Intoxication is sometimes a defense.
Neither voluntary nor involuntary were valid defenses at common law.
While voluntary intoxication is still inadmissable as evidence in general intent crimes, many jurisdictions allow it to negate the mens rea element of specific intent crimes.
- It is not constitutionally required that it ever be allowed as a defense however.
Involuntary intoxication is a complete defense if it causes the defendant to become unable to form the requisite mens rea.