The thyroid gland controls metabolism, energy, and many body functions. Thyroid disorders are among the most common hormonal conditions worldwide — and highly treatable with proper diagnosis and management.
The thyroid gland is a butterfly-shaped gland in the neck that produces thyroid hormones (T3 and T4), which regulate metabolism, heart rate, body temperature, energy levels, and many other essential functions. Thyroid disorders are extremely common, affecting approximately 1 in 10 adults, and are significantly more prevalent in women. Two main categories exist: hypothyroidism (underactive thyroid, too little hormone) and hyperthyroidism (overactive thyroid, too much hormone).
Hypothyroidism — most commonly caused by Hashimoto's thyroiditis (autoimmune destruction of the thyroid) — causes fatigue, weight gain, cold intolerance, hair loss, dry skin, constipation, and depression. It is treated with daily levothyroxine (synthetic thyroid hormone), one of the most commonly prescribed medications in Korea and worldwide. Hyperthyroidism — most commonly caused by Graves' disease (autoimmune overstimulation) — causes weight loss, rapid heart rate, heat intolerance, tremor, and anxiety. Treatment options include antithyroid medications, radioiodine therapy, or surgery.
Thyroid nodules are extremely common — found in up to 50% of adults on ultrasound — and the vast majority are benign, though Korea has notably high rates of thyroid nodule and thyroid cancer detection, partly attributed to widespread use of ultrasound in routine health screening. Thyroid cancer is generally highly curable when detected early. Korea's endocrinology and nuclear medicine services at major hospitals and private clinics offer comprehensive thyroid evaluation including TSH blood tests, thyroid ultrasound, and fine needle aspiration (FNA) biopsy for nodules.
Key Points
- Thyroid disorders affect ~10% of adults — women 5–10x more commonly than men
- TSH blood test is the first-line screening test for thyroid disease
- Hypothyroidism treated with daily levothyroxine — effective and well-tolerated
- Hashimoto's (hypothyroidism) and Graves' disease (hyperthyroidism) are autoimmune
- Korea has notably high rates of thyroid nodule detection due to widespread screening ultrasound use
- Thyroid cancer is generally highly curable when detected early
Causes & Risk Factors
- Hashimoto's thyroiditis — autoimmune destruction causing hypothyroidism
- Graves' disease — autoimmune overstimulation causing hyperthyroidism
- Excess dietary iodine — a notable consideration in Korea given traditional high seaweed (miyeok, dasima) consumption, which can affect thyroid function in susceptible individuals
- Post-thyroidectomy or radioiodine treatment
- Thyroid nodules and multinodular goitre
- Medications including lithium and amiodarone
When to See a Doctor
- Unexplained fatigue, weight gain, hair loss, or feeling cold — request a TSH test
- Unexplained weight loss, rapid heartbeat, tremor, or anxiety
- If you feel a lump or swelling in the neck
- If you are planning pregnancy — thyroid disease can affect fertility and pregnancy
- Annual TSH monitoring if you are on levothyroxine therapy
For emergencies in Korea, call 119
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This content is published for educational purposes only. For accurate diagnosis and personalised treatment, consult a licensed KMA physician in Korea.
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This article is published by DoctorsInKorea.com for educational and informational purposes only. It does not replace a professional clinical evaluation by a licensed healthcare provider. For accurate medical diagnosis and personalised treatment paths, please book an appointment with a licensed KMA physician. For immediate life-threatening medical emergencies in Korea, please call 119.
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Last reviewed: May 29, 2026