Also known as: product of mental illness test · product test · Durham test · Durham rule
Written by attorneys · grounded in primary & secondary sources — see below
A causation-based insanity standard that acquits a defendant when the charged offense resulted from a mental disease or defect. The test requires but-for causation between the mental condition and the criminal act.
Priya Prasad, an emergency room nurse, attacked a pharmaceutical representative with trauma shears while experiencing severe postpartum psychosis. Defense experts testified that but for the psychosis and its accompanying delusion that the representative was poisoning patients, Priya would not have committed the assault. The jury acquitted her because the offense was the product of her mental disease.
Perry Pratt, a nuclear plant technician with a documented schizo-paranoid disorder, bypassed three redundant safety interlocks while experiencing fixed delusions that federal agents had installed hidden shutdown mechanisms. He immediately told investigators he acted solely to thwart the conspiracy. The court granted acquittal because the conduct resulted from his mental disease.
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The product test focuses solely on whether the offense resulted from a mental disease or defect through but-for causation. It does not require proof that the defendant lacked capacity to know right from wrong or to control conduct.
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Expert testimony linking the mental disease directly to the criminal act satisfies the requirement when the evidence shows the defendant would not have committed the offense absent the condition. Courts examine motive, timing, and the relationship between the diagnosed condition and the specific actions taken.
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Yes. When evidence shows the defendant would have committed the offense even without the mental disease, such as prior identical conduct driven by production quotas, the but-for link is broken and acquittal is not required.
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Such evidence may support a finding that the conduct was not solely the product of mental disease. When the defendant selects a remote location and times the act to minimize detection, a court may conclude the offense reflected intentional conduct rather than the mental condition alone.
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…a person was so lacking in volition due to a mental defect or illness that he could not have controlled his actions. And the product-of-mental-illness test was used as early as 1870,[^maj-10] and simply asks whether a person’s action was a product of a mental disease or defect.[^maj-11] Seventeen States and the Federal Government have adopted…