A Study of Zasocitinib in Adults With Nonsegmental Vitiligo

Vitiligo is a long-term autoimmune condition that causes the skin to lose its color. The body's germ-fighting system (immune system) mistakenly attacks the skin cells (melanocytes) which produce the pigment that gives the skin color (melanin). This leads to the formation of patches of skin with less or no pigment (depigmentation). These patches can occur anywhere on the body. In the nonsegmental form of vitiligo, similar patches occur on both sides of the body (symmetrical patches). The main aim of this study is to learn how safe zasocitinib is, how well it works and how well it is tolerated by adults with nonsegmental vitiligo. The participants will receive the study treatment (either zasocitinib or placebo) for up to 1 year (52 weeks). The placebo looks like the zasocitinib capsule but does not have any medicine in it. Participants who receive placebo at the beginning will change to zasocitinib after about 6 months. During the study, participants will visit their study clinic 11 times.

Inclusion criteria: Participant willingness: 1. Participant is willing and able to understand and fully comply with trial procedures and requirements (including digital tools and applications), in the opinion of the investigator. 2. Participant has provided written informed consent and any required privacy authorization before the initiation of any trial procedures. Disease Characteristics: 3. Participants must have a clinical diagnosis of nonsegmental vitiligo: F-VASI greater than or equal to (\>=) 0.5 and a T-VASI \>= 5 and less than or equal to (\=18 years to \=3 times the Upper Limit of Normal (ULN). 2. Total bilirubin (unconjugated and/or conjugated) ˃1.5 times the ULN. 3. Hemoglobin (Hgb) \