Ku'thei

Ku'thei is a substance that is poisonous to a number of humanoid species, including both Klingons and humans.

Ku'thei was not well known to Federation science in 2367 and Starfleet transporters had not been configured to detect or screen out Ku'thei when transported.

In his campaign of vengeance against his former USS Stargazer (NCC-2893) crewmates, Doctor Carter Greyhorse brought Ku'thei pills on board the USS Enterprise (NCC-1701-D), knowing that the transporter systems would not detect them when he was transported aboard. He attempted to poison both Tricia Cadwallader and Gilaad Ben Zoma with Ku'thei pills. In both cases he was prevented from doing so. In Cadwallader's case Crusher had walked in on him before he could administer the pill. After he had been exposed as the man trying to kill the Stargazer crew members, Greyhorse tried to administer a Ku'thei pill to Ben Zoma, but despite forcing the pill into Ben Zoma's mouth, Greyhorse was interrupted by Doctor Selar, who was able to retrieve the pill before Ben Zoma swallowed the pill.

After Greyhorse was captured, his supply of Ku'thei pills was discovered in his quarters. Both the pills and the other weapons Greyhorse was using were held as evidence by Lieutenant Worf.