Intoxication due to a defendant’s voluntary consumption of drugs or alcohol isn’t usually a defense to criminal charges—but if the intoxication was involuntary, it may be a defense on the basis that the defendant did not understand what he was doing or that what he was doing was wrong. And some states allow a defendant to assert a defense that his voluntary intoxication prevented him from forming the specific intent to commit the crime (attempted murder, for example). But this is a question of fact that the jury will usually determine.

The availability and definition of any defense to criminal charges based on the defendant’s voluntary or involuntary intoxication is usually located in a state’s statutes—often in the penal or criminal code.

In Illinois, voluntary intoxication is generally not a defense to criminal charges. However, under Illinois law, there is an exception where voluntary intoxication can be used as a defense if it negates the existence of a mental state that is an element of the offense, such as specific intent. This means that if a defendant was so intoxicated that they could not form the specific intent required for a particular crime, such as attempted murder, they may raise this as a defense. On the other hand, involuntary intoxication can be a defense if the defendant was placed in a state of intoxication without their consent and as a result, lacked the substantial capacity to appreciate the criminality of their conduct or to conform their conduct to the requirements of the law. The success of an intoxication defense, whether voluntary or involuntary, is a question of fact for the jury to determine based on the evidence presented at trial. These defenses are codified in the Illinois Compiled Statutes within the criminal code.