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 Missouri, voluntary intoxication is generally not a defense to criminal charges. The state's legal position is that individuals are responsible for their actions, even if they are under the influence of drugs or alcohol. However, there are exceptions where involuntary intoxication may be considered a defense. Involuntary intoxication can occur if a person is forced to consume a substance or does so unknowingly, and as a result, is unable to understand the nature, quality, or wrongfulness of their actions. In such cases, the defense must prove that the intoxication was indeed involuntary and that it negated the required mental state for the crime. For specific intent crimes, such as attempted murder, a defendant in Missouri may argue that their voluntary intoxication prevented them from forming the specific intent necessary to commit the crime. This is a complex defense and whether it is applicable is typically a question of fact for the jury to determine based on the evidence presented at trial. The statutes governing these defenses can be found in Missouri's criminal code.