Felodesine Chip
From Star Trek : Freedom's Wiki
The felodesine chip is a small poison tablet used by members of the Romulan military to commit suicide. It is usually formed into a small, one-inch orange disk. There is no antidote known to the Federation.
Alidar Jarok committed suicide by ingesting a felodesine chip in 2366. (TNG: "The Defector")
