Hyperthyroidism is a condition caused by an overactive thyroid gland. The gland makes too much T4 and T3 hormones. Hormones are substances that affect and control many important functions in the body.

The thyroid gland is located in the neck. It produces several hormones which control the way that every cell in the body uses energy (metabolism). The thyroid is part of the endocrine system.

Hyperthyroidism or thyrotoxicosis occurs when the thyroid releases too many of its hormones over a short (acute) or long (chronic) period of time. Many diseases and conditions can cause this problem, including:

• Graves disease
• Non-cancerous growths of the thyroid gland or pituitary gland
• Tumors of the testes or ovaries
• Inflammation (irritation and swelling) of the thyroid due to viral infections or other causes
• Ingestion (taking in through the mouth, such as in eating) of large amounts of thyroid hormone
• Ingestion of excessive iodine

Graves disease accounts for 85% of all cases of hyperthyroidism.

Related topics:

• Painless (silent) thyroiditis
• Factitious hyperthyroidism
• Hypothyroidism
• Graves disease

• Weight loss
• Increased appetite
• Nervousness
• Restlessness
• Heat intolerance
• Increased sweating
• Fatigue
• Frequent bowel movements
• Menstrual irregularities in women
• Goiter (visibly enlarged thyroid) may be present

• Weakness
• Sleeping difficulty
• Clammy skin
• Skin blushing or flushing
• Bounding pulse
• Nausea and vomiting
• Lack of menstruation
• Itching - overall
• Heartbeat sensations
• Hand tremor
• Hair loss
• Diarrhea
• Breast development in men
• High blood pressure
• Protruding eyes (exophthalmos)

Physical examination may reveal thyroid enlargement or goiter. Vital signs (temperature, pulse, rate of breathing, blood pressure) show increased heart rate. Systolic blood pressure (the first number in a blood pressure reading) may be high.

Laboratory tests that evaluate thyroid function:

• Serum TSH is usually low
• T3 and free T4 are usually high

• Vitamin B-12
• TSI
• Triglycerides
• RT3U
• Radioactive iodine uptake
• Glucose test
• Cholesterol test
• Antithyroglobulin antibody