OBJECTIVES: This placebo-controlled, randomized study evaluated the efficacy and safety of opicapone 25-mg and 50-mg tablets in Japanese levodopa-treated patients with Parkinson's disease and motor fluctuations. METHODS: Japanese adults (n = 437, age 39-83 years) with Parkinson's disease (United Kingdom Parkinson's Disease Society criteria) received opicapone 25-mg (n = 145), opicapone 50-mg (n = 145), or placebo (n = 147) tablets over the double-blind treatment period (14-15 weeks). The primary efficacy assessment was change in OFF-time; secondary efficacy assessments included OFF/ON-time responders (≥1 hour change from baseline), total ON-time, ON-time with and without troublesome dyskinesia, and Unified Parkinson's Disease Rating Scale. RESULTS: The least squares mean (standard error) change in OFF-time from baseline to the last visit was -0.42 (0.21) hour for the placebo group, -1.16 (0.22) hour for the opicapone 25 mg group, and -1.04 (0.21) hour for the opicapone 50 mg group. The percentage of ON-time responders, changes in total ON-time/ON-time without troublesome dyskinesia, and Unified Parkinson's Disease Rating Scale II (at OFF) all showed statistically significant improvements versus placebo for both opicapone tablet doses (P < 0.05). Unified Parkinson's Disease Rating Scale III (at ON) was improved versus placebo in patients who received opicapone 50 mg (P < 0.05). Adverse events were more common in patients treated with opicapone 25 mg (60.0%) or opicapone 50 mg (54.5%) versus placebo (48.3%). The most commonly reported adverse event was dyskinesia (placebo, 2.7%; opicapone 25 mg, 9.0%; opicapone 50 mg, 12.4%). CONCLUSIONS: In Japanese patients, both opicapone 25 and 50 mg were significantly more effective than placebo with no dose-dependent difference in efficacy, and both doses were well tolerated. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.