Hypothyroidism is an underactive thyroid: the gland produces too little thyroid hormone, and metabolism slows throughout the body. It is common, particularly in women and with age, and it is straightforward to treat once identified.
Causes
Hypothyroidism can result from various factors, often leading to insufficient thyroid hormone production:- Hashimoto's Thyroiditis: This is the most common cause of hypothyroidism. It's an autoimmune disorder where the immune system mistakenly attacks and gradually destroys the thyroid gland.
- Thyroiditis: Inflammation of the thyroid gland can temporarily cause hypothyroidism. This includes subacute thyroiditis (often after a viral infection), postpartum thyroiditis (after childbirth), or silent thyroiditis.
- Treatment for Hyperthyroidism: Individuals who have been treated for an overactive thyroid (hyperthyroidism) with radioactive iodine therapy or surgical removal of the thyroid gland (thyroidectomy) often develop permanent hypothyroidism.
- Iodine Deficiency: Iodine is essential for thyroid hormone production. While less common in regions with iodized salt, a severe lack of dietary iodine can lead to hypothyroidism.
- Certain Medications: Some drugs can interfere with thyroid hormone production or function, including:
- Lithium (used for bipolar disorder)
- Amiodarone (a heart medication)
- Interferon alpha
- Some cancer medications
- Congenital Hypothyroidism: Some babies are born with an underdeveloped or absent thyroid gland.
- Pituitary Disorder: Rarely, a problem with the pituitary gland (which produces TSH, thyroid-stimulating hormone) can lead to the thyroid not being stimulated enough to produce hormones.
- Radiation Therapy: Radiation to the neck or head for other cancers can damage the thyroid gland.
Symptoms
The symptoms of hypothyroidism often develop slowly over time and can be subtle, making them easy to overlook or attribute to aging. They are generally related to a slowed metabolism:- Fatigue and sluggishness: Feeling tired and lacking energy, even after adequate sleep.
- Weight gain: Despite no changes in diet or activity levels.
- Increased sensitivity to cold: Feeling cold even in warm environments.
- Constipation.
- Dry skin and brittle nails.
- Thinning hair or hair loss.
- Muscle aches, tenderness, and stiffness.
- Joint pain and swelling.
- Depression.
- Impaired memory and concentration ("brain fog").
- Slowed heart rate (bradycardia).
- Heavy or irregular menstrual periods in women.
- Hoarseness.
- Enlarged thyroid gland (goiter): A swelling at the base of the neck, though not always present.
Diagnosis
Hypothyroidism is diagnosed through a physical examination, review of symptoms, and blood tests to measure thyroid hormone levels.- Medical History and Physical Exam: The doctor will ask about your symptoms, family history, and conduct a physical exam, checking your pulse, examining your neck for an enlarged thyroid, and looking for dry skin or other signs.
- Blood Tests:
- Thyroid-Stimulating Hormone (TSH): This is the most important test. In hypothyroidism, TSH levels are typically elevated (because the pituitary gland produces more TSH in an attempt to stimulate the underactive thyroid).
- Thyroxine (T4): Levels of this thyroid hormone will be low in hypothyroidism.
- Thyroid peroxidase (TPO) antibodies: These antibody tests can help diagnose Hashimoto's thyroiditis.
- Thyroid Ultrasound: May be used to visualize the thyroid gland and identify any nodules or structural abnormalities, though not typically for routine diagnosis of hypothyroidism.
Treatment
Hypothyroidism is a lifelong condition that is managed by replacing the missing thyroid hormone.- Thyroid Hormone Replacement Medication:
- Levothyroxine (Synthroid, Levoxyl, etc.): This synthetic form of thyroxine (T4) is the standard treatment. It is taken orally, usually once daily on an empty stomach.
- The dosage is carefully adjusted based on TSH levels to restore them to a normal range. It can take several weeks for symptoms to improve after starting medication or adjusting the dose.
- Regular Monitoring:
- Blood tests (TSH levels) are regularly performed to ensure the medication dosage is correct.
- Follow-up appointments with your doctor are essential to monitor symptoms and adjust treatment as needed.
- Dietary Considerations:
- Avoid taking levothyroxine with calcium, iron supplements, or certain foods (e.g., soy products, high-fiber foods) as they can interfere with absorption. It's best to take it at least 30-60 minutes before breakfast.
- While iodine deficiency is a cause, excessive iodine intake from supplements should be avoided, as it can sometimes worsen autoimmune thyroid conditions.
Getting Levothyroxine Right
Hypothyroidism is among the most straightforward chronic conditions to treat, and among the most common to treat badly, because levothyroxine is unusually sensitive to how and when it is taken. Most persistent problems trace back to one of a handful of details.
Taking it so it is absorbed
Levothyroxine is absorbed reliably only on an empty stomach, 30 to 60 minutes before breakfast or at bedtime at least three hours after the last meal. Calcium, iron, antacids, and soy taken within four hours cut absorption sharply, as does coffee taken with the tablet. Switching between manufacturers changes the delivered dose slightly, so staying on the same product and rechecking levels after any change avoids drift.
Dose changes and when to recheck
TSH is rechecked six to eight weeks after any dose change, not sooner, because the level takes that long to settle. The goal is a TSH in the normal range, and pushing it below normal in the hope of more energy is harmful: over-replacement raises the risk of atrial fibrillation and bone loss, particularly in older adults. Pregnancy raises the requirement by about a third from the first weeks, so anyone planning a pregnancy should have a plan agreed in advance.
Symptoms that persist with a normal TSH
A proportion of people feel unwell despite a TSH in range, and the reflex to raise the dose is usually wrong. Sleep apnea, B12 deficiency, anemia, depression, and vitamin D deficiency all cause the same fatigue and are worth ruling out. A trial of combined T4 and T3 treatment is reasonable in selected people who remain symptomatic, while desiccated thyroid extract is not recommended routinely because its hormone content varies. Our when to get your thyroid checked article covers the broader evaluation.
Mildly high TSH does not always mean treatment
A TSH slightly above range with a normal T4 is subclinical hypothyroidism, and up to half of such results normalize on repeat testing within a few months, so the test is repeated before anything is prescribed. Treatment is generally advised when TSH is above 10, when thyroid antibodies confirm Hashimoto's thyroiditis, or when pregnancy is planned. Levothyroxine started for a borderline result often ends up as a lifelong prescription that was never needed.
Weight, and what the medication does not do
Untreated hypothyroidism adds a modest amount of weight, mostly fluid, and correcting it removes that amount and no more. Levothyroxine is not a weight-loss treatment, and using it as one carries the cardiac and bone risks above. Our endocrine team manages difficult cases. The American Thyroid Association and NIDDK publish patient guidance on treatment and monitoring.
If you still feel unwell on levothyroxine, or have not had a TSH check in the past year, schedule a visit.