Nogatch Hemlock
From Star Trek : Freedom's Wiki
Nogatch hemlock is a substance which is extremely poisonous to humanoids. It has no known antidote.
In 2372, Q gave Quinn Nogatch hemlock so that he could commit suicide. USS Voyager's Doctor stated that the drug was not available in the ship's medical stores, and Lieutenant Tuvok stated that the ship's replicators would not produce it either. (VOY: "Death Wish")
