The essentials

Hashimoto's thyroiditis is an autoimmune disease in which the immune system slowly damages the thyroid. It is the most common cause of an underactive thyroid in the United States and is 4 to 10 times more common in women. Diagnosis rests on TSH, FT4 and thyroid antibodies. Some people only need regular blood tests; those who develop hypothyroidism take a daily hormone tablet. Call 911 for confusion, extreme drowsiness or trouble breathing.

What is Hashimoto's thyroiditis, at a glance?

Hashimoto's thyroiditis, also called Hashimoto's disease, chronic lymphocytic thyroiditis or autoimmune thyroiditis, is an autoimmune disorder of the thyroid gland[2]. White blood cells and antibodies attack the gland, which can lose its ability to make enough hormone[1]. It is the most common cause of hypothyroidism (underactive thyroid), a condition that affects about 5 in 100 Americans[1]. The exact number of people with Hashimoto's is unknown, but thyroid antibodies are common: a national US survey found TPO antibodies in about 11% of people aged 12 and over[7].

  • Who: mostly women, often between ages 30 and 50, but teens, men and older adults can have it too[1].
  • Key blood tests: TSH, FT4 and thyroid antibodies (TPO and thyroglobulin antibodies)[1][4].
  • Treatment: none while the thyroid works normally; levothyroxine once hypothyroidism develops[2].

What are the symptoms of Hashimoto's thyroiditis?

Many people have no symptoms at first[1]. The first sign can be a goiter: a painless swelling at the front of the neck[1].

When hormone levels fall, the symptoms are those of hypothyroidism and appear gradually[1]:

  • Common Tiredness, weight gain and feeling cold when others are not[1].
  • Common Dry skin, dry or thinning hair, and constipation[1].
  • Common Joint and muscle aches[1].
  • Possible Heavy or irregular periods, or trouble getting pregnant[1].
  • Possible A slower heart rate[1].
  • Rare A short overactive phase early on (hashitoxicosis), with palpitations or weight loss[1].

These symptoms have many other causes, so blood tests confirm the diagnosis.

When should I see a doctor?

When to see a doctor

  • Emergency: call 911 for confusion, extreme drowsiness, a very low body temperature, slow or difficult breathing, or fainting in someone with known or suspected hypothyroidism. Untreated hypothyroidism can rarely lead to myxedema, a life-threatening slowing of body functions[1].
  • Within 24 to 48 hours if you take levothyroxine and have a racing or irregular heartbeat, chest discomfort or shaking, which can mean the dose is too high[1], or if you have just learned you are pregnant and have Hashimoto's[11].
  • At your next appointment for lasting tiredness, weight gain, feeling cold, dry skin, a painless swelling in the neck, or a TSH flagged H on a routine test.

What causes Hashimoto's thyroiditis, and who is at risk?

The cause is unknown. It most likely results from genes combined with environmental and epigenetic factors[1][9].

How is Hashimoto's thyroiditis diagnosed, and how do I read the results?

Your doctor takes your history, examines your neck for a goiter and orders blood tests[1]. The diagnosis is based on a high TSH, with or without a low FT4, and/or a goiter, with positive thyroid antibodies when they are measured[2]. Most people with Hashimoto's have high levels of TPO antibodies, thyroglobulin antibodies or both[4]. Imaging and biopsy are generally not needed[3]; an ultrasound may be used when Hashimoto's is suspected but antibodies are absent, or to check for nodules[1]. Here is a fictitious report with a typical early pattern.

Fictitious example of a lab report line (United States format)
TestResultReference rangeFlag
TSH7.8 mIU/L0.4-4.8 mIU/LH
FT4 (unbound thyroxine)1.0 ng/dL0.8-1.9 ng/dL
Thyroid peroxidase antibodies (TPO Ab)210 IU/mLLess than 35 IU/mLH
Thyroglobulin antibodies (TgAb)12 IU/mLLess than 40 IU/mL
  1. TSH: the pituitary's signal to the thyroid. It rises when the gland starts to struggle, often before FT4 falls[5].
  2. FT4: the unbound, active form of the main thyroid hormone, still in range here. A high TSH with a normal FT4 is called subclinical (mild) hypothyroidism; a high TSH with a low FT4 is overt hypothyroidism[2][6].
  3. TPO and thyroglobulin antibodies: a positive result points to an autoimmune cause such as Hashimoto's[4]. One positive antibody is enough. Antibody reference limits differ widely between methods and laboratories.

Got a thyroid report with an H next to TSH or your antibodies? BloodSense explains each line of your full report and helps you prepare questions for your next visit.

Get my thyroid results explained

Typical adult ranges are 0.4 to 4.8 mIU/L for TSH and 0.8 to 1.9 ng/dL for FT4; some labs use a higher upper TSH limit for older people[5][6]. Positive antibodies with a normal TSH mean autoimmunity without thyroid failure. In a 20-year follow-up of a large community survey, women with both a raised TSH and positive antibodies had a much higher risk of later hypothyroidism than women with neither[8].

Each test has its own guide: the thyroid panel explained, the TSH blood test, the FT4 blood test, FT3 results, what a high anti-TPO result means, and the TPO antibody lab test in our dictionary.

How is Hashimoto's thyroiditis monitored?

Monitoring depends on how well your thyroid works:

  • Antibodies with normal thyroid function: no treatment is needed; your doctor follows your symptoms and hormone levels over time[1][2].
  • Once on levothyroxine: a first blood test about 6 to 8 weeks after starting, and again after each dose change; once the dose is right, tests are repeated in 6 months, then once a year[1]. Many people have TSH checked once or twice a year[2].
  • Antibodies: repeating and monitoring antibody levels is not needed; treatment is guided by TSH, not by the antibody number[2].
  • Pregnancy: thyroid tests are checked as soon as pregnancy is known, and the levothyroxine dose often needs adjusting, with TSH measured regularly during the first half of pregnancy[4][11].

How is Hashimoto's thyroiditis treated?

Treatment replaces the hormone the thyroid can no longer make; nothing stops the autoimmune attack itself. No doses are given here: your doctor adjusts them to your TSH[2].

  • Levothyroxine is identical to the T4 your thyroid makes and is the recommended treatment for hypothyroidism[1][10]. It is taken by mouth once a day, on an empty stomach, 30 to 60 minutes before breakfast[1].
  • Mild (subclinical) hypothyroidism may or may not need medicine right away; the decision depends on your TSH, symptoms, age and plans for pregnancy[2].
  • The right dose matters: too much levothyroxine can cause atrial fibrillation or bone thinning (osteoporosis), which is why blood tests continue[1]. Some medicines and supplements, such as calcium or iron, can reduce its absorption, so tell your doctor and pharmacist what you take[10].
  • A new lump should be checked: very rarely, a thyroid lymphoma or thyroid cancer can develop in Hashimoto's thyroiditis[3][9].

Most people with overt hypothyroidism from Hashimoto's need lifelong thyroid hormone replacement[2]. Untreated, hypothyroidism can raise cholesterol and contribute to heart disease and heart failure[1]; see our pages on high cholesterol and heart failure.

Can diet or selenium help, and how do I live with Hashimoto's?

A few habits help:

  • Take levothyroxine at the same time every day, as advised, and do not stop it on your own[1].
  • Limit high-iodine foods such as kelp, dulse and other seaweed, iodine supplements and iodine-rich medicines like some cough syrups; ask your care team what to limit[1].
  • Do not start iodine or selenium supplements without advice. Selenium and vitamin D are being studied, and no specific guidance is currently available[1].
  • Tell your doctor before trying to get pregnant: untreated hypothyroidism can cause problems in pregnancy[1].

On selenium, a 2024 meta-analysis of 35 randomized trials found that supplements lowered TPO antibodies and, in people not taking thyroid hormone, lowered TSH slightly, with no change in FT4[12]. It does not replace levothyroxine; discuss it with your doctor. The selenium blood test page explains how selenium status is measured.

Questions to ask your doctor

  1. Do my TSH, FT4 and antibody results fit Hashimoto's thyroiditis?
  2. Is my thyroid working normally for now, or do I have hypothyroidism?
  3. Do I need treatment now, or only regular blood tests?
  4. How often should my TSH be checked, and should I take my tablet before the test?
  5. What should I do if I plan a pregnancy?

Frequently asked questions

Is Hashimoto's the same as hypothyroidism?

No. Hypothyroidism is the state of having too little thyroid hormone. Hashimoto's is a disease that often, but not always, leads to it. Some people have Hashimoto's antibodies for years with a normal thyroid[2].

Are there stages of Hashimoto's?

There is no single official staging. Doctors describe where you are by thyroid function: antibodies with normal function, mild (subclinical) hypothyroidism, then overt hypothyroidism. Treatment needs differ at each step[2].

Can Hashimoto's cause an overactive thyroid?

Rarely, early in the disease, the inflamed gland releases stored hormone and causes temporary hyperthyroidism[1]. Lasting overactivity usually has another cause, such as Graves' disease, the other main autoimmune thyroid disease.

Do I need to avoid gluten?

Not for Hashimoto's alone: there is no specific diet for it[1]. Hashimoto's is more common in people with celiac disease, though, and celiac disease does require a strict diet without gluten[1].

  1. National Institute of Diabetes and Digestive and Kidney Diseases. Hashimoto's Disease. National Institutes of Health. niddk.nih.gov (accessed October 28, 2026)
  2. American Thyroid Association. Hashimoto's Thyroiditis. thyroid.org (accessed October 28, 2026)
  3. MedlinePlus Medical Encyclopedia. Chronic thyroiditis (Hashimoto disease). US National Library of Medicine. medlineplus.gov (accessed October 28, 2026)
  4. MedlinePlus. Thyroid Antibody Tests. US National Library of Medicine. medlineplus.gov (accessed October 28, 2026)
  5. MedlinePlus Medical Encyclopedia. TSH test. US National Library of Medicine. medlineplus.gov (accessed October 28, 2026)
  6. MedlinePlus Medical Encyclopedia. FT4 test. US National Library of Medicine. medlineplus.gov (accessed October 28, 2026)
  7. Hollowell JG, Staehling NW, Flanders WD, et al. Serum TSH, T4, and thyroid antibodies in the United States population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III). J Clin Endocrinol Metab. 2002;87(2):489-499. doi:10.1210/jcem.87.2.8182 (accessed October 28, 2026)
  8. Vanderpump MP, Tunbridge WM, French JM, et al. The incidence of thyroid disorders in the community: a twenty-year follow-up of the Whickham Survey. Clin Endocrinol (Oxf). 1995;43(1):55-68. doi:10.1111/j.1365-2265.1995.tb01894.x (accessed October 28, 2026)
  9. Ralli M, Angeletti D, Fiore M, et al. Hashimoto's thyroiditis: an update on pathogenic mechanisms, diagnostic protocols, therapeutic strategies, and potential malignant transformation. Autoimmun Rev. 2020;19(10):102649. doi:10.1016/j.autrev.2020.102649 (accessed October 28, 2026)
  10. Jonklaas J, Bianco AC, Bauer AJ, et al. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement. Thyroid. 2014;24(12):1670-1751. doi:10.1089/thy.2014.0028 (accessed October 28, 2026)
  11. Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartum. Thyroid. 2017;27(3):315-389. doi:10.1089/thy.2016.0457 (accessed October 28, 2026)
  12. Huwiler VV, Maissen-Abgottspon S, Stanga Z, et al. Selenium supplementation in patients with Hashimoto thyroiditis: a systematic review and meta-analysis of randomized clinical trials. Thyroid. 2024;34(3):295-313. doi:10.1089/thy.2023.0556 (accessed October 28, 2026)

This page is general information. It does not replace the advice of a doctor, who interprets your results with your symptoms, history and examination.