Disinformation in politics, advertising, and mass communications has proliferated in recent years. Few counterargumentation strategies have proven effective at undermining a deceptive message over time. This article introduces the Poison Parasite Counter (PPC), a cognitive-science-based strategy for durably countering deceptive communications. The PPC involves inserting a strong (poisonous) counter-message, just once, into a close replica of a deceptive rival’s original communication. In parasitic fashion, the original communication then “hosts” the counter-message, which is recalled on each reexposure to the original communication. The strategy harnesses associative memory to turn the original communication into a retrieval cue for a negating counter-message. Seven experiments (<i>N</i> = 3,679 adults) show that the PPC lastingly undermines a duplicitous rival’s original communication, influencing judgments of communicator honesty and favorability as well as real political donations.