• Difficulty concentrating
• Fatigue
• Frequent bowel movements
• Goiter (visibly enlarged thyroid gland) or thyroid nodules
• Heat intolerance
• Increased appetite
• Increased sweating
• Irregular menstrual periods in women
• Nervousness
• Restlessness
• Weight loss (rarely, weight gain)

Other symptoms that can occur with this disease:

• Breast development in men
• Clammy skin
• Diarrhea
• Hair loss
• Hand tremor
• Weakness
• High blood pressure
• Itching - overall
• Lack of menstrual periods in women
• Nausea and vomiting
• Pounding, rapid, or irregular pulse
• Protruding eyes (exophthalmos)
• Rapid, forceful, or irregular heartbeat (palpitations)
• Skin blushing or flushing
• Sleeping difficulty

Physical examination may reveal thyroid enlargement, tremor, hyperactive reflexes, or an increased heart rate. Systolic blood pressure (the first number in a blood pressure reading) may be high.

Subclinical hyperthyroidism is a mild form of hyperthyroidism that is diagnosed by abnormal blood levels of thyroid hormones, often in the absence of any symptoms.

Blood tests are also done to measure levels of thyroid hormones.

• TSH (thyroid stimulating hormone) level is usually low
• T3 and free T4 levels are usually high

This disease may also affect the results of the following tests:

• Cholesterol test
• Glucose test
• Radioactive iodine uptake
• T3RU
• Triglycerides
• Vitamin B12 (in rare cases)