Durham rule

"Product test" redirects here. For tests of consumer products, see Product testing.

A Durham rule, product test, or product defect rule is a rule in a criminal case by which a jury may determine a defendant is not guilty by reason of insanity because a criminal act was the product of a mental disease. Examples in which such rules were articulated in common law include State v. Pike (1870) and Durham v. United States (1954). 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 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 witnesses 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, psychiatrists 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. 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

See also

• Insanity defense
• ALI rule
• M'Naghten rules