Study halted due to the significant enrollment challenges encountered since its beginning. Screening and enrollment have been impacted by the COVID pandemic and more importantly by changes in the diagnosis and treatment of women with endometriosis.

The primary objective of this study is to demonstrate the efficacy and safety of linzagolix administered orally once daily for 3 months at a dose of 75 mg alone or of 200 mg in combination with add-back hormone replacement therapy (ABT: estradiol (E2) 1 mg / norethisterone acetate (NETA) 0.5 mg) versus placebo, in the management of moderate to severe endometriosis-associated pain (EAP).

This is a prospective, randomized, double-blind, placebo-controlled study to demonstrate the efficacy and safety of linzagolix administered orally once daily at doses of 75 mg alone and 200 mg in combination with low dose ABT (E2 1 mg/NETA 0.5 mg) versus placebo in the management of moderate to severe EAP in 450 women.

Eligible subjects who have completed the 6-month treatment period may enter a separate extension study for 6 additional months of active treatment (no placebo control). Subjects who do not continue in the extension study will enter a 6 month treatment-free follow-up phase.

Key Inclusion Criteria:

The subject must have:

• Her most recent surgical and - if available - histological diagnosis of pelvic endometriosis up to 10 years before screening.
• Moderate to severe endometriosis-associated pain during the screening period.
• Regular menstrual cycles.
• BMI ≥ 18 kg/m2 at the screening visit.

Key Exclusion Criteria:

The subject will be excluded if she:

• Is pregnant or breast feeding or is planning a pregnancy within the duration of the treatment period of the study.
• Is less than 6 months postpartum or 3 months postabortion/ miscarriage at the time of entry into the screening period.
• Has had a surgical history of any major abdominal surgery within 6 months or any interventional surgery for endometriosis performed within a period of 2 months before screening.
• Did not respond to prior treatment with GnRH agonists or GnRH antagonists for endometriosis.
• Has a history of, or known, osteoporosis or other metabolic bone disease.
• Has chronic pelvic pain that is not caused by endometriosis and requires chronic analgesic or other chronic therapy which would interfere with the assessment of endometriosis-associated pain.

Females Only