The criminal law sometimes allows intoxication to be used as a defense in trial. Legally defined as the disturbance of mental or physical capacity as the result of the introduction of a foreign substance into the body, intoxication can be the cause of an involuntary mental state that may nullify criminal liability for actions committed while intoxicated.
Except in some cases of specific intent, intoxication itself cannot usually be used as a valid criminal defense. If the defendant became voluntarily intoxicated before committing the offense, then the defendant is fully liable for his conduct. It's everyone's responsibility to refrain from conduct that may cause harm to others.
Involuntary intoxication, however, can often be a legitimate defense in most cases of specific and general intent. If the defendant did not intend to place herself in a state of mind where she would become a danger to others, then the mens rea element of her crime comes under serious question. For example, if Sarah's non-alcoholic beverage is spiked with illegal drugs at a party and she becomes intoxicated while driving home, causing her to get into an accident, she may not be liable for her offense if it can be proven that the drugs were introduced to her system without her knowledge. Once evidence has been introduced in a trial proving that the defendant's intoxication was involuntary, the burden of proof rests on the prosecution to demonstrate the contrary. Otherwise, the defendant cannot have formed the culpable mental state necessary to commit her crime, and the defendant will very likely be found not guilty.