Hydroxychloroquine in Mild Graves' Orbitopathy

Inclusion Criteria: * Mild GO according European Group on Graves' orbitopathy (EUGOGO) guidelines diagnosed by endocrinologist and ophthalmologist. * No previous treatment of GO except for eyedrops * Euthyroidism (normalized free T4 and TSH) for at least 2 months. If radioactive iodine is used for hyperthyroidism, euthyroidism needs to be achieved for at least 6 months. Exclusion Criteria: * Moderate-to-sever or sight-threatening GO according to EUGOGO guidelines diagnosed by endocrinologist and ophthalmologist. * Pregnancy * Drug or alcohol abuse * Unable to comply with the study protocol * Unable to obtain informed consent * Use of hydroxychloroquine or systemic steroid within 3 months prior to enrollment * History of side effects of hydroxychloroquine * History of retinopathy * Renal dysfunction (estimated glomerular filtration rate (eGFR) \< 60ml/min) * Hepatic dysfunction (aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \> 2 x upper limit) * Anemia (hemoglobin (Hb) \< 10g/dl) * Neutropenia (absolute neutrophil count \< 100/uL) * Thrombocytopenia (platelet (PLT) \< 150000/uL) * Glucose-6-phosphate dehydrogenase (G6PD) deficiency * Porphyria cutaneous tarda * Allergy to 4-aminoquinoline