INTRODUCTION: Stuttering is a speech disorder in which the flow of speech is disrupted by repetitions, prolongation, and blocks of sounds, syllables, or words. No pharmacological treatments are approved for use in stuttering, and the most common form of treatment is speech therapy. This study was designed to assess the safety, tolerability, and effectiveness of pagoclone during 8 weeks of double-blind treatment followed by a 1-year open-label extension in patients who stutter. METHODS: An 8-week, multicenter, parallel-group, 2-arm, randomized (ratio 2:1 pagoclone-placebo), double-blind study with a 1-year open-label extension conducted at 16 US centers, including men and women aged 18 to 65 years who developed stuttering before 8 years of age. Twice-daily dosing with pagoclone (n = 88 patients) or matching placebo (n = 44 patients), with primary and secondary efficacy variables defined a priori, including Stuttering Severity Instrument Version 3 outcomes, clinician global impressions of improvement, and the change in the percentage of syllables stuttered. RESULTS: Pagoclone produced an average 19.4% reduction in percentage of syllables stuttered compared with 5.1% reduction for placebo. During open-label treatment, a 40% reduction in the percent syllables stuttered was observed after 1 year of treatment with pagoclone. The most commonly reported adverse event during double-blind treatment was headache (12.5% pagoclone patients, 6.8% placebo patients). DISCUSSION: Pagoclone was effective in reducing symptoms of stuttering and was well tolerated. In light of its favorable tolerability profile, as well as consistency of effects across multiple efficacy variables, pagoclone may have potential as a pharmacological treatment of stuttering. LIMITATIONS: The main limitation of this study was the adequacy of the number of subjects who participated because this study was conducted as a pilot investigation. Furthermore, as this condition waxes and wanes, the assessment of stuttering within the clinic setting may not be an adequate reflection of the stuttering of the patients within the community.