after joining the study you are assigned to receive either fenebrutinib 400 mg or teriflunomide 14 mg. because the study uses a double‑dummy design, you will also receive matching placebo tablets so that the number of pills taken each day is the same for all participants.

both the active drug and the matching placebo are taken by mouth as a single film‑coated tablet each day.

on the first study day a series of assessments are performed before the first dose is taken. these include a physical examination, collection of blood samples, and magnetic resonance imaging (mri) of the brain to record the initial number of lesions.

questionnaires about the impact of multiple sclerosis on daily life are completed.

you take the assigned study medication and the matching placebo tablet every day, at the same time each day, for the duration of the trial. the treatment period lasts at least 48 weeks.

scheduled visits occur approximately every 4 to 12 weeks (for example at weeks 4, 12, 24, 36, and 48). during each visit a clinician checks for any side effects, measures vital signs, and records any relapses of multiple sclerosis.

blood is drawn at each visit to monitor safety and to measure the level of fenebrutinib in the blood for participants who receive it.

at week 24 a second brain mri scan is performed to evaluate changes in the number of lesions and overall brain volume.

at designated visits (for example weeks 12, 24, 36, and 48) you complete the Multiple Sclerosis Impact Scale (MSIS‑29) to report physical effects of the disease.

at week 48 a final set of evaluations is performed. this includes a physical exam, blood tests, a third brain mri scan, and completion of the MSIS‑29 questionnaire.

the occurrence of any relapses, side effects, or serious adverse events is recorded, and the study medication is stopped.

after the final visit you are no longer required to take the study medication. study staff may provide information about post‑study follow‑up, but no further study procedures are required.