Levothyroxine (T4) is a synthetic form of the thyroid hormone thyroxine, widely prescribed to restore and maintain normal metabolic balance in individuals with thyroid hormone deficiency. It plays a crucial role in regulating energy production, growth, and overall metabolic activity by mimicking the natural hormone secreted by the thyroid gland. Levothyroxine is primarily used in the management of hypothyroidism, where it helps alleviate symptoms such as fatigue, weight changes, and slowed bodily functions by replenishing hormone levels. It is also essential in cases of goiter, where stabilizing thyroid function can reduce gland enlargement. Beyond these, Levothyroxine is prescribed as a lifelong replacement therapy for patients who have undergone thyroid surgery or radioiodine treatment, ensuring the body continues to function normally without the natural gland. In certain thyroid cancers, it is used to suppress thyroid-stimulating hormone (TSH), thereby reducing the risk of tumor growth. By supporting heart health, brain development, and metabolic stability, Levothyroxine remains a cornerstone therapy in endocrine care.