A Study to Investigate Efficacy and Safety of OG-6219 BID in 3 Dose Levels Compared With Placebo in Participants Aged 18 to 49 With Moderate to Severe Endometriosis-related Pain

Inclusion Criteria:

1. Pre-menopausal females of age 18 to 49 years old (inclusive) at the time of signing Informed Consent (V1).
2. Surgically (laparoscopy or laparotomy) diagnosed with endometriosis
3. Moderate to severe endometriosis-related pelvic pain
4. Regular menstrual cycles
5. Is not expected to undergo a planned gynecological surgery or other surgical procedures for treatment of endometriosis during study participation.
6. Normal breast exam at V1. In participants of ≥40 years mammography or contrast-enhanced breast MRI performed within the last 12 months prior to Screening (V1) without clinically significant abnormal findings.
7. Agree not to participate in another interventional study while participating in the present study.
8. Able and willing to adhere to study procedures, including
9. agree to use 2 forms of non-hormonal contraception throughout the study
10. Must be willing and able to provide signed informed consent before any study-related activities
11. Has demonstrated compliance with ≥75% of eDiary entries
12. Has a negative pregnancy test

Exclusion Criteria:

1. Surgical history of hysterectomy and/or bilateral oophorectomy
2. Chronic pelvic and/or non-pelvic pain not caused by endometriosis that requires chronic analgesic or other chronic therapy
3. Undiagnosed (unexplained), abnormal vaginal bleeding not associated with endometriosis within the past 6 months before screening.
4. Presence of high-risk human papillomavirus (HPV).
5. Has an active sexually transmitted infection (STI) (eg, gonorrhea, chlamydia, or trichomonas).
6. Intends to become pregnant or breast feed during study participation or has a known or suspected pregnancy.
7. History of malignancy (except for basal cell or squamous cell skin cancer) before signing informed consent.
8. History of family history of hereditary abnormal hemoglobin or an enzyme deficiency that can result in methemoglobinemia.
9. Has a medical condition associated with hemolytic anemia
10. Known human immunodeficiency virus infection, and/or acute or active, recurrent/relapsing, or chronic infection (eg, hepatitis A, B, or C virus)
11. Has a clinically significant abnormal ECG or QT interval prolongation
12. Used any medication that is either a sensitive substrate, moderate, or strong inhibitor or inducer of CYP3A4 within 30 days or 10 half-lives (whichever is longer) prior to the planned first day of dosing.