Inclusion Criteria:  etonogestrel implant users at time of and/or within 21 days of initial use of etonogestrel implant placement must agree not to take additional hormonal therapy during the study trial period  Exclusion Criteria:  within 6 months following vaginal or cesarean delivery within 6 weeks following abortion currently breastfeeding positive pregnancy test contraindications to tamoxifen or estrogen history of thromboembolism undiagnosed abnormal uterine bleeding active cervicitis bleeding disorder use of anticoagulation medications an unwillingness or inability to keep a daily menstrual diary or to follow the study criteria