Underactive thyroid (hypothyroidism)

For a lay person:

Hypothyroidism means the thyroid gland does not make enough thyroid hormone, so the body's processes slow down. It is more common in women and older adults and causes tiredness, weight gain, feeling cold, constipation and low mood, often coming on slowly.

For a trained medical person:

Most commonly due to autoimmune (Hashimoto's) thyroiditis in iodine-sufficient regions, with other causes including iodine deficiency, thyroidectomy, radioiodine treatment, drugs such as amiodarone and lithium, and pituitary disease. Diagnosis is by raised TSH with low free T4, with thyroid peroxidase antibodies supporting autoimmune disease. Treatment is levothyroxine replacement titrated to TSH.

In Chinese medicine:

Liu and Tseng's textbook gives Chinese herbal formulas for this condition without a full pattern differentiation. Treatment still follows the pattern a patient presents with, not the Western diagnosis alone.

When to get help: Seek urgent care for drowsiness, confusion, very low body temperature or a slow heart rate, which can signal myxoedema coma. Do not stop thyroid medication for herbs, and avoid high-iodine seaweed or kelp products unless your doctor agrees.