A condition in which the thyroid gland does not produce enough thyroid hormone.


  • General: letheragy, fatigue, weight gain and cold intolerance
  • Skin: dry skin, brittle nails and thinning hair
  • Eyes: puffy eyes
  • Cardiovascular system: slowing of heart rate, high blood pressure
  • Respiratory system: shortness of breath on exertion, sleep apnea, hoarseness of the voice
  • Digestive system: constipation
  • Neuromuscular system: muscle aches and pains, depression, mental slowing, neuromuscular slowing, weakness
  • Reproductive system: irregular menstrual cycles, infertility, increased risk of miscarriage, leakage of milk from the breast


History and physical examination are supplemented with blood tests.

TSH (Thyroid Stimulating Hormone): TSH is the pituitary hormone which turns on the thyroid gland and causes thyroid hormone to be produced. When thyroid hormone levels are low, TSH is high. High TSH is the hallmark of hypothyroidism.

Free T4: Free T4 levels are low or in the lower part of the normal range, depending on the severity of the hypothyroidism.

Anti-Thyroid Antibodies (Anti-TPO and Anti-Thyroglobulin Antibodies): A large percentage of patients with autoimmune thyroid disease will have elevated anti-thyroid antibodies. Antibodies usually indicate the immune system is attacking the thyroid gland. The absence of these antibodies does not exclude the diagnosis of hypothyroidism, nor does the presence of these antibodies indicate that thyroid hormone replacement therapy is needed.

Causes of Hypothyroidism:

Hashimoto’s Thyroiditis is the cause of hypothyroidism in 95% of cases. It is part of the larger spectrum of illnesses called autoimmune thyroid disease (Graves Disease, Lymphocytic Thyroiditis, Nodular Thyroid Disease) in which the immune system forms antibodies against thyroid tissues that result in failure of the gland. It is often associated with enlargement of the thyroid gland (goiter). The gland is usually hard and rubbery.

Medications: Some medications can result in hypothyroidism including amiodarone, iodine, radioactive iodine or thionamides (methimazole and PTU).

Surgical Hypothyroidism: removal of the thyroid gland.

Pituitary Disease: Failure of the thyroid to produce TSH.


Thyroid hormone can be produced synthetically and is readily available as an oral medication. The overwhelming majority of thyroid specialists prefer to treat hypothyroidism with oral levothyroxine therapy (Synthroid, Levoxyl, levothyroxine) or T4. Medication is taken once daily on an empty stomach to optimize absorption. Care should be taken to avoid taking the medication with iron, calcium, fiber of aluminum which can decrease its absorption.

In very rare cases, patients may be treated with (triiodothyroine) T3 or combinations of T4 and T3. Studies comparing the effectiveness of T4 therapy to T4 and T3 combination therapy show that T4 therapy alone is as effective as combination therapy. Since the latter is more costly and more difficult to work with, T4 therapy is preferred.

Monitoring Therapy:

After a change is made in thyroid hormone dose, it takes several weeks to a month for the patient to feel better and 5–6 weeks for the thyroid hormone levels to stabilize in the blood.

Dose adjustments must be made very cautiously in the elderly or those with a history of heart disease. Thyroid hormone requirement will increase in about 70% of pregnant women and must be followed very closely over the course of pregnancy. Proper thyroid hormone replacement will result in mothers delivering normal children.