• Is a premenopausal woman, 18 to 50 years of age (inclusive);

• A diagnosis of uterine fibroids confirmed by imaging or review of medical records and reports heavy menstrual bleeding negatively affecting quality of life. or

• A diagnosis of endometriosis that is associated with moderate to severe pain.;

• If at risk of pregnancy is willing to avoid pregnancy for 4 years (the duration of the treatment period) using nonhormonal methods of contraception.

• Has a negative serum pregnancy test at the screening visit and a negative urine pregnancy test at the allocation visit (or Month 12 if entering from MVT-601-050 \[NCT04756037; SERENE\]);

• In good physical and mental health based on medical, surgical, and gynecological history as well as physical, gynecological, and breast examinations, clinical laboratory test results, and vital sign measurements;

• Has a body mass index ≥ 18 kg/m\^2.