Patients with hyperthyroidism experience a significant acceleration of their metabolism. In many cases, this first appears as simple nervousness that many patients attribute to stress. Over time, other symptoms may emerge, including:

• Changes in bowel patterns. In particular, patients are more likely to have increased frequency of bowel movements.
  
  
• Changes to appearance. Patients may experience thinning of the skin and may develop fine, brittle hair.
  
  
• Enlarged thyroid gland. Also known as goiter, this can be felt or even seen as a swelling at the base of the neck.
  
  
• Irregular or rapid heartbeat. Patients may experience irregular heartbeat (arrhythmia) and palpitations. They also may experience rapid heartbeat of more than 100 beats per minute.
  
  
• Irritability. Patients sometimes experience anxiety attacks.
  
  
• Sudden unexplained weight loss. Patients often lose weight despite an appetite and food intake that remain normal or that increases (polyphagia).
  
  
• Sweating. Some patients also may experience increased sensitivity to heat.
  
  
• Tremor. Most often, this appears as a fine trembling in the hands or fingers.
  
  
• Irregular menstruation. Women may experience light or absent periods.

Patients also may experience difficulty sleeping, fatigue and muscle weakness. Symptoms are less likely to be evident in older patients. The use of beta blockers (antihypertensives used to treat high blood pressure and some heart conditions) can mask symptoms of hyperthyroidism.

Patients who experience the swelling behind the eyes known as Graves' ophthalmopathy may have dryness on the surface of the eye. Other symptoms include red or swollen eyes, excessive tearing or discomfort in the eyes, and any of the following:

• Blurry or double vision
  
• Inflammation
  
• Sensitivity to light
  
• Reduced eye movement