Safety and efficacy of oral ACT-777991 in adults with non‑segmental vitiligo: a randomized, double‑blind, placebo‑controlled Phase 2a trial

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What is this study about?

The condition known as Non-segmental vitiligo is a skin disorder in which patches of skin lose their normal color. The loss is usually widespread and can affect the face and other body areas. The study evaluates an oral tablet containing the investigational drug ACT-777991 compared with a matching placebo.

The aim of the study is to assess the safety of the drug and its ability to restore color to the face. Adults with the condition are randomly assigned to receive either the active tablet or the placebo, and they take the medication daily for about six months. Throughout the study, participants attend regular clinic visits where skin appearance on the face is measured using a scoring system called the F-VASI, and basic health checks are performed.

The scoring system evaluates both how much of the face is affected and how deep the loss of pigment is; a lower score means the skin is regaining its normal color. Safety monitoring includes checking for any side effects, vital signs, and basic laboratory tests. The study ends after the final assessment at the 24‑week visit.

1 randomization

after providing consent, you will be assigned at random to receive either the study medication act-777991 or a matching placebo. the assignment is double‑blind, meaning you and the study staff will not know which one you receive.

2 baseline visit and start of medication

at the first clinic visit (week 0) you will undergo a brief physical examination, vital‑sign check, and baseline laboratory tests. you will also receive a supply of the study tablets.

the tablets are oral film‑coated tablets. each tablet is labeled as containing 0 mg of the active substance; the exact amount is not disclosed because the study is blinded.

you will be instructed to take one tablet by mouth once a day, starting on the day of the baseline visit, and to continue this for 24 weeks.

3 daily medication

every day you will swallow one tablet with water, preferably at the same time each day.

if a dose is missed, you should take it as soon as you remember unless it is close to the time for the next dose; do not take two tablets at once.

4 week 4 clinic visit

four weeks after starting the tablets you will return to the clinic for an assessment.

the investigator will evaluate the facial vitiligo score (f‑vasi) and record any changes.

vital signs, a short set of laboratory tests, and an electrocardiogram (ecg) will be performed.

you will be asked about any side effects or new health problems that have occurred since the last visit.

5 week 8 clinic visit

at eight weeks you will have another clinic visit with the same assessments as at week 4: facial vitiligo score, vital signs, laboratory tests, ecg, and safety questionnaire.

6 week 16 clinic visit

the sixteen‑week visit includes a repeat evaluation of the facial vitiligo score, a total body vitiligo score (t‑vasi), vital signs, laboratory tests, ecg, and a review of any adverse events.

7 week 24 final visit

the last scheduled visit occurs at week 24, marking the end of the 24‑week treatment period.

the investigator will assess both the facial and total vitiligo scores, perform vital‑sign checks, laboratory tests, and an ecg.

all side effects, serious adverse events, and any events that led to early discontinuation will be recorded.

you will return any remaining tablets and receive a summary of the study procedures you completed.

8 post‑treatment safety follow‑up

if you discontinue the medication early because of side effects, you will be asked to attend an additional safety visit to monitor vital signs, laboratory values, and ecg until the study staff determine that you are stable.

Who Can Join the Study?

You must have a doctor’s confirmed diagnosis of non‑segmental vitiligo that is either active or stable for at least three months before screening.
Your facial skin must score at least 0.3 on the Facial Vitiligo Area Scoring Index (F‑VASI), a measurement of how much of the face is affected, as read by an independent reviewer.
Your whole‑body skin must score at least 5 on the Total Body Vitiligo Area Scoring Index (T‑VASI), which measures the overall extent of vitiligo across the body.
The total area of skin affected, including the face, must be 50 % or less of your total body surface area (BSA), as judged by the study doctor.
You must not have stopped, reduced, or changed any vitiligo treatment or procedure just to qualify for the trial, and you must agree not to use any vitiligo medicines or procedures from the time of screening until the final study visit (Patient Last Visit, PLV).
The study accepts both male and female participants who are within the age range allowed by the trial (including children and adults as specified by the study).

Who Cannot Join the Study?

You cannot join if you have been diagnosed with other types of vitiligo, such as segmental vitiligo, or other conditions that cause loss of skin color, like piebaldism, leukoderma, Vogt‑Koyanagi‑Harada disease, or skin lightening caused by cancer.
You cannot join if you have any autoimmune disease (a condition where the immune system attacks the body) except if you have thyroid disease that is well controlled.
You cannot join if you have received systemic immunotherapy (treatment that works throughout the whole body) such as JAK inhibitors for any inflammatory disease within the past 12 months before randomization.
You cannot join if you have used topical JAK inhibitors (creams or ointments that block JAK proteins) for any inflammatory disease within the past 6 weeks before screening.
You cannot join if you have used laser or light‑based treatments (phototherapy), including tanning beds, within the past 8 weeks before screening.
You cannot join if your estimated glomerular filtration rate (eGFR) is less than 90 mL/min/1.73 m², which is a measure of kidney function calculated with the Chronic Kidney Disease Epidemiology Collaboration (CKD‑EPI) creatinine equation.

Where you can join this trial?

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Other Sites

Site Name	City	Country	Status
Prof. MUDr. Petr Arenberger, DrSc.	Prague	Czechia

Trial status

Country	Status	Recruitment Start
Czechia	Not yet recruiting	15.07.2026

Trial locations

ACT-777991 is an experimental oral tablet that is being studied to see if it can help restore color to the skin on the face of adults with non‑segmental vitiligo. In this trial, participants take the tablet by mouth, and researchers compare the amount of new skin pigment that appears with what happens in a group that receives a placebo. The goal is to find out whether the medication can safely and effectively promote facial repigmentation.

Investigated Diseases:

Vitiligo

Non-segmental vitiligo – Non-segmental vitiligo is a chronic skin condition where patches of skin lose pigment, creating white spots. It typically appears symmetrically on both sides of the body and often involves the face, hands, and other exposed areas. The loss of color happens because the pigment‑producing cells, melanocytes, are destroyed or stop working. Over time, new patches may appear and existing ones can enlarge, while some areas may remain unchanged for months. The disease usually progresses slowly, but the speed can differ from person to person. It does not cause physical pain but can affect a person’s appearance.

Trial ID:

2025-524865-25-00

Protocol code:

ID-089B201

Trial Phase:

Therapeutic exploratory (Phase II)

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Safety and efficacy of oral ACT-777991 in adults with non‑segmental vitiligo: a randomized, double‑blind, placebo‑controlled Phase 2a trial

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?