Two common thyroid conditions include hypothyroidism and hyperthyroidism. Hypothyroidism is when a person has an underactive thyroid. This occurs when the thyroid gland does not produce enough of certain hormones. Hyperthyroidism is when a person has an overactive thyroid. This is a condition that occurs when the thyroid gland produces too much of the hormone thyroxine. There are a number of signs and symptoms that may be associated with either of these conditions.