Extension to Study on Efficacy and Safety of Linzagolix for the Treatment of Endometriosis-associated Pain

Inclusion Criteria: The subject must have: * completed the 6-month treatment in the main study * agreed to continue to use only the analgesic rescue medication permitted by the protocol during the Treatment and Follow-up Periods * agreed to continue to comply with the requirements of the study protocol for the duration of the extension study Exclusion Criteria: The subject will be excluded if she: * is pregnant or breast feeding or is planning a pregnancy within the duration of the of the study (including the Follow-up Period) * likely to require treatment during the study with any of the restricted medications * has any other clinically significant gynecologic condition identified during the main study on transvaginal ultrasound (TVUS), on endometrial biopsy or at the manual breast examination, which might interfere with the study efficacy and safety objectives * meets any of the main study discontinuation criteria