Promazine was a potent poison of Cardassian origin that killed quickly and caused the body to disintegrate within hours. It was commonly used by Obsidian Order operatives to commit suicide in case of capture.
In 2375, Skrain Dukat, now a priest in the Cult of the Pah-wraiths, planned to use promazine tablets to poison his Bajoran followers, claiming that the tablets would allow them to shed their corporeal existence, though he himself would take a harmless placebo and escape. Kira Nerys foiled his attempt and Dukat was forced to flee. (DS9: "Covenant")
In the mirror universe, Dal Kanril Eleya kept a capsule of promazine in a false back molar in case of capture by Terran forces, fearing their treatment of female prisoners. When she came aboard the USS Bajor as Klingon-Cardassian Alliance liaison officer in 2410, Bajor's chief medical officer Lieutenant (JG) Warragul Wirrpanda insisted on removing it. Wirrpanda stated to the prime universe Kanril Eleya that the Obsidian Order's story that promazine killed painlessly was false: "it feels like your whole head is on fire until you cark it." (Bait and Switch: The Wrong Reflection)