(1) “Intoxication” means the inability, resulting from the introduction of substances into the body, to exercise control over one's mental faculties.

(2) “Voluntary intoxication” means intoxication caused by substances which the actor knowingly introduces into the actor's body, the tendency of which to cause intoxication the actor knows or should know, unless the actor introduces them pursuant to medical advice or under such duress as would afford a defense to a prosecution for a criminal offense.