A Durham rule, product test, or product defect rule is a rule in a

criminal case Criminal procedure is the adjudication process of the criminal law. While criminal procedure differs dramatically by jurisdiction, the process generally begins with a formal criminal charge with the person on trial either being free on bail ...

by which a

jury A jury is a sworn body of people (jurors) convened to hear evidence, make Question of fact, findings of fact, and render an impartiality, impartial verdict officially submitted to them by a court, or to set a sentence (law), penalty or Judgmen ...

may determine a defendant is

not guilty by reason of insanity Not or NOT may also refer to: Language * Not, the general declarative form of "no", indicating a negation of a related statement that usually precedes * ... Not!, a grammatical construction used as a contradiction, popularized in the early 1990 ...

because a

criminal act In ordinary language, a crime is an unlawful act punishable by a state or other authority. The term ''crime'' does not, in modern criminal law, have any simple and universally accepted definition,Farmer, Lindsay: "Crime, definitions of", in Cane ...

was the product of a mental disease. Examples in which such rules were articulated in

common law Common law (also known as judicial precedent, judge-made law, or case law) is the body of law primarily developed through judicial decisions rather than statutes. Although common law may incorporate certain statutes, it is largely based on prece ...

include '' State v. Pike'' (1870) and '' Durham v. United States'' (1954).''Criminal Law - Cases and Materials'', 7th ed. 2012,

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; John Kaplan,

Robert Weisberg Robert I. Weisberg is an American lawyer. He is the Edwin E. Huddleson Jr. Professor of Law at Stanford Law School. Weisberg is an authority on criminal law and criminal procedure, as well as a scholar in the law and literature movement. Educa ...

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,

/ref> In ''Pike'', the Superior Court of Judicature of New Hampshire wrote, "An accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect." Additionally, It is important to note that the insanity defense plea has been removed in a handful of states and left with the "guilt by insane" verdict. These states include, Montana, Idaho, and Utah. The ''Durham'' rule was abandoned in the case '' United States v. Brawner'', 471 F.2d 969 (1972). After the 1970s, U.S. jurisdictions have tended to not recognize this argument as it places emphasis on "mental disease or defect" and thus on testimony by

psychiatrists A psychiatrist is a physician who specializes in psychiatry. Psychiatrists are physicians who evaluate patients to determine whether their symptoms are the result of a physical illness, a combination of physical and mental ailments or strictly ...

and is argued to be somewhat ambiguous. The Durham rule was constantly criticized because of its lack of clear definitions and terms. It is said that the problem with the "product test" was that it gave psychiatric and psychological experts too much influence in a decision of insanity and not enough to jurors. Although an expert witness may testify as to his opinion in a trial, judges are reluctant to allow it when the opinion goes to the ultimate issue of a case, i.e. when the opinion alone could decide the outcome of a case. The product test asked

expert witness An expert witness, particularly in common law countries such as the United Kingdom, Australia, and the United States, is a person whose opinion by virtue of education, training, certification, skills or experience, is accepted by the judge as ...

es to use their judgment in determining whether criminal actions were "'the product' of a mental disease or defect." It is the jury's job to decide whether a defendant's actions were the product of his mental disease or defect. The expert witness' job is to determine whether the defendant possesses a mental disease or defect. Further, often conflicting 'expert witnesses' were put on the witness stand by the prosecution and defense to draw the opposite conclusions regarding the cause of an individual's actions. One of the most significant impacts of the Durham rule was the expansion of the role of psychiatric testimony in criminal trials. Under this rule,

were no longer limited to testifying about whether a defendant knew right from wrong; instead, they were encouraged to explain the nature of the defendant’s mental illness and whether it caused the criminal act. This shift allowed for more nuanced clinical evidence but also led to growing tension between legal and medical professionals. This increased reliance on psychiatric testimony under the Durham rule led to concerns about the objectivity and consistency of insanity defense outcomes. Critics argued that the rule effectively transformed trials into contests between expert witnesses, leaving juries to navigate conflicting opinions. These concerns about fairness, clarity, and consistency in verdicts contributed to the rule's eventual rejection in many jurisdictions. In comparison to other legal standards for insanity, the Durham rule was distinctive in its exclusive focus on causation—specifically, whether the unlawful act was the product of a mental illness. The M'Naghten rule evaluates a defendant’s capacity to understand right from wrong, while the irresistible impulse test addresses whether a person could control their behavior. In contrast, the Durham rule did not require cognitive or volitional impairment, only a causal link. The American Law Institute (ALI) test, adopted by many jurisdictions after the decline of the Durham rule, combines both cognitive and volitional components. It is generally considered a more balanced approach, incorporating psychiatric expertise while maintaining clearer legal standards for juries to apply.

References

See also