The Insanity Defense Among the States

By Linda Sanabria, J.D. | Legally reviewed by Melissa Bender, Esq. | Last reviewed November 28, 2023

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When a criminal defendant can prove they lacked the mental capacity to commit a given crime, they may be found not guilty because of insanity. In these cases, the defendant may receive mental health treatment in an institution and be prevented from leaving if they're considered a danger to society.

Four states (Kansas, Montana, Idaho, and Utah) explicitly don't allow for the insanity defense. In other states, the requirements of the law for proving this defense vary widely. States that allow for the insanity defense use one (or a combination) of the following legal standards:

  • The M'Naghten Rule: Defendant's mental state leaves them unable to distinguish between right and wrong. They do not understand what they did at the time of the offense as a result of mental disease.
  • The Irresistible Impulse Test: Defendant is unable to control their impulses due to a mental disorder, leading to criminal conduct.
  • The Model Penal Code Test: Defendant has an incapacity to act within legal constraints or failed to understand the criminality of their acts due to a mental defect.
  • The Durham Rule: Defendant's mental illness led to the commission of a criminal act, regardless of clinical diagnosis.

State Insanity Defense Laws

States generally follow one of the four legal standards for determining insanity as an affirmative defense against criminal standards, but they often combine these standards or follow their own modified interpretation. The following provides the status of the insanity defense in each jurisdiction.

State Insanity Defense Rules
Alabama The state uses the M'Naghten Rule. The burden of proof is on the defendant.
Alaska The state uses a modified M'Naghten Rule. The burden of proof is on the defendant. A guilty but mentally ill verdict is allowed.
Arizona The state uses a modified M'Naghten Rule. The burden of proof is on the defendant. A guilty but insane verdict is allowed.
Arkansas The state uses a modified Model Penal Code rule. The burden of proof is on the defendant.
California The state uses the M'Naghten Rule. The burden of proof is on the defendant.
Colorado The state uses a modified M'Naghten Rule with the Irresistible Impulse Test. The burden of proof is on the state.
Connecticut The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.
Delaware The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.
District of Columbia The state uses the Model Penal Code rule. The burden of proof is on the defendant.
Florida The state uses the M'Naghten Test. The burden of proof is on the state.
Georgia The state uses a modified version of the M'Naghten Rule. The burden of proof is on the defendant. A guilty but mentally ill verdict is allowed.
Hawaii The state uses the Model Penal Code rule. The burden of proof is on the defendant.
Idaho The state has abolished the insanity defense. The state allows a guilty but insane verdict.
Illinois The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.
Indiana The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.
Iowa The state uses the M'Naghten Rule. The burden of proof is on the defendant.
Kansas The state has abolished the insanity defense.
Kentucky The state uses the Model Penal Code rule. The burden of proof is on the defendant.
Louisiana The state uses the M'Naghten Rule. The burden of proof is on the defendant.
Maine The state uses a modified version of the Model Penal Code rule. The burden of proof is on the defendant.
Maryland The state uses the Model Penal Code rule. The burden of proof is on the defendant.
Massachusetts The state uses the Model Penal Code rule. The burden of proof is on the state.
Michigan The state uses the Model Penal Code rule. The burden of proof is on the state.
Minnesota The state uses the M'Naghten Rule. The burden of proof is on the defendant.
Mississippi The state uses the M'Naghten Rule. The burden of proof is on the state. An acquitted by reason of insanity verdict is allowed.
Missouri The state uses a modified version of the M'Naghten Rule. The burden of proof is on the defendant.
Montana The state has abolished the insanity defense, although a guilty but insane verdict is allowed.
Nebraska The state uses the M'Naghten Rule. The burden of proof is on the defendant.
Nevada The state uses the M'Naghten Rule. The burden of proof is on the defendant.
New Hampshire The state uses the Durham standard. The burden of proof is on the defendant.
New Jersey The state uses the M'Naghten Rule. The burden of proof is on the state.
New Mexico The state uses the M'Naghten Rule with the Irresistible Impulse Test. The burden of proof is on the state.
New York The state uses the Model Penal Code rule. The burden of proof is on the defendant.
North Carolina The state uses the M'Naghten Rule. The burden of proof is on the defendant.
North Dakota The state uses the Model Penal Code rule. The burden of proof is on the state.
Ohio The state uses the M'Naghten Rule. The burden of proof is on the defendant.
Oklahoma The state uses the M'Naghten Rule. The burden of proof is on the state.
Oregon The state uses the Model Penal Code rule. The burden of proof is on the defendant.
Pennsylvania The state uses the M'Naghten Rule. The burden of proof is on the defendant.
Rhode Island The state uses the Model Penal Code rule. The burden of proof is on the defendant.
South Carolina The state uses the M'Naghten Rule. The burden of proof is on the defendant.
South Dakota The state uses the M'Naghten Rule. The burden of proof is on the defendant.
Tennessee The state uses the Model Penal Code rule. The burden of proof is on the state.
Texas The state uses the M'Naghten Rule with the Irresistible Impulse Test. The burden of proof is on the defendant.
Utah The state has abolished the insanity defense, but guilty but mentally ill verdicts are allowed.
Vermont The state uses the Model Penal Code rule. The burden of proof is on the defendant.
Virginia The state uses the M'Naghten Rule with the Irresistible Impulse Test. The burden of proof is on the defendant.
Washington The state uses the M'Naghten Rule. The burden of proof is on the defendant.
West Virginia The state uses the Model Penal Code rule. The burden of proof is on the state.
Wisconsin The state uses the Model Penal Code rule. The burden of proof is on the defendant.
Wyoming The state uses the Model Penal Code rule. The burden of proof is on the defendant.

Discuss Your State's Definition of Legal Insanity With a Criminal Law Attorney

The defense of insanity has been a hot topic of discussion among lawyers and the public for decades, questioning the competency of some defendants and raising reasonable doubt. If you have any questions about someone's mental condition in relation to the insanity defense, get in touch with a local criminal defense attorney as soon as possible. If you're facing a criminal case, it's important to have a strong advocate on your side.

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