In this study, researchers will learn how BIIB141, also known as omaveloxolone or SKYCLARYS®, moves through the body. This is a drug available for doctors to prescribe for patients with Friedrich's Ataxia. But, this drug has not yet been tested in women who have recently given birth and are breastfeeding or pumping milk for their babies. So, researchers do not know how much of the drug could be passed on to babies through the breastmilk of mothers who may take BIIB141.

The main objective of this study is to learn how a single dose of BIIB141 is processed in both the breastmilk and in the blood of healthy women who are breastfeeding.

The main question researchers want to answer in this study is:

• How does BIIB141 move from the blood into the breastmilk?

Researchers will also learn more about:

• How BIIB141 moves through the blood
• What dose of BIIB141 a baby may get from the mother's breastmilk
• Any medical problems the participants have during the study

This study will be done as follows:

• Participants will be screened to check if they can join the study. The screening period will be up to 28 days, after which participants will check into their study research center.
• Participants will take a single dose of BIIB141 as a tablet by mouth on Day 1.
• Participants will remain at their study research center for 6 days. During this time, the participants will be provided with an electric breast pump. This is so that the researchers can collect breastmilk samples before and after the participants take BIIB141. The researchers will also collect blood samples.
• After leaving the study research center, the participants will return every 2 days for the next 10 days for more tests and checkups.
• Finally, there will be a follow-up with a "lactation consultant" up to 30 days after each participant's last study visit. This is someone who can help participants with breastfeeding or pumping.
• Each participant will be in the study for up to 2.5 months.

Key Inclusion Criteria:

• Lactating female 18 to 45 years of age.
• Has given birth to an infant of at least 37 weeks' gestation.
• Is at least 6 weeks postpartum by Day 1.
• Body mass index at screening between 18.0 and and < 35.0 kilograms per meter square (kg/m^2), inclusive.
• Is willing to discontinue breastfeeding their infant from check-in (Day -1) through 19 days after dosing.
• Has never taken omaveloxolone.

Key Exclusion Criteria:

• History of any clinically significant cardiovascular, endocrine, gastrointestinal, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, dermatologic, neurologic, psychiatric, or renal disease, or other major disease, as determined by the Investigator.
• Clinically significant (as determined by the Investigator) 12-lead electrocardiogram (ECG) abnormalities.
• History of, or positive test result at Screening for, human immunodeficiency virus.
• Chronic, recurrent, or serious infection (e.g., pneumonia, septicemia), as determined by the Investigator, within 90 days prior to Screening or between Screening and Day -1.
• Presence or history of hypotension or hypertension.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.

In accordance with Biogen's Clinical Trial Transparency and Data Sharing Policy on https://www.biogentrialtransparency.com/