Generally, intoxication is not a defense to a crime. If you choose to become intoxicated you may make some poor decisions, even some you would not have ordinarily made. However, if you commit a crime while intoxicated, that alone will not ordinarily provide you with a defense.
In most jurisdictions, voluntary intoxication is not a defense to a crime. But if a person voluntarily consumed a legally obtained and properly used medication or other substance but did not know, nor have reasonably known, that he or she could become intoxicated or impaired, it is an affirmative defense. Voluntary intoxication which results in brain deterioration long-term may form that basis of a viable insanity defense. For most jurisdictions, whether involuntary intoxication provides a defense to the crime depends on whether the crime is a specific intent crime or a general intent crime.
A specific intent crime typically requires that the accused person intentionally committed the act and intended to cause the particular result when committing the act. An individual charged with a specific intent crime must prove that he or she could not have specifically intended to commit the crime because he or she was intoxicated by alcohol or drugs. If the alcohol or drugs were voluntarily consumed, the individual must also prove that he or she did not know and reasonably should not have known that he or she would become intoxicated or impaired as a result of the consumption. It is not a defense if the individual was under the influence or impaired by alcohol or drugs voluntarily and knowingly consumed.
A general intent crime is more common than a specific intent crime. In a general intent crime, the prosecution must prove that the accused meant to do the act that is prohibited by law. It does not matter whether the person accused intended the act to result in the manner that it did, only that the accused intended to commit the act. If the crime is one of general intent, neither voluntary nor involuntary intoxication may be used as a defense.
Using intoxication as a defense, like many aspects of the law, can be tricky. Even knowing whether intoxication is applicable as a defense or figuring out whether you are charged with a specific or general intent crime requires the assistance of a criminal lawyer.