Hypothyroidism vs. hyperthyroidism: What’s the difference? | NIH MedlinePlus Magazine

Hypothyroidism (or underactive thyroid)

  • When your thyroid gland doesn’t make enough thyroid hormone
  • May cause weight gain, constipation, slowed heart rate, dry skin and hair, sensitivity to cold

Hyperthyroidism (or overactive thyroid)

  • When your thyroid gland makes too much thyroid hormone
  • May cause weight loss, nervousness, frequent bowel movements, sensitivity to cold, and muscle weakness

Both

  • More likely to affect women
  • Symptoms like fatigue and an enlarged thyroid, also called a goiter, which may make your neck look swollen
  • Can be caused by autoimmune diseases, which cause your body to attack itself

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