OBJECTIVE To evaluate and compare the efficacy and safety of three doses of sodium oxybate and placebo for the treatment of narcolepsy symptoms. METHODS A multicenter, double blind, placebo-controlled trial. METHODS N/A. METHODS Study subjects were 136 narcolepsy patients with 3 to 249 (median 21) cataplexy attacks weekly. METHODS Prior to baseline measures, subjects discontinued anticataplectic medications. Stable doses of stimulants were permitted. Subjects were randomized in blinded fashion to receive 3, 6, or 9 g doses of sodium oxybate or placebo taken in equally divided doses upon retiring to bed and 2.5-4 hours later for 4 weeks. RESULTS Disease symptoms and adverse events were recorded in daily diaries. The primary measure of efficacy was the change from baseline in weekly cataplexy attacks. Secondary measures included daytime sleepiness using the Epworth Sleepiness Scale (ESS), inadvertent daytime naps/sleep attacks and nighttime awakenings. Investigators assessed changes in disease severity using Clinical Global Impression of Change (CGI-c). Compared to placebo, weekly cataplexy attacks were decreased by sodium oxybate at the 6 g dose (p=0.0529) and significantly at the 9 g dose (p=0.0008). The ESS was reduced at all doses, becoming significant at the 9 g dose (p=0.0001). The CGI-c demonstrated a dose-related improvement, significant at the 9 g dose (p=0.0002). The frequency of inadvertent naps/sleep attacks and the nighttime awakenings showed similar dose-response trends, becoming significant at the 9 g dose (p=0.0122 and p=0.0035, respectively). Sodium oxybate was generally well-tolerated at all three doses. Nausea, headache, dizziness and enuresis were the most commonly reported adverse events. CONCLUSIONS Sodium oxybate significantly improved symptoms in patients with narcolepsy and was well tolerated.