Which condition is characterized by decreased activity of the thyroid gland?

Hypothyroidism is characterized by decreased activity of the thyroid gland, leading to insufficient production of thyroid hormones such as thyroxine (T4) and triiodothyronine (T3). This condition results in a range of symptoms including fatigue, weight gain, cold intolerance, and depression due to the overall reduction in metabolic processes regulated by these hormones. The thyroid gland plays a crucial role in regulating metabolism, and when it is underactive, the body's systems slow down, leading to the clinical manifestations associated with hypothyroidism.

In contrast, hyperthyroidism refers to an overactive thyroid gland producing excess hormones, which accelerates metabolism and can cause symptoms such as weight loss, heat intolerance, and anxiety. Graves' disease is a specific autoimmune condition that is one of the most common causes of hyperthyroidism. Cushing's syndrome results from excess cortisol production and is not related to thyroid function at all. Hence, the distinction between these conditions underscores why hypothyroidism is properly identified as the condition with decreased thyroid gland activity.