(a) Intoxication that is not self-induced intoxication is an affirmative defense to a prosecution if at the time a person engages in the conduct charged to constitute the offense the person lacks capacity to:
(1) Conform his or her conduct to the requirements of the law; or
(2) Appreciate the criminality of his or her conduct.
(b) As used in this section:
(1) "Intoxication" means a disturbance of a mental or physical capacity resulting from the introduction of alcohol, a drug, or another substance into the body; and
(2) "Self-induced intoxication" means intoxication caused by a substance that the actor knowingly introduces into his or her body and the actor knows or ought to know the tendency of the substance to cause intoxication.