What condition is caused by hyperactivity of the thyroid gland?

Thyrotoxicosis is the condition characterized by an excess of thyroid hormones in the bloodstream, which results from the hyperactivity of the thyroid gland. This can lead to symptoms such as weight loss, rapid heart rate, increased appetite, and anxiety, reflecting the heightened metabolic state that occurs with excessive thyroid hormone levels.

This is distinct from other conditions listed. For instance, thyroxine is a hormone produced by the thyroid gland, not a condition. Hypothyroidism represents a decrease in thyroid hormone production, leading to opposite symptoms such as fatigue and weight gain. Hyperplasia refers to an increase in the number of cells in a tissue or organ, which can occur in various conditions but does not specifically indicate thyroid hormone activity. Thus, thyrotoxicosis clearly identifies the consequence of thyroid gland hyperactivity.