The purpose of this clinical trial is to learn how well ACT-777991 works, how safe it is and how well it is tolerated by adults with non-segmental vitiligo.
The main question this clinical trial aims to answer is:
• Can ACT-777991 help return color to the skin of the face of adults with non-segmental vitiligo?
Researchers will compare ACT-777991 to placebo (a look-alike inactive treatment that contains no medicine) to see if ACT-777991 works to treat non-segmental vitiligo.
Trial participants will:
* Take the trial intervention (either ACT-777991 or placebo) daily for 24 weeks. * Visit the clinic 7 times for check-up and tests.
F-VASI score ≥ 0.3 based on BICR at Screening.
T-VASI score ≥ 5 based on investigator assessment at Screening and Randomization.
Total body surface area (BSA) involvement, including the face, ≤ 50% based on investigator assessment at Screening and Randomization.
Participants must agree not to use therapeutic agents and procedures to treat vitiligo from Screening until Participant Last Visit.
Clinical diagnosis of other forms of vitiligo (e.g., segmental) or other hypo- or depigmentation disorders (e.g., piebaldism, leukoderma, Vogt-Koyanagi-Harada disease, malignancy-induced hypopigmentation).
Any autoimmune disease, except adequately treated thyroid disease.
History of systemic immunotherapy treatment, including JAK inhibitors, for any inflammatory disease in the 12 months prior to Randomization.
History of topical JAK inhibitors for any inflammatory disease in the 6 weeks prior to Screening.