Inclusion criteria:
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.
Participant has provided written informed consent and any required privacy authorization before the initiation of any trial procedures.
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 (<=) 50 at screening and Day 1.
Age and Reproductive Status: Participant is aged >=18 years to <=75 years old at the time of consent.
Participant meets the following birth control requirement: An individual with potential for pregnancy who is now of nonchildbearing potential with laboratory confirmation of postmenopausal status; or an individual with potential for pregnancy who if sexually active with a nonsterilized individual who produces sperm, agrees to use a highly effective method of contraception from the signing of informed consent throughout the duration of the trial. The use of effective contraception will be required for assigned male sex at birth participants.
Exclusion Criteria:
Participant has segmental vitiligo (including mixed vitiligo) or any other congenital or acquired cause of hypopigmentation or depigmentation that could interfere with the diagnosis or assessment of nonsegmental vitiligo.
Participant has >50 percent (%) leukotrichia on the face or >50% leukotrichia of the body (includes the face), within the skin affected by vitiligo.
Participant requires immunomodulatory or immunosuppressive systemic treatment, other than nonsteroidal anti-inflammatory drugs, during the trial period for an immune-related disease (for example, inflammatory bowel disease).
Participant has a history of phototherapy (including, but not limited to, broadband Ultra-Violet [UV]-B, narrowband UV-B, psoralen and UV-A, excimer or other laser therapy, or tanning booth use) within 8 weeks before Day 1. Use of sunscreen products and protective apparel is recommended when sun exposure cannot be avoided.
Participant has concomitant comorbid skin condition that, in the opinion of the investigator, would interfere with the trial assessments.
History of any depigmenting or bleaching treatment for vitiligo or other skin disorder (for example, monobenzone or phenol).
History of any surgical treatments for vitiligo.
History of recent or progressive undiagnosed hearing loss.
Recent/Concurrent Infectious Disease Exclusions.
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.
There may be a higher treatment burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at a hospital or clinic. The effect of the treatment will be checked by medical assessments, blood tests, checking for side effects and completing questionnaires
As a courtesy, patients will receive $100 for each in-person visit and $150 for the Week 24 and Week 52 visits.