• Female with surgically confirmed endometriosis diagnosed by laparoscopy
• Using consistent hormonal therapy for endometriosis for at least 2 months (combination hormonal contraceptives or progestin-only therapy)
• Current pelvic pain with a score of 3 or higher on the Visual Analog Scale for at least 2 months prior to enrollment
• Age between 15 and 35 years and premenopausal
• Willingness to follow study visit schedule and protocol

• Being pre-menarche or post-menopausal
• Diagnosis of Type 1 or Type 2 Diabetes Mellitus
• Severe kidney problems (creatinine >1.4 mg/dL or eGFR below 45 mL/min/1.73 m2)
• History of lactic acidosis or diabetic ketoacidosis
• Elevated liver enzymes (ALT or AST more than 2.5 times the upper limit of normal)
• Significant mental or chronic systemic illness affecting pain assessment or ability to complete the study
• Current or planned pregnancy or breastfeeding
• Inability to read English or follow study procedures reliably

The trial compares metformin hydrochloride to a placebo over six months. Participants will take metformin starting at 500 mg daily for two weeks, increasing every two weeks to reach 2000 mg daily, or matching placebo tablets with a similar schedule. They will attend clinic visits at the start, 3 months, and 6 months to assess pain and emotional functioning.

Participants will keep daily diaries tracking symptoms like pain, bleeding, and pain medication use. Researchers will measure changes in pain interference, pain severity, emotional health using questionnaires, and overall improvement at each visit. The study monitors safety and evaluates whether metformin affects systemic inflammation and improves quality of life in young women with endometriosis over the 6-month treatment period.