Prurigo nodularis is a chronic pruritic skin disease with multiple nodular skin lesions. Nemolizumab is a monoclonal antibody targeting the interleukin-31 receptor, which is involved in the pathogenesis of prurigo nodularis.We conducted a 12-week, randomized, double-blind, phase 2 trial of nemolizumab (at a dose of 0.5 mg per kilogram of body weight) administered subcutaneously at baseline, week 4, and week 8, as compared with placebo, in patients with moderate-to-severe prurigo nodularis and severe pruritus. Moderate-to-severe prurigo nodularis was defined as 20 or more nodules, and severe pruritus was defined as a mean score of at least 7 for the worst daily intensity of pruritus on the numerical rating scale (scores range from 0 [no itch] to 10 [worst itch imaginable]). The primary outcome was the percent change from baseline in the mean peak score for pruritus on the numerical rating scale at week 4. Secondary outcomes included additional measures of itching and disease severity. Safety assessments were performed through week 18.A total of 70 patients were randomly assigned in a 1:1 ratio to receive nemolizumab (34 patients) or placebo (36). The initial pruritus score on the numerical rating scale was 8.4 in each group. At week 4, the peak pruritus score on the numerical rating scale was reduced from baseline by 4.5 points (change, -53.0%) in the nemolizumab group, as compared with a reduction of 1.7 points (change, -20.2%) in the placebo group (difference, -32.8 percentage points; 95% confidence interval, -46.8 to -18.8; P<0.001). Results for secondary outcomes were in the same direction as for the primary outcome. Nemolizumab was associated with gastrointestinal symptoms (abdominal pain and diarrhea) and musculoskeletal symptoms.Nemolizumab resulted in a greater reduction in pruritus and severity of skin lesions than placebo in patients with prurigo nodularis but was associated with adverse events. Larger and longer trials are needed to determine the durability and safety of nemolizumab for the treatment of prurigo nodularis. (Funded by Galderma; ClinicalTrials.gov number, NCT03181503.).