Intoxication caused by substances which the actor knowingly introduces into his body, the tendency of which to cause intoxication he knows or ought to know, unless he introduces them pursuant to medical advice or under such circumstances as would afford a defense to a charge of crime;
^^^So, involuntary is when (1) D does not know that he's ingested the substance, (2) D knows that he's ingested the substance, but has no reason to believe it's intoxication, (3) D ingests something on medical advice, (4) D ingests something under duress (or similar).
(2) can be understood as: If D is tort negligent about the intoxicating effects of the substance he knowingly ingests, then his intoxication is "voluntary" under this rule. So like if D is given a pill at a party that he believes to be an aspirin, but that a reasonable person would know it's likely to be an intoxicating drug, then D is not going to be given an involuntary intoxication defense.
1. Except as provided in Section 120.3(1)(b), criminal homicide constitutes murder when:
a. it is committed purposely or knowingly; or
b. it is committed recklessly under circumstances manifesting extreme indifference to the value of human life. Such recklessness and indifference are presumed if the actor is engaged or is an accomplice int he commission of, or an attempt to commit, or flight after committing or attempting to commit robbery, rape, or deviate sexual intercourse by force or threat of force, arson, burglary, kidnapping, or felonious escape.
2. Murder is a felony of the first degree [but a person convicted or murder may be sentenced to death, as provided in Section 210.6].