Hyperthyroidism is the clinical term for an overactive thyroid gland. Patients with hyperthyroidism produce excessive quantities of the thyroid hormones thyroxine and triiodothyronine, which speed up the metabolic processes and functions of the body. Symptoms of hyperthyroidism include sudden weight loss without dieting, rapid and racing heartbeat, nervousness, irritability, tremors, increased perspiration, more frequent bowel movements, and changes in menstrual patterns.