Graves' disease. Graves' disease is the most common cause of overactive thyroid. It can run in families and can occur at any age, although it is most common in women aged 20-40 years old. You are more likely to develop Graves' disease if you smoke. Graves' disease is an autoimmune condition.
Full Removal. If your doctor removes your entire thyroid, your body will begin to exhibit symptoms similar to hypothyroidism, due to the lack of thyroid hormones in your body. These symptoms may include fatigue, elevated cholesterol levels, uncontrollable weight gain, muscle weakness and depression.
TSH is the main hormone tested by your doctor to determine if your thyroid gland is functioning properly. Too much TSH means the pituitary gland is trying to get a sluggish thyroid gland to work better. Too little means there is enough thyroxin in your body so TSH remains low until more is needed.