Thyroid Disorders

Hyperthyroidism and Hypothyroidism

Image of an endocrinologist and a patient.

The Thyroid Gland

The thyroid is a small butterfly-shaped gland located at the base of your neck (just below the voice box, or larynx).

The thyroid gland is a vital part of the endocrine system. It’s responsible for producing two important hormones: triiodothyronine (T3) and thyroxine (T4).

These hormones regulate the rate at which processes in the body (e.g., breathing, contracting muscles) converts and uses energy (metabolism).

Did You Know?

  • Women are 5-8 times more likely to have a thyroid problem.
  • Approximately 20 million Americans currently have some form of thyroid disease.
  • Undiagnosed thyroid disease can increase risk for osteoporosis, infertility and cardiovascular disease.
  • Pregnant women with undiagnosed hypothyroidism have an increased risk for preterm delivery, developmental problems (in baby), and miscarriage.

Do You Have Thyroid Disease?

Diagnosing thyroid disease can be tricky, as the symptoms associated with thyroid disease can overlap and be confused with many different health problems.

To determine if you have a thyroid condition, your doctor may perform a:

  1. Physical exam
  2. Thyroid stimulating hormone (TSH) test
    Depending on results of TSH test, additional blood tests may be needed to check the levels of one or both of your T3 and T4 hormones.
  3. Radioactive iodine uptake or thyroid scan

What is Thyroid-Stimulating Hormone (TSH)?

TSH is produced by the pituitary gland and helps regulate thyroid hormone production. When thyroid hormone levels drop or rise, the pituitary gland responds by dropping or raising TSH.

In most situations, the TSH test is the most accurate test for diagnosing both hyperthyroidism and hypothyroidism.  

Family History Risk Factor

If a family member has thyroid disease, you have a higher chance of developing the disease at some point in your life. If you believe that you are having symptoms, it's recommended that you come in for a screening.

What Kind of Doctor Should You See?

While many primary care physicians can diagnose and treat mild hyperthyroidism, hypothyroidism and thyroiditis, cases in which symptoms are severe and do not resolve on their own within a few months should be assessed by an endocrinologist.

“More than 12 percent of the U.S. population will develop a thyroid condition during their lifetime.”
- American Thyroid Association

Overactive Thyroid Gland (Hyperthyroidism)

When the thyroid gland produces too much thyroid hormone, this is known as hyperthyroidism.


Many conditions can cause hyperthyroidism. These include:

  • Graves disease (most common cause)
  • Thyroid inflammation (thyroiditis) due to viral infections, autoimmune conditions, or postpartum period
  • Overactive thyroid nodules (toxic multinodular goiter, or toxic adenomas)
  • Medical imaging tests that use iodine
  • Tumors of the ovaries or testes (extremely rare)
  • Eating excess amounts of iodine-containing foods
  • Consuming large amounts of thyroid hormone

Graves’ Disease

Graves’ disease is the leading cause of hyperthyroidism.

Graves’ disease is an autoimmune condition where your own immune system triggers your thyroid to overproduce thyroid hormone. It is most common in women over the age of 20, but can occur in men too.


Symptoms that can occur with an overactive thyroid gland:

  • Infertility
  • Excessive fatigue
  • Weight loss (weight gain is rare)
  • Irritability
  • Rapid speech 
  • Anxiety
  • Muscle weakness
  • Irregular periods
  • Vision problems
  • Heat intolerance
  • Sleep problems
  • Protruding eyes
  • Excessive sweating
  • High blood pressure
  • Irregular or increased heartbeat
  • Increased bowel movement


An overactive thyroid can be treated in a few different ways.

  1. Radioactive iodine: Stops hormone production by destroying the thyroid gland.
  2. Antithyroid medications: Slows down hormone production.
  3. Thyroid surgery: Part of or all of the thyroid gland is removed.

Possible Complications of Hyperthyroidism

Graves' Ophthalmopathy (Thyroid Eye Disease)

Thyroid disease can impact many parts of the eye and surrounding eye area. This is known as thyroid eye disease, Graves' eye disease, Graves' ophthalmopathy, or Graves' orbitopathy.

Common eye symptoms include:

  • Redness
  • Bulging eyes
  • A "stare"
  • Dryness
  • Double vision
  • Swelling of the eyelids

Thyroid eye disease is treated at UC San Diego Shiley Eye Center.

Thyrotoxicosis and Thyroid Storm

When you have an excess amount of thyroid hormone in your body, this is known as thyrotoxicosis.

Anyone who has severe thyrotoxicosis, such as those with Graves' disease, have a high risk for thyroid storm. Thyroid storm is a severe manifestation of thyrotoxicosis, in some cases even leading to heart failure and abnormal buildup of fluid in the lungs, known as pulmonary edema. Mortality rate of thyroid storm is between 20 to 30 percent.

Symptoms of thyroid storm include:

  • Pounding heart
  • Shaking
  • Diarrhea
  • Sweating
  • Confusion
  • Increased temperature

Thyroid storm is a life-threatening, emergency condition.
It requires immediate medical attention.

Underactive Thyroid Gland (Hypothyroidism)

Hypothyroidism occurs when your thyroid gland is underactive or doesn’t produce enough hormones to meet the body’s needs. Many body functions require the hormones produced by your thyroid gland. Without them, functions slow down.

Who's At Risk

While hypothyroidism is most common in women 50 or older, it can occur in anyone – man or woman – at any age. People who have a parent or grandparent with an autoimmune disease also have an increased risk.


The most common cause of hypothyroidism in adults is autoimmune thyroiditis (Hashimoto's disease). In people with Hashimoto's disease, the body's own immune system inhibits the thyroid gland from producing thyroid hormone.

Other forms of thyroiditis that can lead to hypothyroidism include:

  • Subacute thyroiditis from a viral infection
  • Postpartum thyroiditis after pregnancy

Hypothyroidism can also result from:

  • Certain medications
  • Radioactive iodine treatment
  • Thyroid removal by surgery
  • Pituitary dysfunction
  • Failure of the thyroid gland to form during development


The symptoms of hypothyroidism can be vague and overlap with many other medical conditions. 

Symptoms of hypothyroidism include:

  • Sluggishness
  • Heavy menstrual periods
  • Brittle nails
  • Fatigue
  • Unexplained weight gain
  • Slow heart rate
  • Constipation or hard stools
  • Depression or sadness
  • Numbness or tingling of the hands
  • Dry thinning hair
  • Dry skin or paleness
  • Joint pain and muscle aches
  • Sensitivity to cold temperature


To diagnose an underactive thyroid, your TSH level will need to be checked. In certain cases, your T4 and/or T3 level may also be checked.


Unlike hyperthyroidism treatment, which aims to destroy/stop hormone production, treatment for hypothyroidism includes replacing the hormone which you are lacking. Medicine for an underactive thyroid usually needs to be taken for life.

There are various forms of thyroid hormone available. Your provider will work with you to find the best thyroid hormone replacement. ​bulletLearn about synthetic thyroid hormone, levothyroxine, in our Health Library.

Possible Complications of Hypothyroidism

Not treating hypothyroidism can result in health problems such as: 

  • Goiter: A goiter, or enlarged thyroid gland, can occur from constant stimulation of the thyroid to make more hormones. In severe cases, this can interfere with swallowing or breathing.
  • Infertility: Untreated hypothyroidism in women of childbearing age can lead to infertility or miscarriage, and/or severe birth defects to babies born to hypothyroid mothers.
  • Myxedema: In severe cases of long-term undiagnosed or untreated hypothyroidism, an extremely rare, life-threatening condition called myxedema coma can occur. Symptoms include lethargy, altered mental status and loss of consciousness.