Rigellian gene therapy was the only known medical treatment for Taggart's Syndrome, a neurological disorder that affected Humans. Without this treatment, sufferers of the syndrome usually died by the age of twenty.
John Frederick Paxton, leader of the extremist xenophobic group, Terra Prime, suffered from Taggart's syndrome, and took regular injections. Commander T'Pol later pointed out Paxton's hypocrisy in utilizing the treatment, which conflicted with his views of Human purity. (ENT: "Demons", "Terra Prime")