”. It isn't necessary that you misbehave or engage in any other criminal activity. Simply being under the influence of heroin is a crime in and of itself.
You violate California's law against driving under the influence of heroin when you drive a car after using heroin when the drug has "so far affected the nervous system, the brain, or muscles as to impair to an appreciable degree your ability to operate a vehicle in a manner like that of an ordinarily prudent and cautious person in full possession of his faculties”.
This means that driving under the influence requires a higher level of intoxication than being under the influence. So even if you are caught driving when the officer suspects you are under the influence of heroin, the prosecutor could opt to charge you with being under the influence, since that is an easier charge to prove.
A charge of being under the influence of heroin also potentially allows you the opportunity to participate in a California drug diversion program whereas a driving under the influence charge does not. (Also see our article about the difference between marijuana possession, DUI of marijuana, and driving while in possession of marijuana in California law.)