The purpose of this prospective, randomized, double-blind, placebo-controlled study was to determine the effect of the administration of sublingual triazolam on the success of the inferior alveolar nerve (IAN) block in patients experiencing irreversible pulpitis. Fifty-eight emergency patients diagnosed with irreversible pulpitis of a mandibular posterior tooth randomly received, in a double-blind manner, an identical sublingual tablet of either 0.25 mg of triazolam or a placebo 30 minutes before administration of a conventional IAN block. Access was begun 15 minutes after completion of the IAN block, and all patients had profound lip numbness. Success was defined as no or mild pain (visual analog scale recordings) on access or initial instrumentation. The success rate for the IAN block was 43% with triazolam and 57% with the placebo, with no significant difference (P = .43) between the 2 groups. For mandibular posterior teeth, triazolam in a sublingual dose of 0.25 mg did not result in an increase in success of the IAN block in patients with irreversible pulpitis. Therefore, when using conscious sedation, profound local anesthesia is still required to eliminate the sensation of pain during endodontic treatment for patients with irreversible pulpitis.