Rakghoul serum

The rakghoul serum functioned as a cure for the rakghoul plague, a disease that transformed individuals into rakghouls upon infection.

During the time of the Jedi Civil War, Republic scientists successfully created a sample of this serum. This sample was then reproduced thousands of times with the purpose of healing the Outcasts during the Republic's efforts to restore Taris. The Republic established a base within the Upper City, which served as both the central hub for restoration activities and the laboratory where the scientist refined the cure. However, the Sith armada took notice of the planet and launched an invasion. After forcing the Republic to withdraw, the Sith seized control of the base. Sith troopers then utilized samples of the rakghoul serum while patrolling the Undercity, in search of the crashed Republic escape pods from the destroyed Endar Spire. The Sith's numerous encounters with rakghouls led to a depletion of their serum supply by the time Revan arrived in the Undercity, although some troopers who had been killed still possessed serum samples on their bodies.

In his efforts to escape Taris, Revan discovered a sample of the serum within the Undercity and entrusted it to Zelka Forn, a doctor located in the Upper City. Zelka Forn then synthesized the serum, providing it to all those infected, and gave a substantial quantity to Esala, the healer of the Outcasts, who then used it to treat the infected Outcasts as they journeyed to the Promised Land. Upon reaching the Promised Land, they found it devastated. The buildings, resources, and defenses had been destroyed by Sith bombings. Lacking defenses, the Outcasts remained vulnerable to rakghoul attacks, but the serum helped to manage the spread of the disease. However, the rakghouls continued to evolve, and over several generations, they developed an immunity to the serum's effects. With no means to combat the spread of the rakghoul disease, and surrounded by a bombed-out and diseased world, the Outcasts were ultimately eradicated.

Around the year 3643 BBY, the rakghoul serum was rediscovered by pirates, who located a sample of it within Zelka Forn's long-abandoned secondary medical facility in the Undercity. The serum was subsequently given to a Jedi, and eventually made its way into the possession of a Republic doctor. However, the rakghouls had developed an immunity to the serum even before the Outcasts had been wiped out, rendering it virtually ineffective over three centuries later. The creation of a new serum was necessary, which required infecting a new person to produce new antibodies. These antibodies would then be analyzed and synthesized. A subject was deliberately infected, the antibodies were extracted, a new and improved serum was produced, and once again, it was manufactured in large quantities.