The "Durham Rule"

A defendant found "not guilty by reason of insanity" (or legally insane) cannot be convicted for crimes committed as a result of certain mental conditions, since willful intent is required for most convictions. State and federal courts use a legal test to determine the mental state of the defendant at the time of the incident if he or she uses the insanity defense. The four main types of tests are the M'Naghten Rule; the Irresistible Impulse test; the Model Penal Code test; and the Durham Rule.

This article discusses the Durham Rule as a legal standard for insanity, which currently is only used in the state of New Hampshire. See Current Application of the Insanity Defense and Status of the Insanity Defense for more information.


According to the Durham Rule, a criminal defendant cannot be convicted of a crime if the act was the result of a mental disease or defect at the time of the incident. It has often been referred to as the "product defect" rule, but does not require a medical diagnosis of mental illness or disorder. Federal courts and all but one state court rejected it for being too broad. For example, drug addicts were able to use the defense to successfully avoid conviction for crimes related to their addiction.

New Hampshire is the only state to still use this rule, but courts have narrowed its interpretation in an effort to limit the defense to only the most serious cases. According to the code section, defendants must prove legal insanity "by clear and convincing evidence."

See The Insanity Defense Among the States to learn more about the standard used in your state.

Origins of the Durham Rule

This rule was first adopted by New Hampshire in 1871. It became more widespread after a 1954 U.S. Court of Appeals decision (Durham v. United States) in which the court found the existing tests for legal insanity inadequate. At the time, insanity was based on either the inability to know right from wrong or the inability to control impulses (also, both tests required a clinical diagnosis of insanity). The court decided that this approach failed to account for certain mentally defective individuals charged with crimes, suggesting the following test instead:

"The question will be simply whether the accused acted because of a mental disorder, and not whether he displayed particular symptoms which medical science has long recognized do not necessarily, or even typically, accompany even the most serious mental disorder."

The case established a new approach in federal and some state courts, but quickly came under heavy criticism because it lacked a clear legal standard of criminal responsibility. For instance, someone who committed a crime related to a gambling addiction could successfully be found not guilty by reason of insanity using the Durham test. Federal and most state courts abandoned this rule in 1972. Today, New Hampshire courts place a fairly strict burden of proof on the defendant when the insanity defense is used.

Get Professional Help With Your Legal Defense From a Lawyer

Insanity defenses are common in popular culture, and in TV and movies the defense often works wonderfully. In the real world insanity defenses are much more complicated than this portrayal would lead you to believe. If you, or someone close to you, has been accused of a crime for which insanity may be a defense, it would be wise to speak with a criminal defense attorney as soon as possible. 

Next Steps

Contact a qualified criminal lawyer to make sure your rights are protected.

Help Me Find a Do-It-Yourself Solution