Thyroid hormones are thyroxine (T4) and triiodothyronine (T3), which regulate metabolism, thermoregulation, growth and development, and also affect the cardiovascular and nervous systems.
Disorders in their production lead to hypothyroidism (deficiency) or hyperthyroidism (excess), which can affect energy levels, body weight, pulse rate, cold/heat tolerance and emotional state. To assess thyroid function, TSH levels and clinical manifestations are usually also taken into account.