Hyperthyroidism — thyrotoxicosis — is the condition of an overactive thyroid gland pouring excessive thyroid hormones (T4 and T3) into the blood, driving the body’s metabolism into overdrive. Sufferers develop a racing heartbeat, trembling hands, sweating, heat intolerance, anxiety, weight loss despite ravenous appetite, and often prominent eyes in Graves’ disease, the commonest cause — an autoimmune attack that stimulates the gland. Diagnosis is blood tests showing suppressed TSH with high thyroid hormones; treatment is antithyroid drugs, radioactive iodine ablation, or surgery. Nutrition matters in management: the hypermetabolic state burns calories and depletes nutrients, and severe untreated disease can precipitate thyroid storm — a life-threatening crisis.