- In adulthood, hyperthyroidism causes hyperexcitability and irritability.
- For the autonomic nervous system, thyroid hormone (T3 and T4) has many of the same actions as the sympathetic nervous system because it up-regulates beta-1-adrenergic receptors in the heart.  Therefore, a useful adjunct therapy for hyperthyroidism is treatment with beta-adrenergic blocking agents, such as propranolol.
- Symptoms of hyperthyroidism include increased metabolic rate, weight loss, negative nitrogen balance, increased heat production (sweating), increased cardiac output (by increasing heart rate and stroke volume), dyspnea (shortness of breath - hence increased ventilation), tremor, weakness, exophtlamos, and goiter.
- Causes of hyperthyroidism include Grave's Disease and thyroid neoplasm.
- Hyperthyroidism also causes decreased TSH levels because of feedback inhibition on the anterior pituitary gland by high thyroid hormone levels.)
- Treatment of hyperthyroidism include propylthiouracil (which inhibits thyroid hormone synthesis by blocking the peroxidase enzyme that converts I- to I2. 
- Thyroidectomy is also a treatment (removal of the thyroid gland).
- Radioactive iodine isotope administration is another treatment method which destroys the thyroid.
- beta-blockers are another treatment therapy.