Ulic Qel-Droma receives an injection of Sith poison from Satal Keto.
Sith poison was a type of biological weapon, a creation born from the practices of Sith alchemy. When a sufficient amount of this toxin entered a person's system, it amplified their feelings of rage. Functionally, it acted more like an infection, establishing itself within the host's body. This, in turn, initiated chemical processes that rapidly weakened the victim's ability to resist the seductive influence of the dark side of the Force. Without intervention by potent Jedi abilities, the poison could prove lethal, and even with such intervention, its lingering effects were highly probable.
Sith poison could be delivered through ingestion or by medical means, typically using a syringe; both methods resulted in a swift onset of effects on the target. It could even be applied directly to the mucous membranes of an existing wound.
Once introduced into the body, the poison is absorbed at a molecular level. It then feeds on the individual's anger, pulling them closer to the dark side. The person's judgment deteriorates, and they eventually succumb to such intense rage that they begin to involuntarily unleash the dark side.
The use of Sith poison was exceedingly uncommon, restricted to only the most skilled Sith alchemists. The creation of the infusion demanded a significant expenditure of the alchemist's own dark side energy, making it a challenging process. However, once completed, the toxin provided the alchemist with a formidable weapon to deploy against any unsuspecting Jedi.
Shortly before the events of the Great Sith War, the Krath leader, Satal Keto, used a syringe to inject Ulic Qel-Droma, a Jedi Knight, with Sith poison. This occurred when Ulic arrived at Cinnagar disguised as a fallen Jedi. Qel-Droma immediately experienced the full force of the poison, involuntarily unleashing the dark side with such force that he shattered the Krath torture device that held him captive. From that moment forward, Qel-Droma suffered from uncontrollable outbursts, ultimately leading him to murder his own brother, Cay Qel-Droma. The sudden shock of Cay's death severed the dark side's hold over Ulic, and ended the torment inflicted by the poison.
During the Galactic Civil War, the Dark Jedi Thaum Rystra employed Sith sorcery to attach stingers to the lekku of the Twi'lek Desvin Tor'thal, which were capable of firing Sith poison.
Sith poison made its debut in the Star Wars: Tales of the Jedi - Dark Lords of the Sith story arc. It served as one of several narrative tools used to develop the story of Ulic Qel-Droma's descent into the dark side. Later, it was further detailed in The Dark Side Sourcebook, a supplementary resource for the Star Wars Roleplaying Game.