The Chicago Tylenol murders were a series of poisoning deaths resulting from drug tampering in the Chicago metropolitan area in 1982. The victims had all taken Tylenol-branded acetaminophen capsules that had been laced with potassium cyanide. A total of seven people died in the original poisonings, with several more deaths in subsequent copycat crimes.
https://en.wikipedia.org/wiki/Chicago_Tylenol_murders