Nemolizumab is a subcutaneously administered humanized monoclonal antibody against interleukin-31 receptor A, which is involved in pruritus and inflammation in atopic dermatitis. In phase 2 studies, nemolizumab lessened the severity of atopic dermatitis.In a 16-week, double-blind, phase 3 trial, we randomly assigned Japanese patients with atopic dermatitis and moderate-to-severe pruritus and an inadequate response to topical agents in a 2:1 ratio to receive subcutaneous nemolizumab (60 mg) or placebo every 4 weeks until week 16, with concomitant topical agents. The primary end point was the mean percent change in the visual-analogue scale (VAS) score for pruritus (range, 0 to 100, with higher scores indicating worse pruritus) from baseline to week 16. Secondary end points included the time course of change in the VAS score for pruritus up to week 4, the change in the Eczema Area and Severity Index (EASI) score (range, 0 to 72, with higher scores indicating greater severity), a score of 4 or less on the Dermatology Life Quality Index (DLQI; range, 0 to 30, with higher scores indicating a greater effect on daily life), a score of 7 or less on the Insomnia Severity Index (ISI; range, 0 to 28, with higher scores indicating greater severity), and safety.A total of 143 patients were randomly assigned to receive nemolizumab and 72 to receive placebo. The median VAS score for pruritus at baseline was 75. At week 16, the mean percent change in the VAS score was -42.8% in the nemolizumab group and -21.4% in the placebo group (difference, -21.5 percentage points; 95% confidence interval, -30.2 to -12.7; P<0.001). The mean percent change in the EASI score was -45.9% with nemolizumab and -33.2% with placebo. The percentage of patients with a DLQI score of 4 or less was 40% in the nemolizumab group and 22% in the placebo group; the percentage of patients with an ISI score of 7 or less was 55% and 21%, respectively. The incidence of injection-related reactions was 8% with nemolizumab and 3% with placebo.In this 16-week trial, the use of subcutaneous nemolizumab in addition to topical agents for atopic dermatitis resulted in a greater reduction in pruritus than placebo plus topical agents. The incidence of injection-site reactions was greater with nemolizumab than with placebo. Longer and larger trials are necessary to determine whether nemolizumab has a durable effect and is safe for atopic dermatitis. (Funded by Maruho; JapicCTI number, 173740.).