Thyrogear 100 mcg Tablet 120's is used for the treatment of hypothyroidism (low secretion of thyroid hormone). It contains Thyroxine, which works by replacing the thyroid hormone in the body when the natural production of thyroid hormones is not sufficient to meet the needs of the body. It usually does not have major side effects when taken regularly in the prescribed dosage but, overdosage may cause headache, nervousness, sleeplessness, irritability, diarrhoea, muscle spasm, weight loss, feeling hot even in cool environments, menstrual irregularities (in women), and skin rash. Before taking this medicine, you should tell your doctor if you are allergic to any of its components or if you are pregnant/breastfeeding, and about all the medications you are taking and pre-existing medical conditions.