Hypothyroidism: Symptoms, Causes & Treatment Guide
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
At a Glance
TL;DR: Hypothyroidism — also called underactive thyroid — happens when the thyroid gland doesn't make enough thyroid hormone. Symptoms develop slowly over years and often start with fatigue and weight gain that feel like "just getting older." The condition is diagnosed with blood tests, not symptoms alone. Treatment is usually a daily thyroid hormone pill (levothyroxine) that most people take for life, and you'll likely feel better within one to two weeks of starting. Take it on an empty stomach, never stop because you feel better, and expect regular TSH blood tests to fine-tune the dose.
Quick Answer:
What is hypothyroidism? A condition in which the thyroid gland — a small, butterfly-shaped gland at the base of the neck — doesn't make enough of the hormones T-4 and T-3, which affect every cell in the body.
What are the main symptoms? Tiredness, cold sensitivity, constipation, dry skin, weight gain, puffy face, hoarse voice, coarse or thinning hair, muscle weakness and aches, heavier or irregular periods, slowed heart rate, depression, and memory problems.
How is it diagnosed? With blood tests: a high thyroid-stimulating hormone (TSH) level plus a low T-4 level confirms hypothyroidism. If T-4 and T-3 are normal despite high TSH, it's called subclinical hypothyroidism.
What causes it? Most often an autoimmune disease called Hashimoto's disease. Other causes include thyroid surgery, radiation therapy, thyroiditis, and certain medicines such as lithium.
How is it treated? Usually with the daily oral hormone medicine levothyroxine. Treatment is typically lifelong, and you'll likely feel better one to two weeks after starting.
How do you take it correctly? On an empty stomach, ideally in the morning with water, waiting 30–60 minutes before eating. Don't skip doses or stop when you feel better.
Is it dangerous if ignored? Untreated hypothyroidism can raise cholesterol and heart risk, cause nerve damage and infertility — and rarely, a life-threatening emergency called myxedema coma.
What Is Hypothyroidism?
Hypothyroidism happens when the thyroid gland doesn't make enough thyroid hormone. This condition also is called underactive thyroid.
The thyroid is a small, butterfly-shaped gland located at the base of the neck, just below the Adam's apple. It makes two main hormones: thyroxine (T-4) and triiodothyronine (T-3). These hormones affect every cell in the body. They support the rate at which the body uses fats and carbohydrates, help control body temperature, affect heart rate, and help control how much protein the body makes.
Here's the catch: hypothyroidism may not cause noticeable symptoms in its early stages. Over time, hypothyroidism that isn't treated can lead to other health concerns, such as high cholesterol and heart conditions.
The encouraging part: blood tests are used to diagnose hypothyroidism, and treatment with thyroid hormone medicine usually is simple, safe and effective once you and your healthcare professional find the right dosage for you.
What Are the Symptoms of Hypothyroidism?
The symptoms of hypothyroidism depend on the severity of the condition. Symptoms tend to develop slowly, often over several years.
At first, you may barely notice the symptoms of hypothyroidism, such as fatigue and weight gain. Or you may think they are just part of getting older. But as your metabolism continues to slow, you may develop more-obvious problems.
Hypothyroidism symptoms may include:
Tiredness.
More sensitivity to cold.
Constipation.
Dry skin.
Weight gain.
Puffy face.
Hoarse voice.
Coarse hair and skin.
Muscle weakness.
Muscle aches, tenderness and stiffness.
Menstrual cycles that are heavier than usual or irregular.
Thinning hair.
Slowed heart rate, also called bradycardia.
Depression.
Memory problems.
Symptom | What You Might Notice | Why It Happens |
Tiredness | Low energy even after rest | Slowed metabolism affects every cell |
Cold sensitivity | Feeling chilled when others are fine | T-4 and T-3 help control body temperature |
Weight gain | Gradual, hard-to-explain increase | Slower use of fats and carbohydrates |
Dry, coarse skin and thinning hair | Rough skin, hair loss or coarse texture | Hormones affect cell turnover |
Constipation | Slower digestion | Metabolism, including the digestive tract, slows |
Puffy face, hoarse voice | Facial swelling, voice changes | Fluid and tissue changes from low hormone levels |
Muscle weakness, aches, stiffness | Aching muscles, reduced strength | Muscles affected by low hormone activity |
Heavier or irregular periods | Menstrual changes | Hormone balance is disrupted |
Slowed heart rate (bradycardia) | Slow pulse | Thyroid hormones affect heart rate |
Depression, memory problems | Low mood, foggy thinking | Brain function is affected |
How Does Hypothyroidism Look in Infants?
Anyone can get hypothyroidism, including infants. Most babies born without a thyroid gland or with a gland that doesn't work correctly don't have symptoms right away. But if hypothyroidism isn't diagnosed and treated, symptoms start to appear. They may include feeding problems, poor growth, poor weight gain, yellowing of the skin and the whites of the eyes (a condition called jaundice), constipation, poor muscle tone, dry skin, hoarse crying, an enlarged tongue, and a soft swelling or bulge near the belly button called an umbilical hernia.
When hypothyroidism in infants isn't treated, even mild cases can lead to severe physical and mental development issues. But here's the critical reassurance: if the condition is diagnosed within the first few months of life, the chances of typical development are excellent. That's one reason most states require newborn thyroid screening.
How Does It Affect Children and Teens?
In general, children and teens with hypothyroidism have symptoms similar to those in adults. But they also may have poor growth that leads to short stature, delayed development of permanent teeth, delayed puberty, and poor mental development.
When Should You See a Doctor?
See your healthcare professional if you're feeling tired for no reason or if you have other symptoms of hypothyroidism.
If you're taking thyroid hormone medicine for hypothyroidism, follow your healthcare professional's advice on how often you need medical appointments. At first, you may need regular appointments to make sure you're receiving the right dose of medicine. Over time, you may need checkups so that your healthcare professional can monitor your condition and medicine.
What Causes Hypothyroidism?
Hypothyroidism happens when the thyroid gland doesn't make enough of its two main hormones, T-4 and T-3. Conditions or treatments that can lead to hypothyroidism include the following.
Autoimmune disease. The most common cause of hypothyroidism is an autoimmune disease called Hashimoto's disease. Autoimmune diseases happen when the immune system makes antibodies that attack healthy tissues. Sometimes that process involves the thyroid gland and affects its ability to make hormones.
Thyroid surgery. Surgery to remove all or part of the thyroid gland can lower the gland's ability to make thyroid hormones or stop it completely.
Radiation therapy. Radiation used to treat cancers of the head and neck can affect the thyroid gland and lead to hypothyroidism.
Thyroiditis. Thyroiditis happens when the thyroid gland becomes inflamed. This may be due to an infection, or it can result from an autoimmune disease or another medical condition affecting the thyroid. Thyroiditis can trigger the thyroid to release all of its stored thyroid hormone at once. That causes a spike in thyroid activity, a condition called hyperthyroidism. Afterward, the thyroid becomes underactive.
Medicine. Many medicines may lead to hypothyroidism. One such medicine is lithium, which is used to treat some psychiatric conditions. Another is amiodarone. If you're taking medicine, ask your healthcare professional about its effect on the thyroid gland.
Hypothyroidism causes split into main causes — autoimmune disease (Hashimoto's, most common), thyroid surgery, radiation therapy, thyroiditis, and certain medicines — and less common causes — present at birth, pituitary condition, pregnancy, and not enough iodine — plus six risk factors.
What Are the Less Common Causes?
Less often, hypothyroidism may be caused by problems present at birth, a pituitary condition, pregnancy, or not enough iodine:
Less Common Cause | What Happens |
Problems present at birth | Some babies are born with a thyroid that doesn't work correctly or with no thyroid gland; in most cases the reason isn't clear; some children have an inherited form |
Pituitary condition | A relatively rare cause — the pituitary gland fails to make enough thyroid-stimulating hormone (TSH), usually because of a noncancerous pituitary tumor |
Pregnancy | Some people develop hypothyroidism during or after pregnancy; untreated, it raises the risk of pregnancy loss, premature delivery, and preeclampsia, and can seriously affect the developing fetus |
Not enough iodine | The thyroid needs iodine to make hormones; iodine is found in seafood, seaweed, plants grown in iodine-rich soil, and iodized salt. Too little leads to hypothyroidism; too much can make it worse in people who already have it. In the U.S., adding iodine to table salt has almost eliminated this problem |
What Raises Your Risk?
Although anyone can develop hypothyroidism, you're at increased risk if you:
Risk Factor | Why It Matters |
Are assigned female at birth | Women are more likely to develop the condition |
Have a family history of thyroid disease | Genetics play a role in thyroid conditions |
Have an autoimmune disease | Type 1 diabetes or celiac disease raise the risk |
Have received treatment for hyperthyroidism | Overactive-thyroid treatment can swing the pendulum |
Received radiation to your neck or upper chest | Radiation can damage thyroid tissue |
Have had thyroid surgery | Removing part or all of the gland reduces hormone output |
What Happens If Hypothyroidism Goes Untreated?
Hypothyroidism that isn't treated can lead to other health concerns, including:
Complication | What It Is |
Goiter | The thyroid gland becomes larger; a large goiter may cause problems with swallowing or breathing |
Heart conditions | Higher risk of heart disease and heart failure, mainly because an underactive thyroid tends to raise LDL ("bad") cholesterol |
Peripheral neuropathy | Long-untreated hypothyroidism can damage peripheral nerves — the nerves that carry information from the brain and spinal cord to the rest of the body — causing pain, numbness and tingling in the arms and legs |
Infertility | Low thyroid hormone can interfere with ovulation; some causes, such as autoimmune diseases, also can harm fertility |
Birth defects | Babies born to people with untreated thyroid disease may have a higher risk of birth defects; untreated congenital hypothyroidism risks serious physical and mental development issues, but early diagnosis (within the first few months) makes typical development likely |
Myxedema coma | A rare, life-threatening condition from long-untreated hypothyroidism; may be triggered by sedatives, infection or other stress. Symptoms include intense cold intolerance and drowsiness, followed by extreme lack of energy and then unconsciousness. Requires emergency medical treatment |
How Is Hypothyroidism Diagnosed?
The symptoms of hypothyroidism can be different from person to person. And they often look like symptoms of other health issues. Because of that, a diagnosis of hypothyroidism doesn't rely on symptoms alone. It's usually based on the results of blood tests.
The first blood test typically done to diagnose hypothyroidism measures the level of thyroid-stimulating hormone (TSH) in the blood. If it's high, the test is done again, along with a blood test for the thyroid hormone T-4. If the results show that TSH is high and T-4 is low, then the diagnosis is hypothyroidism. In some cases, the thyroid hormone T-3 may be measured as well.
If the second test shows high TSH but T-4 and T-3 are in the standard range, then the diagnosis is a condition called subclinical hypothyroidism. It usually doesn't cause any noticeable symptoms.
TSH tests also play an important role in managing hypothyroidism over time. They help your healthcare professional find and maintain the right dosage of medicine for you.
One practical note before your blood draw: the results of these blood tests can be affected by some medicines or supplements. This includes biotin, a vitamin taken as a stand-alone supplement or as part of a multivitamin. Before you have blood tests done, tell your health professional about any medicines or supplements you take.
Test Result Pattern | What It Means |
High TSH + low T-4 | Hypothyroidism — confirmed |
High TSH + normal T-4 and T-3 | Subclinical hypothyroidism — usually no noticeable symptoms |
TSH normal | Hypothyroidism unlikely on hormone testing |
The four-stage pathway — Blood Test (TSH), Diagnosis, Daily Medicine, Ongoing Monitoring — with a note that you'll feel better in 1–2 weeks and should take the medicine correctly, never stopping without guidance.
How Is Hypothyroidism Treated?
Treatment for hypothyroidism usually includes taking the thyroid hormone medicine levothyroxine (Levo-T, Synthroid, others) every day. This medicine is taken by mouth. It returns hormone levels to a healthy range, eliminating symptoms of hypothyroidism.
You'll likely start to feel better one or two weeks after you begin treatment. Treatment with levothyroxine likely will be lifelong. Because the dosage you need may change, your healthcare professional may check your thyroid-stimulating hormone (TSH) level every year.
How Do You Find the Right Dosage?
To find the right dosage of levothyroxine for you, your healthcare professional checks your level of TSH about 6 to 8 weeks after you start taking the medicine. You may need another blood test to check TSH again six months later. After that, you may need it checked about once a year.
Too much levothyroxine can cause side effects, such as tiredness, increased appetite, sleep problems, shakiness, and a pounding of the heart sometimes called heart palpitations. Levothyroxine typically causes no side effects when used in the correct dose.
If you change brands of the medicine, tell your healthcare professional, as the dosage may need to change.
If you have coronary artery disease or severe hypothyroidism, your healthcare professional may start treatment with a smaller amount of medicine and then slowly increase the dosage. This allows your heart to adjust to the rise in your body's metabolism.
How Should You Take Levothyroxine?
Taking the medicine correctly matters as much as taking it daily.
Levothyroxine is best taken on an empty stomach. Ideally, you take the hormone in the morning with water and then wait 30 to 60 minutes before you eat. If you take the medicine at bedtime, wait to take it until at least four hours after your last meal or snack.
Don't skip doses or stop taking the medicine because you feel better. If you do, it's likely that the symptoms of hypothyroidism will slowly return. If you miss a dose of levothyroxine, take two pills the next day.
Some medicines, supplements and even some foods may affect your body's ability to absorb levothyroxine. Talk to your healthcare professional if you eat large amounts of soy products, or if you typically eat a high-fiber diet. Also tell your provider if you take other medicines, especially iron supplements or multivitamins that have iron, aluminum hydroxide (found in some antacids), and calcium supplements.
Taking It Right | The Rule |
Morning timing | Take with water on an empty stomach; wait 30–60 minutes before eating |
Bedtime timing | Wait at least four hours after your last meal or snack |
Missed dose | Take two pills the next day |
Stopping | Don't stop because you feel better — symptoms will slowly return |
Brand changes | Tell your healthcare professional — the dosage may need to change |
Absorption blockers | Discuss soy, high-fiber diets, iron, calcium supplements, and some antacids with your provider |
What About Subclinical Hypothyroidism?
If you are diagnosed with subclinical hypothyroidism, talk about treatment with your healthcare professional. For a mild rise in TSH, thyroid hormone medicine may not be useful. If your TSH level is higher but still in the subclinical range, thyroid hormones may improve some symptoms.
What About "Natural" Thyroid Supplements?
Most healthcare professionals recommend taking the medicine levothyroxine to treat hypothyroidism. But an extract with thyroid hormone derived from the thyroid glands of pigs is available. It is sometimes called desiccated thyroid extract. However, this treatment is not recommended because the amount of T-4 and T-3 in it may not be consistent from batch to batch. It is not safe for pregnant people to take desiccated thyroid extract because it can harm a fetus's development.
How Should You Prepare for Your Appointment?
You'll likely start by seeing your primary healthcare professional. Or you may be referred to a specialist in hormone conditions, called an endocrinologist. Infants with hypothyroidism need to see a pediatric endocrinologist right away. Children or teens can start with their primary health professional. But they need to see a pediatric endocrinologist if there are any questions about levothyroxine or about the correct dosage of the medicine.
What you can do. Be aware of any restrictions before your appointment — when you make the appointment, ask if there's anything you need to do before you arrive. Write down any symptoms you're experiencing, including any that may seem unrelated to the reason you scheduled the appointment. Write down key personal information, including any major stresses or recent life changes. Make a list of all medicines, vitamins or supplements you're taking. Take a family member or friend along, if possible — someone who goes with you may remember something that you missed or forgot. And write down questions to ask your healthcare professional.
Questions to ask might include: What's the most likely cause of my symptoms? What tests do I need? Is my condition likely temporary or long-lasting? What treatments are available, and which do you recommend? I have other health conditions — how can I best manage them together? Are there restrictions I need to follow? Should I see a specialist? Is there a generic alternative to the medicine you're prescribing? Are there brochures or other printed material I can take with me? What websites do you recommend? Don't hesitate to ask other questions.
What to expect from your doctor. Your healthcare professional is likely to ask a number of questions, including: When did you begin experiencing symptoms? Have your symptoms been continuous or occasional? How severe are your symptoms? What, if anything, seems to improve your symptoms? What, if anything, makes your symptoms worse? Do you have a family history of thyroid disease?
Conclusion: A Slow-Moving Condition With a Fast, Simple Fix
Hypothyroidism earns its nickname — underactive thyroid — because everything it touches slows down. Fatigue, cold sensitivity, weight gain, and brain fog creep in so gradually that many people write them off as normal aging. The good news is that once it's identified, hypothyroidism is one of the most straightforward conditions in all of medicine to manage.
A simple blood test confirms the diagnosis. A daily thyroid hormone pill restores your levels, and most people feel meaningfully better within a week or two. The ongoing work is small: take the pill on an empty stomach, never stop cold turkey when you feel better, and keep your yearly TSH checkups. Done consistently, that routine keeps the risks of untreated hypothyroidism — heart disease, nerve damage, infertility, and the rare myxedema coma — off the table.
Three practical takeaways. First, if you're exhausted for no clear reason, ask for a TSH blood test — it's cheap, simple, and definitive. Second, once you start levothyroxine, take it every morning on an empty stomach and don't stop when you feel better. Third, bring a full list of your medicines, vitamins, and supplements to every appointment, since biotin, iron, and calcium can all affect your results and your absorption.
Call to action: Book a conversation with your healthcare professional and bring this guide's question list to the appointment.
Frequently Asked Questions
What is hypothyroidism?
Hypothyroidism — also called underactive thyroid — happens when the thyroid gland doesn't make enough thyroid hormone. The thyroid is a small, butterfly-shaped gland at the base of the neck that makes two main hormones, T-4 and T-3, which affect every cell in the body and control metabolism, body temperature, and heart rate.
What are the early signs of hypothyroidism?
Early signs are easy to miss: tiredness, more sensitivity to cold, constipation, dry skin, and weight gain. Over time, symptoms can progress to a puffy face, hoarse voice, coarse or thinning hair, muscle weakness and aches, heavier or irregular periods, a slowed heart rate (bradycardia), depression, and memory problems.
How is hypothyroidism diagnosed?
It's diagnosed with blood tests, not symptoms alone. The first test measures thyroid-stimulating hormone (TSH). If TSH is high, it's rechecked along with T-4. High TSH plus low T-4 confirms hypothyroidism. If T-4 and T-3 are normal despite high TSH, the diagnosis is subclinical hypothyroidism, which usually has no noticeable symptoms.
What causes hypothyroidism?
The most common cause is an autoimmune disease called Hashimoto's disease, in which the immune system attacks the thyroid. Other causes include thyroid surgery, radiation therapy to the head or neck, thyroiditis (inflammation that first spikes hormone levels, then leaves the gland underactive), and medicines such as lithium and amiodarone.
Can hypothyroidism go away on its own?
Treatment with levothyroxine likely will be lifelong for most people. Don't stop taking the medicine because you feel better — the symptoms will slowly return. Your dosage may change over time, which is why TSH is typically rechecked every year.
How should I take levothyroxine?
On an empty stomach, ideally in the morning with water, waiting 30 to 60 minutes before eating. If taken at bedtime, wait at least four hours after your last meal. If you miss a dose, take two pills the next day. Tell your healthcare professional before changing brands, and flag any soy products, high-fiber diet, iron, calcium supplements, or antacids, since these can affect absorption.
Is "natural" desiccated thyroid extract a safe alternative?
It's not recommended. Desiccated thyroid extract — derived from pig thyroid glands — can have inconsistent amounts of T-4 and T-3 from batch to batch. It is not safe for pregnant people because it can harm a fetus's development. Most healthcare professionals recommend levothyroxine.
What happens if hypothyroidism is left untreated?
Untreated hypothyroidism can raise cholesterol and heart disease risk, cause an enlarged thyroid (goiter), damage peripheral nerves, interfere with ovulation and fertility, and raise the risk of birth defects. Rarely, long-untreated hypothyroidism leads to myxedema coma — a life-threatening emergency requiring immediate medical treatment.
Can hypothyroidism affect pregnancy and infants?
Yes. Hypothyroidism that develops during or after pregnancy raises the risk of pregnancy loss, premature delivery, and preeclampsia if untreated, and can seriously affect the developing fetus. Infants born with hypothyroidism usually have no symptoms at first, which is why most states require newborn thyroid screening — and if diagnosed within the first few months, the chances of typical development are excellent.
Related Reading
References
Hypothyroidism (underactive thyroid) — Symptoms & causes. mayoclinic.org
Hypothyroidism (underactive thyroid) — Diagnosis & treatment. mayoclinic.org
Disclaimer: This article is for general educational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. Always seek the guidance of your healthcare professional with any questions about a medical condition. In a medical emergency, call 911 or your local emergency number.
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