Involuntary intoxication describes a situation where a person becomes intoxicated through no fault or choice of their own, for example where they are drugged, misled about the nature or strength of a substance, or must take prescribed medication that has unforeseen intoxicating effects. It commonly arises in criminal law when assessing criminal responsibility, mens rea and possible defences.Across England and Wales, Scotland, Northern Ireland and Ireland, the concept is recognised primarily through case law rather than detailed statutory definition. Involuntary intoxication may, in limited circumstances, negate the mental element of an offence or support an insanity‑type or automatism defence, particularly where the accused could not reasonably foresee the intoxicating effect.Courts distinguish carefully between involuntary intoxication and voluntary intoxication, especially in offences of basic intent (such as assault) and specific intent (such as murder). The burden on the accused to establish credible evidence of involuntariness is high, and failures to check labels, dosage or warnings will usually be treated as voluntary.Usage and underlying principles are broadly consistent across the UK and Ireland, though doctrinal labels (e.g. automatism, insanity, diminished responsibility) and statutory frameworks differ between jurisdictions.