Settled insanity
Settled insanity is defined as a permanent or "settled" condition caused by long-term substance abuse and differs from the temporary state of intoxication. In some United States jurisdictions "settled insanity" can be used as a basis for an insanity defense, even though voluntary intoxication cannot, if the "settled insanity"  negates one of the required elements of the crime  such as malice aforethought. However, U.S. federal and state courts have differed in their interpretations  of when the use of "settled insanity" is acceptable as an insanity defense and also over what is included in the concept of  "settled insanity".

# History
Early English common law  recognized "settled insanity" as a complete defense for a person who is a habitual drunk but is not intoxicated at the time of the offense. A complete defense exonerates the accused and is a verdict of not guilty. Thus  a person meeting the criteria of  "settled insanity" is not considered responsible for his actions. Under the M'Naghten Rules, the first attempt in criminal law to address the issue of a mentally ill defendant,  mentally illness (or insanity) can be used as a defense if the defendant was
unable  to understand the criminal nature of his act  or  was unable to
distinguish right from wrong at that time of the offense. The standard for an insanity defense developed by the American Law Institute requires a showing that the defendant's mental illness prevented him from abiding by the law. Traditionally, under English common law intoxication, no matter to what degree, was not considered grounds for excusing the defendant's criminal behavior. However, over the last half century, there has been a movement toward allowing intoxication as evidence admissible in court to help the jury understand the criminal act and perhaps  use  it as an excuse or a mitigating factor.
Although voluntary intoxication is not considered an excuse for a criminal act, if it can be shown that the defendant was too intoxicated to deliberate or premeditate the wrongful act, (lacking malice aforethought), a defense of diminished capacity, while not excusing the defendant from responsibility for the act, can serve to reduce the charges. Similarly, the plea of temporary insanity (applicable only to charges of murder) can serve to reduce the charges from first degree murder to assault or lessen the   sentence  if it can be shown that the defendant, due to intoxication, acted without deliberation  or reflection (lacking malice aforethought), thus negating specific intent. However, ten states have rejected that specific intent can be negated by voluntary intoxication. Some jurisdictions allow voluntary intoxication in the context of a preexisting mental disorder to qualify for an insanity defense.

# Settled insanity
Over time, as United States court ruling have been refining the insanity defense, the concept of "settled insanity" has been evolving.  Originally, any form of insanity caused by the voluntary use of drugs was not an eligible defense for a criminal offense. The rationale was that any act that results from voluntary behavior, including the voluntary intake of drugs, is choosing to increase the risk of breaking the law.   Most United States jurisdictions now recognize that the long-term voluntary use of an intoxicating substance can cause a stable or "settled insanity" that can serve as a defense to a criminal act, especially if the long-term use exacerbated a preexisting mental condition. For example the concept of "settled insanity" includes  delirium tremens brought on by the abstinence of an alcoholic from alcohol, in contrast to the temporary insanity of intoxication.
California law recognizes "settled insanity" but distinguishes between the effect of long-term use qualifying as insanity and a temporary mental state resulting from recent use of an intoxicant which would not qualify as insanity. Recent rulings have upheld that insanity does not have to be permanent to qualify as a defense of "settled insanity". In a case where a woman with a substance-induced psychosis murdered her mother, expert witnesses testified that the defendant had "personality defects" that predisposed her to psychosis, and that the psychosis was triggered by chronic substance abuse resulting nine months of hospitalization. The defendant was found guilty because the court ruled her insanity was temporary. The Supreme Court of California overturned the lower court's guilty finding, ruling not guilty by reason of insanity, and stating that in a case in which a temporary psychosis occurs in instances other than during episodes of intoxication constitutes settled insanity and qualifies as a complete defense.
In People v. Skinner, the California Supreme Court further specified the criteria for "settled insanity". The person must have a mental illness that is relatively stable over time and not caused solely by the length of time the substance was abused, and must also meet the legal definition of insanity in that jurisdiction.  Thus it appears that the court is stating that a threshold condition for the insanity defense exists when there is a permanent impairment caused by chronic substance abuse in a person with a preexisting mental illness unrelated to substance abuse, but aggravated or set off by voluntary intoxication.
However, a 2007 decision by the Colorado Court of Appeals in People v. Grant upheld a lower court ruling that did not allow expert testimony on the defendant's state of mind due to voluntary intoxication, thus ruling out any possibility that the issue of "settled insanity" might be raised.

# Case example
In Jervon Lamont Herbin v. Commonwealth of Virginia, Herbin appealed his conviction for attempted rape. The facts of the case are that Herbin was temporarily residing with the victim and was on crutches due to a gunshot wound received when he tried to enter his mother's house while on crack cocaine a week before. After requesting the victim to help him put on his socks, he threatened her with a knife and instructed her to take off her clothes. When the victim attempted to resist, Herbin stabbed her several times with the knife. The victim ceased resisting, and after threatening to kill her, Herbin pretended to call for assistance and eventually did call paramedics, giving them a false story regarding the victim's knife wounds.
At his trial Herbin testified that he felt disturbed that day and had no memory of what happened except seeing the victim sitting in a pool of blood. He also testified to numerous stressors, including the gunshot wound, breaking up with his girlfriend, and recent attempts at suicide. He  introduced  extensive evidence of a history of
physical and sexual abuse, drug abuse, and suicide attempts as well as a lengthy hospitalization. Further, he had attended a sex offender treatment program.
Virginia does allow  for a drug induced "settled insanity" as a defense to
crime. However, Virginia  draws a distinction between intoxication and long term substance abuse. In order to qualify for this defense, Herbin was required to provide substantial evidence of the presence of a mental disorder and the connection between it and the substance abuse.   Herbin provided evidence of recent drug abuse and the victim testified that she had provided him with prescription drug, Halcion, and lay witnesses introduced evidence of his behavior on the day the offense was committed.
The appeals court held that a "settled insanity" defense requires substantial evidence of not only long-term and heavy substance abuse, but convincing evidence of a mental disorder that is related to the substance abuse. Although Herbin did provide evidence of substantial drug abuse, he was unable to provide expert witness testimony of a serious mental disorder. The court held that the substance abuse did not serve as evidence for a "settled insanity" defense alone without the link to a mental disorder. Although lay witnesses testified to his behavior, the court held that lay witnesses were not in a position to provide testimony on the issue of "settled insanity". Also, although Herbin did provide an extensive history of drug and sexual abuse,  the court said no evidence showed either of these issues were causes or results of a mental disorder. Therefor the appeals court upheld his conviction.

# Conclusion
In those states allowing a "settled insanity" defense, the expert witness must first determine whether any symptoms of a mental disorder were present at the time of the offense, and if there were, determine if those symptoms were the result of a lasting impairment rather than caused by intoxication no matter how acute. If it can be shown that any existing the mental disorder is lasting or relatively enduring, then the expert must be able to show how the mental illness interfered with the defendant's ability to know the nature and consequences of his behavior and know that his behavior was wrong, or if it impaired his ability to control his behavior.
Aggressiveness, memory lapses and other common symptoms resulting from acute intoxication are not sufficient in themselves to excuse criminal acts. Further, not all psychotic reactions caused by substance abuse result in behavior that can be related to the criminal act in a way that can support an insanity defense. The presence of psychosis does not mean that the criminal act was caused by the psychosis. A relationship must be shown to exist between the psychosis and the behavior of the defendant.

# Footnotes
-  "The Insanity Defense" (PDF). Loyola of Los Angeles Law Review. Retrieved 2007-10-23..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"\"""\"""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{display:none;font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
-  Jump up to: 2.0 2.1 2.2 2.3 2.4 2.5 2.6 "Intoxication and Settled Insanity: A Finding of Not Guilty by Reason of Insanity". Journal of the American Academy of Psychiatry and the Law. 2007. Retrieved 2007-10-23.
-  Jump up to: 3.0 3.1 "Drug and alcohol intoxication: mens rea defenses". American Association of Psychiatry and the Law Newsletter. 1999. Retrieved 2007-10-24. Unknown parameter |month= ignored (help)
-  Jump up to: 4.0 4.1 4.2 "Lawyers' Reports Annotated". Retrieved 2007-10-23.
-  Jump up to: 5.0 5.1 "Drugs, Alcohol and the Insanity Defense" (PDF). hawaii.gov. Retrieved 2007-10-24.
-  "Colorado Court of Appeals -- January 25, 2007 No. 03CA1034. People v. Grant". cobar.org. 2007. Retrieved 2007-10-24. Unknown parameter |month= ignored (help)
-  Jump up to: 7.0 7.1 7.2 7.3 "Jervon Lamont Herbin v. Commonwealth of Virginia". www.courts.state.va.us. Retrieved 2007-10-24.