The Fruit of the Poisonous Tree in IP Law

32 Pages Posted: 10 Nov 2016

Date Written: November 9, 2016


If a police officer searches my home illegally and finds evidence of a crime there, the criminal law suppresses not only that evidence, but evidence derived from the search that was not itself found illegally. This doctrine is known as the “fruit of the poisonous tree.” The animating principle of the fruit of the poisonous tree doctrine is but-for causation: if you had not violated the law, you wouldn’t have found the evidence, and so you wouldn’t have followed whatever investigative path was triggered by the finding of that evidence. The newly discovered evidence – the fruit – is tainted by the poison of the illegal search.

Civil law also concerns itself with chains of causation, both in determining liability and in ordering relief. But civil does not apply the logic of the fruit of the poisonous tree to chase down every consequence of a wrong. Tort law, for example, requires proof not only of but-for causation but also that the defendant was a sufficiently proximate cause of the injury. Plaintiffs can recover for some (but not all) unforeseeable consequences. And while remedies law generally tries to return plaintiffs to their rightful position, compensating them for injuries and giving them what they could have expected to receive absent the wrong, it also limits both who can obtain compensation and the sort of thing for which they can be compensated.

Intellectual property (IP) regimes in particular struggle with causation issues in one important set of cases: defendants who infringe an in IP right in the course of making a product that does not itself infringe that right. Suppose, for instance, that I copy your song onto my laptop in order to make my own song that samples yours. Depending on how much I use, the final song I release may not infringe your copyright, but intermediate versions of my song might, as might the original copy. Or suppose I use a patented microscope without permission to make a scientific discovery that turns into a new drug. The drug doesn’t infringe the patent, which is, after all, on a microscope, not a chemical. But the act of research might infringe. Or I might steal your product to figure out how it works, not so that I can copy it but so I can make a one that works a different way. My final product doesn’t incorporate your secret, but I used my ill-gotten knowledge of your product to get there.

IP law is all over the map in dealing with such cases. Some IP regimes, like trade secret law, apply the fruit of the poisonous tree logic, allowing the plaintiff to recover not only for the profits the defendant made from secrets she actually stole and used but also for the profits of any product that resulted from the use of those secrets. It will also grant a “head-start” injunction against even non-infringing products. Copyright law, by contrast, does not permit a plaintiff either to obtain an injunction or to recover damages against non-infringing final products. Patent law is somewhere in between, refusing to enjoin non-infringing products but leaving the door open to reach-through royalty claims.

It is not clear that these differences reflect any considered judgment about when IP law should prevent or punish the making and sale of non-infringing products tainted by infringement in the process of creation. In this article, I offer a cohesive way to think about the fruit of the poisonous tree in IP law. Whether IP remedies should extend to tainted but non-infringing products should be a function of the mental state of the infringer, the likelihood that infringement will be detected, and the contribution made by the final, non-infringing product. Balancing those three factors won’t necessarily lead all IP regimes to treat the fruit of the poisonous tree in the same way. But it does both explain and suggest some needed reforms to the current legal rules.

Suggested Citation

Lemley, Mark A., The Fruit of the Poisonous Tree in IP Law (November 9, 2016). Stanford Public Law Working Paper No. 2867099. Available at SSRN: or

Mark A. Lemley (Contact Author)

Stanford Law School ( email )

559 Nathan Abbott Way
Stanford, CA 94305-8610
United States

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