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Underactive thyroid (hypothyroidism): the signs, getting a diagnosis, treatment, and taking the medicine
For anyone just told they have hypothyroidism or Hashimoto’s disease, anyone tired, cold and wondering about their thyroid, anyone starting or changing thyroid medicine, anyone pregnant with a thyroid problem, and anyone caring for someone with one. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK, part of the NIH) says hypothyroidism is when the thyroid gland does not make enough thyroid hormones to meet the body’s needs; that nearly 5 out of 100 Americans ages 12 and older have it; and that it most likely can be completely controlled with thyroid hormone medicine taken as instructed. This page passes on, by name, what NIDDK says: the signs, who gets it and the causes, the blood tests, the medicine and the follow-up tests, and what food, iodine and pregnancy have to do with it. It builds the words to say to a doctor, and prints a card to keep.
A word with a dotted line under it, like this, opens its official definition, quoted from a U.S. government glossary.
Right now
- Someone very hard to wake, newly confused, or passing out, or chest pain: call 911 (ours). NIDDK says myxedema coma, a rare extreme form of untreated hypothyroidism, requires immediate medical treatment.
- A racing or pounding heart, shakiness, or trouble sleeping after a dose change? Call your doctor, and if you cannot reach them, go to urgent care (ours). NIDDK says too much thyroid hormone medicine can cause serious problems.
- Pregnant and taking thyroid medicine? NIDDK says to contact your doctor right away: many women need a higher dose during pregnancy.
- Low mood turning into thoughts of suicide? Call or text 988, any hour (ours).
More help
- Linked to it, on this site: Overactive thyroid (hyperthyroidism) · High cholesterol · Atrial fibrillation · Osteoporosis · Celiac disease · Lupus · Diabetes · Depression.
- The medicine and pregnancy: My medicines list · When medicine costs too much · Pregnancy and a new baby.
- Care and costs: When you need a doctor and can’t pay · Symptom diary · Get ready for your appointment.
- In a crisis: Help right now (988, 911). All our free tools.
Your heart, blood pressure, blood sugar, thyroid or blood, and not sure this is the right page? The pages on this site for a heart attack or stroke, blood pressure, AFib, heart failure, cholesterol, diabetes and prediabetes, the thyroid, anemia, sickle cell and menopause, on one list.
Other guides on this site that go with this page
Free to read. We chose these ourselves; no professional did. Each guide was written with AI and has not been reviewed by a professional. They are general information, not advice.
- Thyroid disease and pregnancy: an overactive or underactive thyroid, the medicines, and after the baby: thyroid disease and pregnancy (an overactive or underactive thyroid while pregnant, Graves’ disease or Hashimoto’s disease, or a thyroid that changed after the baby): why the thyroid matters for the baby, the signs, the medicines used in pregnancy and when to stop and call, a higher dose of thyroid medicine, postpartum thyroiditis, breastfeeding, and iodine.
- Getting ready for thyroid tests: why, the blood tests, the imaging tests, and a nodule: getting ready for thyroid tests (blood tests for TSH, T4, T3 or antibodies, a thyroid ultrasound, a thyroid scan, an uptake test, or a needle biopsy of a nodule): why, the blood tests, the imaging tests, and a nodule.
- Prolactinoma: high prolactin, the signs, the tests, and the treatment: prolactinoma and high prolactin (a benign tumor of the pituitary gland, milk from the breasts, periods that changed or stopped, or less interest in sex): the signs, what else raises prolactin, the tests, the medicines, surgery and radiation, and pregnancy.
- Adrenal insufficiency and Addison’s disease: the signs, adrenal crisis, and staying safe: adrenal insufficiency and Addison’s disease: the signs, adrenal crisis, and staying safe.
- Primary hyperparathyroidism: high calcium, the parathyroid glands, the tests, and surgery or watching: primary hyperparathyroidism, when the parathyroid glands make too much hormone and blood calcium runs high: what it is, who gets it, bones and kidney stones, the signs, the causes, the tests, and surgery, watching, medicines and food.
This page and its wording were written with AI (Claude) for Scarlet Beast (our AI policy). No doctor or nurse has reviewed it. The facts were read on October 16, 2026 on two NIDDK pages (NIH): Hypothyroidism (Underactive Thyroid) (last reviewed March 2021) and Hashimoto’s Disease (last reviewed June 2021). Ours: calling 911 for someone very hard to wake, newly confused, or passing out, or for chest pain; calling the doctor for a racing or pounding heart, shakiness or trouble sleeping after a dose change; 988 for thoughts of suicide; asking the pharmacist about a missed dose or pills that look different, and not doubling up, skipping or changing doses on your own; calling back the same day about a newborn test; the questions to ask at a visit; health centers and medicine costs when money is tight; and the order of the steps. What we left out: brand names, doses, other thyroid medicines, test number ranges, how many times more common Hashimoto’s is in women (NIDDK’s English and Spanish pages give different figures), research studies, and clinical pages for providers. This page saves nothing and loads no trackers.