California Code, Penal Code - PEN § 29.4

(a) No act committed by a person while in a state of voluntary intoxication is less criminal by reason of his or her having been in that condition. Evidence of voluntary intoxication shall not be admitted to negate the capacity to form any mental states for the crimes charged, including, but not limited to, purpose, intent, knowledge, premeditation, deliberation, or malice aforethought, with which the accused committed the act.

(b) Evidence of voluntary intoxication is admissible solely on the issue of whether or not the defendant actually formed a required specific intent, or, when charged with murder, whether the defendant premeditated, deliberated, or harbored express malice aforethought.

(c) Voluntary intoxication includes the voluntary ingestion, injection, or taking by any other means of any intoxicating liquor, drug, or other substance.