A Clinical Trial to Evaluate Efficacy and Safety of Elagolix Tablets in Women With Moderate or Severe Endometriosis-associated Pain

Inclusion Criteria:

1. Understand the study procedures and methods, voluntarily participate in this trial,and sign the informed consent.
2. Diagnosis of endometriosis by pathological diagnosis or surgery within 10 years priorto screening by laparoscopy or exploratory laparotomy; or diagnosis of endometriosisbased on clinical presentation of endometriosis in combination with previous imagingstudies according to Endometriosis Diagnosis and Treatment Guidelines (Third Edition).
3. Premenopausal female aged 18 and 49 years (both inclusive) with one completemenstruation prior to screening record in the diary for at least 35 days and at leastone complete menstrual cycle before the first dosing.
4. Agree to take only protocol-specified permitted rescue analgesic medications duringthe screening and treatment Periods.
5. Cervical smear is normal or abnormal without clinical significance (acceptance ofnormal cervical smear within 6 months prior to screening; or participant is virgin anddecides not to take cervical smear); ASCUS may be combined with HPV testing. ASCUSparticipants may be included if they are negative for high-risk HPV.
6. Agree to use non-hormonal contraception from signing the informed consent through 1month after last dosing.

Exclusion Criteria:

1. Subjects with a history of sensitivity to elagolix or excipients; or with a knownhistory of serious, life-threatening or significant allergy to any drug.
2. Previous non-responders to GnRH agonist or GnRH antagonist therapy as judged by theinvestigator.
3. Subjects with a history of previous or existing osteoporosis or other metabolic bonedisease; or previous abnormal clinically significant hypocalcemia, hypophosphatemia orhyperphosphatemia; or DXA Z score (subjects < 40 years old) or T score (subjects ≥ 40years old) of lumbar spine (L1-L4), femoral neck or total hip BMD is < -2.0;
4. Subjects with unstable diseases (such as poorly controlled diabetes, poorly controlledhypertension, poorly controlled seizures, unstable angina pectoris, inflammatory boweldisease, hyperprolactinemia, malignant tumors (except basal cell carcinoma of theskin) or severe infection, etc.) unuitable for the study at screening as judged by theinvestigators;
5. Subjects with a history of hysterectomy, oophorectomy, or surgery affecting drugabsorption; or those who plan to undergo the above surgery during the trial;
6. Subjects with a history of major depressive disorder or post-traumatic stress disorderwithin 2 years prior to screening or other major psychiatric disorder at any time (e.g., schizophrenia, bipolar disorder); or history of suicidal behavior orsuicidality; or suicidality as judged by the investigators;
7. Subjects with undiagnosed vaginal and/or uterine bleeding within 3 months prior toscreening;
8. Subjects with other chronic pain syndromes requiring chronic analgesia or otherlong-term treatment that would be expected to interfere with the assessment ofendometriosis-related pain;
9. Subjects with a history of drug or alcohol abuse within 6 months prior to screening;
10. Subjects aged ≥ 40 years with abnormal results of breast ultrasonography during thescreening period or within 1 year prior to screening (BI-RADS classification grade 4and above);
11. Clinically significant gynecological conditions (e.g., any non-malignant cyst > 6 cm,or malignant cyst) by TVU or transrectal ultrasound or transabdominal ultrasound atscreening;
12. Subjects with hepatitis B [HbsAg is positive and detection of HBV-DNA indicates viralreplication], hepatitis C [HCV antibody is positive and detection of HCV-RNA indicatesviral replication], positive syphilis (except specific antibody detection positive,non-specific antibody detection negative and confirmed as inactive infection incombination with clinical judgment), known HIV positive history or HIV positive;
13. Subjects with moderate/severe liver injury caused by previous diseases, or AST or ALTor bilirubin ≥ 2 × ULN at screening;
14. Subjects requiring the use of a prohibited long-acting anesthetic or immediate-releaseanesthetic for more than 2 consecutive weeks for the treatment ofendometriosis-related pain within 6 months prior to screening;
15. Participation in any other interventional clinical trial (including drug and deviceclinical trials) within 1 month prior to screening;
16. Use of any systemic corticosteroids for more than 2 weeks within 3 months prior toscreening or likely to require such therapy during the study (topical, inhaled, ornasal corticosteroids are allowed);
17. Use of GnRH agonists or GnRH antagonists (including participation in clinical trailsof elagolix) within 6 months prior to screening; use of medroxyprogesterone acetate,danazol, aromatase inhibitors within 3 months prior to screening; use of oralcontraceptives, or any hormonal treatment for endometriosis within 2 months prior toscreening; use of Chinese herbal medicine for endometriosis treatment or symptomrelief within 1 month prior to screening;
18. Subjects with IUD or subcutaneous contraceptive implants (the IUD or subcutaneouscontraceptive implants removed more than 30 days prior to screening is allowed);
19. Subjects taking moderate or strong CYP450 3A inducers or OATP1B1 inhibitors within 1month prior to the first dosing;
20. Pregnant or lactating women; or plan to have children during the trial (from signingthe informed consent form to 3 months after using the study drug); or < 6 months afterdelivery; or < 3 months after abortion; or have a positive pregnancy test resultduring the screening period or on the day of randomization;
21. Subjects with increasing risk associated with the study, interference with theinterpretation of study results, or inappropriate as judged by the investigators.