A Clinical Study to Evaluate the Safety and Efficacy of Elagolix in Participants With Moderate to Severe Endometriosis-Associated Pain

Inclusion Criteria:

- Participant is a premenopausal female 18 to 49 years of age (inclusive) at the time of
Screening.

- Participant has a documented surgical diagnosis (e.g., laparoscopy or laparotomy) of
endometriosis established by visualization within 10 years prior to entry into Washout
or Screening.

- Participant must agree to use only protocol specified rescue analgesics during the
Screening and Treatment Periods for endometriosis-associated pain.

- Participant must have the following documented in the e-Diary during the last 35 days
prior to Study Day 1:

1. At least 2 days of "moderate" or "severe" Dysmenorrhea (DYS) AND either

2. At least 2 days of "moderate" or "severe" Non-menstrual pelvic pain (NMPP) and an
average NMPP score of at least 1.0, OR

3. At least 4 days of "moderate" or "severe" NMPP and an average NMPP score of at
least 0.5.

Exclusion Criteria:

- Participant has chronic pelvic pain that is not caused by endometriosis, that requires
chronic analgesic therapy, which would interfere with the assessment of
endometriosis-related pain.

- Participant is using any systemic corticosteroids for over 14 days within 3 months
prior to Screening or is likely to require treatment with systemic corticosteroids
during the course of the study. Over-the-counter and prescription topical, inhaled or
intranasal corticosteroids are allowed.

- Participant has a history of any major depression or post-traumatic stress disorder
(PTSD) within 2 years of the screening visit or other major psychiatric disorder at
any time.

- Participant has a history of suicide attempts or answered "yes" to questions 4 or 5 on
the suicidal ideation portion of the Columbia-Suicide Severity Rating Scale (C-SSRS)
within the last 1 year at Screening or prior to randomization on Day 1.

- Participant has any history of osteoporosis or other metabolic bone disease or any
condition that would interfere with obtaining adequate Dual Energy X-Ray
Absorptiometry (DXA) measurements

- Screening DXA results of the lumbar spine (L1-L4), femoral neck or total hip Bone
Mineral Density (BMD) corresponding to less than 2.0 or more standard deviations below
normal.

- Participant has either:

1. a newly diagnosed, clinically significant medical condition that requires
therapeutic intervention (e.g., new onset hypertension), that has not been
stabilized 30 days prior to randomization on Day 1 OR

2. a clinically significant medical condition that is anticipated to require
intervention during the course of study participation (e.g., anticipated major
elective surgery) OR

3. an unstable medical condition that makes the subject an unsuitable candidate for
the study in the opinion of the Investigator, (including, but not limited to,
uncontrolled diabetes mellitus, uncontrolled hypertension, epilepsy requiring
anti-epileptic medication, unstable angina, confirmed inflammatory bowel disease,
hyperprolactinemia, clinically significant infection or injury).

- Participant has any conditions contraindicated with use of E2/NETA.