Low-Dose Naltrexone in Combination With Standard Treatment in Women With Endometriosis

Inclusion Criteria: * Premenopausal female ages 18 to 45 years old on the day of signing informed consent. * Must agree to use only study-specific analgesic medications during the study and is not known to be intolerant to them. * Diagnosed with endometriosis and has had, within the last 10 years prior to signing the informed consent, surgical diagnosis with direct visualization and/or histopathologic confirmation of endometriosis. * Is not expected to undergo gynecological surgery or other surgical procedures for treatment of endometriosis during the study period. * Agrees to use contraception if not surgically sterile during the entire study. * Patients using oral contraceptives, LARCs and/or GnRH agonists/antagonists for contraception and/or management of endometriosis, with a stable regimen, will be able to continue in the study, however, women using oral contraceptives and GnRH agonist/antagonists will be switched to Norethindrone acetate during the 1-2 week run-in period as prescribed by principle investigator. Exclusion Criteria: * Women that are pregnant, breastfeeding or trying to conceive. * Patients with chronic daily narcotic use and any chronic pain or frequently reoccurring pain condition, other than endometriosis, that is treated with opioids or requires analgesics for more than 7 days per month. * Patients with abnormal liver function tests (greater than 3x normal limit) in the past year or history of liver disease. Routine screening of liver function is not required. * Non-English speaking or inability to read and understand English secondary, in part, to the need to read and report daily results in English. * Undiagnosed vaginal bleeding * Patients with history of opioid, illicit drug or alcohol abuse * Patients currently taking thioridazine * Patients with a history of suicidality * Patients with current or history of unstable depression or other psychiatric disorder who, by PI judgement, are unstable or not well controlled * Known, suspected or history of cancer of the breast * Active deep vein thrombosis, pulmonary embolism or history of these conditions * Active or recent arterial thromboembolic disease (e.g., stroke, myocardial infarction)