Hypothyroidism is a clinical condition characterised by insufficient thyroid hormone production, leading to a reduced metabolic rate and impaired physiological functions. It matters in clinical practice because untreated hypothyroidism can cause significant symptoms such as fatigue, weight gain, and cognitive impairment, and may progress to life-threatening myxoedema. A key complication is the development of cardiovascular disease due to altered lipid metabolism and increased atherosclerosis risk.