Distinguishing between a mental disorder that is the result of a mental illness or mental retardation and a mental disorder that is the result of substance abuse can be very challenging. While the legal system has long recognized that a mental disorder that is the result of a mental illness or mental retardation may be relevant in determining criminal responsibility, it has been reluctant to adopt a similar rule when criminal behavior was the result of intoxication, even though the impact of alcohol or drugs on a defendant's mental state may resemble that resulting from mental illness or mental retardation.
The primary rationale for this distinction is that intoxication is a voluntary act, the consequences of which are relatively well-known and predictable, and thus unlike mental illness or mental retardation. As a result, the thinking goes, the criminal defendant should not be able to avoid responsibility for criminal behavior that occurred while the defendant was intoxicated. In Virginia, there are two primary exceptions to this rule: the "settled insanity" defense and involuntary intoxication. The Virginia Court of Appeals addressed both of these exceptions.
In the case before the court, the defendant had shot his estranged wife eight times, causing permanent injury. In response to a charge of malicious wounding, the defendant filed a notice that he intended to present a "settled insanity" defense, alleging that his "actions were the result and/or product of a mental disease or defect produced by long-term substance abuse, ... including, but not limited to, alcohol and [X]anax abuse." Prior to trial, the prosecution argued this defense should not be allowed because the defendant conceded that he did not suffer from a permanent mental defect or disease. The defendant acknowledged this his condition had abated after he stopped drinking and using drugs and received treatment for his liver. He argued, however, that it did not matter whether the resulting insanity was temporary, intermittent, or permanent, as long as his long-term substance abuse produced a mental defect or disease that meets the definition of insanity in Virginia.
In reviewing this question, the Virginia Court of Appeals noted that Virginia recognizes two tests by which a defendant can establish the affirmative defense of insanity: (1) the M'Naghten Rule and (2) the irresistible impulse doctrine. Under the M'Naghten Rule, the defendant must show he or she was "labouring under such a defect of reason, from disease of the mind, as not to know the nature and quality of the act he was doing; or, if he did know it, that he did not know he was doing what was wrong." The irresistible impulse defense is available when the defendant's "mind has become so impaired by disease that he is totally deprived of the mental power to control or restrain his act."
The court also noted that voluntary intoxication in Virginia is not a defense to a criminal charge (except in cases of first degree and capital murder where proof of voluntary intoxication may negate the requisite elements of deliberation and premeditation). At the same time, citing a line of cases that dates back to 1871, the court agreed that long-term, chronic, and habitual abuse of alcohol or drugs will support a defense of insanity when such abuse creates a mental defect or disease that meets the requirements of either of Virginia's two insanity tests. …