Hypothyroidism Symptoms, Causes, Diagnosis and Treatment

Introduction

Hypothyroidism occurs when the thyroid does not make enough hormone for the body’s needs^[1]. It is also called an underactive thyroid^[1,2]. Low thyroid hormone can slow many body functions^[1,9].

Symptoms may be mild and easy to miss^[1,7]. They can also look like signs of other health problems^[6,10]. For this reason, symptoms alone cannot confirm the condition^[6,10].

This guide covers hypothyroidism symptoms, causes, diagnosis and treatment. It also explains blood tests, pregnancy care, daily management, and urgent warning signs.

Overview: What Is Hypothyroidism?

The thyroid is a small gland at the front of the neck^[1]. It has a shape like a butterfly^[1]. The gland makes hormones that control how the body uses energy^[1,2].

This use of energy is called metabolism^[2]. Thyroid hormones affect almost every organ in the body^[1,9]. They even affect how the heart beats^[1].

When hormone levels fall, many body processes slow down^[1,9]. A person may feel tired, cold, constipated, or low in mood^[3,7]. The number and strength of symptoms can vary^[7].

How an underactive thyroid affects the body

Thyroid hormones help control energy use and heart function^[1,9]. They also affect digestion, body heat, skin, muscles, mood, and menstrual periods^[1,7].

Underactive thyroid symptoms often appear slowly^[7]. Some people notice few changes during the early stages^[1,7]. Others develop symptoms that affect work, sleep, or daily tasks.

Types of hypothyroidism

Doctors group hypothyroidism by where the problem starts:

• Primary hypothyroidism begins in the thyroid gland^[4]. The gland cannot make enough thyroid hormone^[4].
• Central hypothyroidism starts with a problem in the pituitary gland or hypothalamus^[4]. These are parts of the brain that help control thyroid function^[4].
• Subclinical hypothyroidism may cause a high TSH level with normal thyroid hormone levels^[6].
• Congenital hypothyroidism is present at birth^[2].

Central hypothyroidism is rare compared with primary hypothyroidism^[4]. The pituitary gland normally makes thyroid-stimulating hormone, or TSH^[6]. TSH tells the thyroid to make hormone^[6].

How common hypothyroidism is and who is at risk

Nearly 5 out of 100 Americans aged 12 and older have hypothyroidism^[1]. Many cases are mild or cause few symptoms^[1].

The condition is more common in women and older adults^[1,2]. Risk is also higher in people with a family history of thyroid disease^[1]. People with an autoimmune disease also have a higher risk^[1].

An autoimmune disease causes the immune system to attack the body’s own tissue^[3,9]. Past thyroid treatment may also raise the risk of hypothyroidism^[1,9]. This includes thyroid surgery and radioactive iodine treatment^[1,9].

Radiation aimed at the neck can damage the thyroid^[1]. Some medicines can also affect thyroid function^[1,2].

Symptoms and Warning Signs

Hypothyroidism symptoms vary with the level of hormone loss^[7]. They often develop over months or years^[7]. Early symptoms may be hard to notice^[1,7].

Many other health problems cause similar symptoms^[6,10]. No single symptom proves that a person has hypothyroidism^[6,10]. Blood tests are needed to make the diagnosis^[6,10].

Common symptoms in adults

Common underactive thyroid symptoms include:

• Tiredness or low energy^[7,10]
• Greater sensitivity to cold^[7,10]
• Constipation^[3,7,10]
• Dry skin or other skin changes^[3,10]
• Weight gain without a clear cause^[7,10]
• Muscle weakness or aches^[7]
• Low mood or depression^[3,7]
• Slow thinking or memory problems^[7]
• A hoarse voice^[7,10]
• Changes in menstrual periods^[7]

Fatigue and weight gain are not unique to hypothyroidism^[8]. Many other conditions can cause them^[6,8]. A blood test can show whether the thyroid may be involved^[8].

Symptoms can become clearer as the body slows down^[7]. Long-term untreated disease may lead to high cholesterol and heart problems^[7].

Symptoms in children, older adults, and during pregnancy

Hypothyroidism can affect people of different ages^[1,2]. Its signs may be mild or unclear^[1,7]. Testing is important when symptoms or risk factors point to thyroid disease^[1,6].

Older adults may view fatigue or slow thinking as part of aging^[7]. However, these changes can also occur with hypothyroidism^[7]. A health professional can decide if thyroid testing is needed.

Hypothyroidism during pregnancy can pose risks to the pregnant person and baby^[1]. Pregnancy may also increase the body’s need for thyroid hormone^[1]. People who are pregnant should discuss thyroid care with their medical team^[1].

This advice also applies to those who plan to become pregnant^[1]. People already taking thyroid medicine need follow-up during pregnancy^[1].

Congenital hypothyroidism starts at birth^[2]. A baby or child with possible thyroid disease needs medical review. Blood tests help doctors check thyroid function^[6,10].

Possible complications

Untreated hypothyroidism can cause other health problems^[1,7]. These may include high cholesterol and heart disease^[7]. The risk can rise as the condition becomes more severe^[7].

Myxedema coma is a rare and life-threatening complication^[8,10]. It can occur with severe hypothyroidism^[8,10]. The person may not be in a coma when symptoms first appear.

Urgent warning signs include:

• Severe confusion^[8,10]
• Extreme sleepiness or poor response^[8,10]
• Slow breathing^[8,10]
• Very low body temperature^[8,10]

Severe untreated hypothyroidism can be fatal^[8,10]. Call emergency services if these warning signs occur.

Causes and Risk Factors for Hypothyroidism

Many health problems and treatments can reduce thyroid hormone output^[1,2]. Some damage the gland itself^[1,9]. Others affect the signals that control it^[4].

Hashimoto’s disease and thyroid inflammation

Hashimoto’s autoimmune thyroiditis is the most common cause in places with enough iodine^[3,4]. Iodine deficiency is a major cause of hypothyroidism worldwide^[4].

Hashimoto’s disease causes the immune system to attack the thyroid^[3,9]. This attack slowly harms thyroid tissue^[3,9]. The damaged gland may stop making enough hormone^[3].

Thyroiditis means swelling or inflammation of the thyroid^[2]. This inflammation can harm the cells that make hormones^[2]. Some forms can occur after an infection or pregnancy^[2].

A personal or family history of autoimmune disease can raise the risk^[1]. However, risk factors do not prove that someone has hypothyroidism. Blood tests are still needed for diagnosis^[6,10].

Thyroid surgery, radiation, and medicines

Surgery may remove part or all of the thyroid^[1,9]. This can cause hypothyroidism if too little working tissue remains^[1,9].

Radioactive iodine treatment can also cause an underactive thyroid^[9]. Doctors may use this treatment for an overactive thyroid^[9]. Radiation aimed at the neck may harm thyroid cells^[1].

Some medicines can change thyroid function^[1,2]. A person should not stop a prescribed drug without medical advice. A clinician can review the drug and decide whether blood tests are needed.

Iodine imbalance

The thyroid needs iodine to make thyroid hormone^[1]. Too little iodine is a major cause of hypothyroidism worldwide^[4].

Too much iodine can also affect thyroid function in some people^[1]. Do not start iodine supplements as a form of self-treatment. Ask a health professional whether you need them.

Food or supplements cannot replace prescribed hormone when the thyroid makes too little. Diet should support medical treatment rather than replace it.

Postpartum, congenital, and central hypothyroidism

Postpartum thyroiditis occurs after pregnancy^[2]. It involves inflammation of the thyroid gland^[2]. Blood tests can help assess thyroid function^[6,10].

Congenital hypothyroidism is present when a baby is born^[2]. It is different from thyroid disease that begins later in life.

Central hypothyroidism starts outside the thyroid gland^[4]. It results from a problem in the pituitary gland or hypothalamus^[4]. This form is rare^[4].

Central hypothyroidism needs a careful medical review^[4]. Doctors must look for disease affecting the pituitary gland or hypothalamus^[4].

Diagnosis: Hypothyroidism Blood Tests and Evaluation

Doctors diagnose hypothyroidism mainly with blood tests^[6,10]. Symptoms alone are not enough because they have many possible causes^[6,10].

A clinician also reviews the person’s health history. This helps place the test results in context.

Medical history and physical examination

A health professional may ask when symptoms began. The clinician may also ask whether they have changed over time.

The medical review may cover past thyroid care and neck radiation. It may also include pregnancy, medicines, autoimmune disease, and family history.

A physical exam can show signs linked with thyroid disease. However, physical signs cannot confirm hypothyroidism on their own^[10]. Early signs are often broad and unclear^[10].

TSH and free T4 blood tests

TSH is often the first blood test used for possible primary hypothyroidism^[6]. TSH comes from the pituitary gland^[6]. It tells the thyroid to make hormone^[6].

Free T4 is the available form of thyroxine in the blood. Thyroxine is one of the main thyroid hormones. Clinicians often check T4 when TSH is abnormal^[6,10].

Primary overt hypothyroidism usually causes high TSH and low free T4^[4,6]. Central hypothyroidism can cause low free T4 with low or normal TSH^[4]. In this setting, a normal TSH is too low for the low free T4 level^[4].

Some clinicians may use thyroid antibody blood tests when they suspect autoimmune thyroid disease. These tests can help support Hashimoto’s disease as the cause.

Overt and subclinical hypothyroidism

Overt hypothyroidism means there is a clear lack of thyroid hormone. In primary disease, high TSH and low free T4 support this diagnosis^[6].

Subclinical hypothyroidism often causes high TSH with normal T4 and T3 levels^[6]. It may cause no clear symptoms^[6]. A clinician may repeat the tests before making a treatment plan.

Test ranges can differ between labs. A health professional should review the full results. One test number should not be judged on its own.

Diagnosing central hypothyroidism

A TSH test alone may miss central hypothyroidism^[4]. The free T4 may be low while TSH is low or seems normal^[4].

This happens because the brain is not sending the expected signal^[4]. Central hypothyroidism requires a review for pituitary or hypothalamic disease^[4]. Doctors use the full clinical picture to plan more tests.

Treatment and Daily Management

Levothyroxine remains the standard treatment for hypothyroidism^[5]. It replaces T4 that the thyroid cannot make in enough amounts^[5].

Other thyroid hormone products have not shown steady benefits over levothyroxine for routine care^[5]. Treatment is often safe and effective after the correct dose is found^[7]. Most people can manage the condition with medicine and follow-up visits^[8].

Levothyroxine treatment and follow-up

The right levothyroxine dose differs from person to person^[6,10]. Doctors use blood tests to choose and maintain the dose^[6].

Age and heart health can affect how treatment begins^[10]. Pregnancy may also change how much thyroid hormone a person needs^[1]. Patients should take only the dose prescribed for them.

TSH tests help guide long-term care for primary hypothyroidism^[6]. Follow-up results show whether a dose change may be needed^[6].

Too little medicine may leave the condition undertreated. Patients should not change or stop levothyroxine without medical advice.

Medication timing and interactions

Food can affect how the body takes in levothyroxine. Patients should follow the timing directions from their care team.

Iron, calcium, antacids, and some medicines may reduce how much levothyroxine the body takes in. A doctor or pharmacist can explain how to space these products.

Patients should share a full list of medicines and supplements. This includes prescribed drugs, vitamins, and nonprescription products. The list can help the care team check for interactions.

Persistent symptoms

Some people still feel unwell while taking levothyroxine^[5]. Ongoing fatigue or low mood may have a cause other than thyroid disease. Weight changes can also have other causes^[6,8].

A clinician can review medicine use and blood test results. The review can show whether thyroid treatment is working as planned.

Alternative thyroid products are not clearly better than levothyroxine for routine treatment^[5]. Patients should not switch products without medical care. Any change may require new testing and close follow-up.

Diet and iodine

No special food plan can replace needed thyroid hormone. People should take their medicine in a steady way.

Iodine is needed to make thyroid hormone^[1]. Yet too little or too much iodine can cause thyroid problems^[1,4]. Avoid iodine or kelp supplements unless a health professional recommends them.

Pregnancy and long-term outlook

Hypothyroidism during pregnancy can pose risks for the patient and baby^[1]. Pregnancy can increase thyroid hormone needs^[1].

People taking levothyroxine should contact their clinician when they become pregnant^[1]. They should also seek advice when planning a pregnancy^[1]. Blood tests help guide care during this time^[1,6].

Hypothyroidism is often manageable with the right dose and regular care^[7,8]. Many patients need long-term hormone replacement and follow-up^[8].

When to See a Doctor

Make an appointment for lasting fatigue, cold sensitivity, or constipation. Also seek care for dry skin, weight gain, muscle weakness, or menstrual changes. These symptoms have many causes, so blood tests are needed^[6,10].

Seek medical advice if you:

• Have symptoms and a family history of thyroid disease^[1]
• Have an autoimmune condition^[1]
• Had thyroid surgery or radioactive iodine treatment^[1,9]
• Received radiation aimed at the neck^[1]
• Are pregnant or plan to become pregnant^[1]
• Recently gave birth and have possible thyroid symptoms^[2]
• Take medicine that may affect thyroid function^[1,2]
• Still have symptoms while taking levothyroxine^[5]

Call emergency services for severe confusion or extreme sleepiness^[8,10]. Slow breathing and very low body temperature also need urgent care^[8,10]. These signs may point to a life-threatening form of severe hypothyroidism^[8,10].

Conclusion

Learning about hypothyroidism symptoms, causes, diagnosis and treatment can support timely care. Symptoms alone cannot confirm the condition^[6,10]. Many of them also occur with other health problems^[6,10].

TSH and free T4 blood tests play a key role in diagnosis^[6,10]. Hashimoto’s disease is the main cause in places with enough iodine^[3,4]. Iodine deficiency remains a major cause worldwide^[4].

Levothyroxine is the standard treatment for hypothyroidism^[5]. Most patients can manage the condition with the right dose and regular follow-up^[7,8]. Consistent medicine use also supports effective long-term care.