● Modified the rescue therapy permitted for endometriosis-associated pain in Austria, Czech Republic, Hungary, and Spain to allow the use of a combination product containing tramadol 37.5 mg and acetaminophen 325 mg. ● Revised the list of protocol signatories in Appendix B.

● Updated the Overall Study Design and Plan section to reflect the revised approximate number of sites planned for the study, the clarification of pregnancy testing around timing of Day 1, and the expanded Screening Period based on cycle length changes. ● Modified the following key inclusion criteria: ○ Expanded the endometriosis clinical laparoscopic diagnosis window to 10 years. ○ The menstrual cycle window was expanded, and only 1 menstrual cycle would be required to proceed to the Screening Period. ○ Expanded the window during which 2 menstrual cycles were required to occur in order to proceed to the Treatment Period, Day 1. ○ Clarified conditions that would interfere with obtaining adequate DXA measurements ○ Defined which analgesics were to be used in each participating country ● Modified the following key exclusion criteria: ○ Clarified that the use of any known inducers of CYP3A was prohibited within 1 month prior to Day 1. ○ Updated the description of major psychiatric disorders that would result in subject exclusion and expanded to include post-Traumatic stress disorder. ● Updated the Table of Prohibited Medications to indicate that one time use of Cytotec was allowed with the endometrial biopsy procedure required for the study. ● Updated the Table of Permitted Rescue Therapy for endometriosis-associated pain to allow the combination hydrocodone/acetaminophen with 300 mg of acetaminophen since the 300 mg and 325 mg formulations are considered to be equivalent and add the opioids analgesics used in Canada. ● Revised rescue therapy to allow the use of both protocol allowed rescue analgesics simultaneously. ● Updated the Study Procedures Section to describe the Pap test results required for enrollment in the study, and to clarify premedication use for the endometrial biopsy procedure. ● Updated details related to the interim analysis based on the Sponsor's decision regarding the timing of the start of the second pivotal study.

(continued) ● Changed the purpose of the interim analysis based on internal decision to start the second pivotal study with the current elagolix data available at the time.

● Updated the Overall Study Design Plan to clarify Month 6 Treatment visit was Day 1 of extension Study M12-821. ● Revised entry criteria to: ○ Clarified Screening criteria for documentation of menstrual cycles and intervals, malignancy, suicide, use of corticosteroids, and types of investigational studies and products; ○ Updated Pap Test to include biopsy with colposcopy; ○ Clarified use of QTcF or QTcB to evaluate QT interval of 12-lead ECG. ● Added procedures required to be conducted if an additional study drug kit(s) was dispensed at Study Day 168 ± 5 days. ● Updated ECG section to add QT interval correction formula.

● Updated Screening, Treatment, and PTFU Period study activities to further describe physical examination and pregnancy testing requirements, as well as assessment of vital signs and ECGs. ● Added criteria for consideration of clinically significant BMD changes as AEs ● Updated Management of BMD Loss at Month 6 to capture < 8% BMD in the femoral neck as being eligible for participation in the extension study.