Your thyroid is a small gland at the base of the front of your neck. Hypothyroidism, also known as underactive thyroid disease, is a common condition that occurs when the thyroid gland doesn’t create the proper amount of thyroid hormones. The lack of thyroid hormone in the bloodstream causes your metabolism to slow down, impacting your entire body and causing symptoms like fatigue and weight gain.

What causes hypothyroidism?

Hypothyroidism is most commonly caused by an autoimmune disorder, meaning your immune system begins to attack normal tissues. In hypothyroidism, your body starts to make antibodies against the thyroid gland, flooding it with white blood cells and scar tissue.

Hypothyroidism is treatable

Many types of hypothyroidism can be cured. In fact, effective treatment is available for all types of hypothyroidism.

Not all cases of hypothyroidism require treatment, however, especially if they’re mild. Some cases have resolved without treatment.

Symptoms of hypothyroidism

Hypothyroidism symptoms are wide ranging and typically develop slowly over time. In some cases, they can take years to advance. Some of the most common symptoms include:

  • Being unable to tolerate cold temperatures.
  • Experiencing decreased sexual interest.
  • Experiencing numbness and tingling in your hands.
  • Experiencing soreness throughout your body (can include muscle weakness).
  • Feeling depressed.
  • Feeling more forgetful (“brain fog”).
  • Feeling tired (fatigue).

  • Gaining weight.
  • Having constipation.
  • Having dry, coarse skin and hair.
  • Having frequent and heavy menstrual periods.
  • Having higher than normal blood cholesterol levels.
  • Having your voice become lower and hoarser.
  • Seeing physical changes in your face (including drooping eyelids, as well as puffiness in the eyes and face).

Causes of hypothyroidism

Hypothyroidism is most commonly caused by an autoimmune disorder, meaning your immune system begins to attack normal tissues. In hypothyroidism, your body starts to make antibodies against the thyroid gland, flooding it with white blood cells and scar tissue.

There are primary causes and secondary causes of hypothyroidism. A primary cause is something that directly causes the thyroid to produce low levels of thyroid hormones while a secondary cause involves a failure in the pituitary gland.

Primary causes of hypothyroidism are much more common, with most common primary cause being Hashimoto’s disease, an autoimmune disorder. This hereditary condition causes the body’s immune system to turn on and impair the thyroid, ultimately preventing it from creating and circulating enough thyroid hormone.

The other primary causes of hypothyroidism can include:

  • Hereditary conditions (a medical condition passed down through your family).
  • Iodine deficiency (not having enough iodine – a mineral your thyroid uses to make hormones – in your body).
  • Thyroiditis (inflammation of the thyroid).
  • Treatment of hyperthyroidism (radiation and surgical removal of the thyroid).

Provider and patient having a discussion

How is hyperthyroidism diagnosed?

Female doctor consulting with older woman patient

Due to advancements in testing, doctors are now able to diagnose disorders of the thyroid much earlier than ever before. In spite of the advancements in testing, hypothyroidism can still be difficult to diagnose because its symptoms are often generic enough that they are mistaken for other conditions. For that reason, the best way to diagnose hypothyroidism is with a blood test called the thyroid stimulating hormone (TSH) test. It can detect hypothyroidism by showing your levels of thyroxine and TSH. If your thyroxine levels are low and your TSH levels are high, then you have hypothyroidism.

Your TSH levels become elevated due to your pituitary gland producing more TSH in an effort to make your thyroid gland produce more thyroid hormone. Your doctor will also use your TSH test results to help manage your hypothyroidism, including determining the right dosage of medication, both initially and over time.

Treating hypothyroidism

Because it’s a lifelong disease, treating hypothyroidism will require you taking oral medication that will restore adequate hormone levels for the rest of your life. One of the most commonly prescribed treatments is a medication called levothyroxine. It works by increasing the amount of thyroid hormone your body produces, helping to even out your levels and reverse the signs and symptoms of hypothyroidism.

With careful management, and follow-up appointments with your healthcare provider to make sure your treatment is working properly, you can lead a normal and healthy life.

Male patient listening to doctor

Frequently asked questions (FAQs) about hypothyroidism

Hypothyroidism is a condition in which the thyroid gland doesn’t produce enough thyroid hormone.

Hyperthyroidism is a condition in which the thyroid gland produces too much thyroid hormone.

Hypothyroidism is a fairly common condition, afflicting about 10 million people in the United States. Almost 5% of Americans over 12 years of age have been diagnosed with hypothyroidism.

In most cases, yes. Hypothyroidism tends to occur in family members, so people who have relatives with thyroid disease should monitor themselves for symptoms and consider taking occasional tests.

If left untreated, hypothyroidism can cause some weight gain, mostly due to your metabolism slowing due to the lack of thyroid hormone. In general, the more severe the hypothyroidism, the greater the weight gain.

Yes. Hypothyroidism can cause high blood pressure (also known as hypertension) in patients because of increased peripheral vascular resistance.

Yes. About half of the people with hypothyroidism experience hair loss in some form, ranging from minimal to widespread.

Hypothyroidism negatively impacts the unique growth cycle of individual hair follicles, causing possible hair loss. Other hair changes can also be seen in hypothyroidism, including dry, brittle, and coarse hair that may take longer to grow.

Yes. Headache is one of the most common symptoms of hypothyroidism, occurring in approximately one-third of patients.

In extreme cases, yes. When thyroid hormone drops to extremely low levels, a life-threatening condition called myxedema can occur. Myxedema is the most severe form of hypothyroidism. A person with myxedema can lose consciousness or go into a coma. The condition can also cause the body temperature to drop very low, which can cause death.

MedlinePlus: National Library of Medicine. Hypothyroidism (https://medlineplus.gov/hypothyroidism.html)

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Hypothyroidism (Underactive Thyroid) (https://www.niddk.nih.gov/health-information/endocrine-diseases/hypothyroidism)

The Office on Women’s Health (OWH). Thyroid disease (https://www.womenshealth.gov/a-z-topics/thyroid-disease)