Efficacy of Subantimicrobial Dose Doxycycline for Moderate to Severe and Active Graves' Orbitopathy

Inclusion Criteria: * Clinical diagnosis of Graves' Orbitopathy * Moderate-severe GO According to EUGOGO statements, patients with moderate-severe GO usually have any one or more of the following：moderate or severe soft tissue involvement, exophthalmos≥3mm above normal for race and gender, inconstant, or constant diplopia. * Clinical activity score ≥ 3 * Being euthyroid for at least 1 month before the date of inclusion * Must be able to swallow tablets * Written informed consent is obtained Exclusion Criteria: * Mild Graves' Orbitopathy * Sight-threatening Graves' Orbitopathy * Clinical activity score \< 3 * Previous treatment for GO Oral steroids, intravenous steroids, radiotherapy * Pregnant females as determined by positive (serum or urine) Human chorionic gonadotropin (hCG) test at screening or prior to dosing, or lactating females * Uncontrolled diabetes or hypertension * History of mental / psychiatric disorder * Hepatic dysfunction (Albumin (Alb),Aspartate Transaminase (AST), Alanine Aminotransferase (ALT) and Alkaline phosphates levels must be within normal range for eligibility) * Renal impairment (Urea and Creatinine levels must be within normal range) * Doxycycline allergy or intolerance