Promazine was a substance developed by the Cardassians. The substance was used by agents of the Obsidian Order to commit suicide if captured. Promazine caused the bodies of those who ingested it to rapidly break down into dust within a few hours of death, making it impossible to identify the body.
In 2375, Skrain Dukat attempted to have the members of the Cult of the Pah-wraiths commit mass suicide with promazine. Dukat intended to take a harmless substance disguised to look like a promazine pill. Because the bodies of the cultists would've broken down, it would've left the Federation to assume that he had committed suicide, and that his body was among the mounds of dust that the Federation would've discovered. This mass suicide was prevented by Kira Nerys, and the cult disbanded while Dukat was forced to flee. (DS9 episode: "Covenant")