Hyperthyroidism vs. Hypothyroidism: What’s the Difference?

Updated: Mar. 24, 2021

Learn the difference between hyperthyroidism and hypothyroidism, and what to do if you may have thyroid disease.

Located in the front lower portion of the neck, the butterfly-shaped thyroid gland is small. But its impact on the body’s normal functioning is big. (Need proof? Just check out these 13 fascinating thyroid facts.) More than 12 million Americans will have a thyroid-related condition in his or her life, according to the American Thyroid Association (ATA), and a whopping 60 percent of these remain undiagnosed. An overactive thyroid (hyperthyroidism) and underactive thyroid (hypothyroidism), are two of the most common thyroid-related conditions—and tough to spot.

Read on to learn the difference between these two common conditions, plus what to do if you think you might have hyperthyroidism or hypothyroidism.

How the thyroid works

Close up asian man touching his neck and having sore throat.Pormezz/Shutterstock

The hormones the thyroid produces impact every single cell in the body.

“Thyroid hormone is kind of like an energy pill and is essential. It impacts every organ system—the metabolism, lungs, bones, heart and more. Think of it like oil in a car. The engine won’t run well if you have too much or too little,” says Victor J. Bernet, MD, ATA president-elect and the chair of the Division of Endocrinology at the Mayo Clinic Florida in Jacksonville.

The pituitary gland in the brain releases its own hormone, thyroid-stimulating hormone (TSH), that triggers the thyroid to pump out thyroxine (aka T4) and triiodothyronine (or T3). Both T3 and T4 help the body perform essential functions including blood circulation and temperature regulation, according to California Northstate University medical experts, and if any of those hormones are outside of their regular range levels, you might begin to notice symptoms (such as these 13 common signs of thyroid disease).

“It’s normal for the hormone levels to vary within a few points. But when the thyroid is far off from normal—the oil is very low or high on the dipstick—it’s [tougher] for your body’s engine to run, just like a car. Symptoms are more pronounced,” Dr. Bernet says.

Rates of hyperthyroidism and hypothyroidism in the U.S.

Side view portrait of attractive young woman in white bathrobe receiving ultrasound scanning of thyroidOlena Yakobchuk/Shutterstock

When comparing hyperthyroidism vs. hypothyroidism, hypo is about three times as common.

According to the latest data from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), 4.6 percent of Americans over age 12 have hypothyroidism. That translates to about one in every 20 people. Hyperthyroidism affects about one in every 100 Americans, or 1.2 percent of those over 12.

Women are much more likely to develop both conditions—and any thyroid problem—than men, per the ATA. As are those over age 60, explains Dr. Bernet, so much so that certain health task forces are considering making thyroid screening a common test after that age (similar to a mammogram or bone scan). This is not part of the recommended senior routine screening process yet, however.

Hyperthyroidism signs and symptoms

“Hyperthyroidism symptoms include heat intolerance, or you might not perceive cold. Unanticipated weight loss, feeling anxious or nervous, a racing heart, trouble falling asleep or more frequent bowel movements may also occur,” Dr. Bernet says.

Shaky hands, irritability and mood swings are also often noted in those with hyperthyroidism, according to the NIDDK.

“Unanticipated weight gain without lifestyle changes, slower pulse, drier skin, less frequent bowel movements, cold intolerance, and more tiredness are common symptoms of hypothyroidism,” Dr. Bernet says.

The NIH adds a puffy face, less sweating, and depression to the list of hypothyroidism signs.

“Fatigue, hair changes and, for women, menstrual changes may be noticed with either hyper or hypothyroidism,” Dr. Bernet adds.

You can also have subclinical hypothyroidism or hyperthyroidism, which may involve weaker, yet still noticeable, symptoms.

Risk factors for hyperthyroidism vs. hypothyroidism

Genetics play a role in thyroid conditions, including hyperthyroidism and hypothyroidism. Those who have been pregnant in the previous six months, have type 1 diabetes, or pernicious anemia (not enough red blood cells in the body) are more at-risk for both as well, the NIH reports.

“Environmental influences or previous infections may play a role, too,” Dr. Bernet says.

Some hyperthyroidism vs. hypothyroidism risk factors can vary. Hyperthyroidism can be prompted by high consumption of iodine (found in seaweed, cod and dairy products, according to the NIH). Hypothyroidism may be brought on by other thyroid issues (such as goiters or radiation to the gland, say, to treat thyroid cancer).

When to seek treatment for these thyroid conditions

Several of the common symptoms for both hyperthyroidism and hypothyroidism can be caused by other factors, so Dr. Bernet recommends vigilance.

“Track symptoms for two to four weeks before seeking medical assistance. The more symptoms, of course, the more convincing the reason to visit your doctor—you can often get answers from your primary care doctor, or if you’d prefer a specialist, see an endocrinologist,” he says.

Diagnosis of hyperthyroidism and hypothyroidism

If you think you might have thyroid issues, lab testing can be done to confirm whether you are hypo- or hyperthyroid, Der. Bernet says. Thyroid symptoms are non-specific and not unique to the thyroid, thus it’s important to eliminate other causes before beginning treatment, especially if your thyroid levels are just slightly abnormal.

Thyroid hormone production is controlled by the hypothalamic-pituitary-thyroid axis where thyroid-stimulating hormone (TSH) is released when thyroid hormone is low to stimulate thyroid cells to make more thyroid hormone (T4 and T3). That TSH can tell you about how much T3 and T4 are being produced.

“TSH is high in hypothyroidism—they have a reverse relationship. And those with overactive thyroid have a lower than usual level of TSH. Testing this works well to diagnose 99 percent of patients,” Dr. Bernet says.

All that being said, do remember that there are quite a few things standard thyroid testing can’t tell you.

“There’s no absolute cutoff in terms of lab results of TSH levels when treatment is required. It’s more of a conversation between patient and doctor. Once your doctor receives TSH lab test results, he or she will check to make sure nothing else is going on, such as a goiter or enlarged thyroid. Often, the blood test is repeated later to guarantee a firm diagnosis,” he says.

Levels of T3 and T4 can also be directly tested via a blood test.

Treatment of hyperthyroidism vs. hypothyroidism

“It’s really difficult to reverse either hyperthyroidism or hypothyroidism with food. Diet may play a role in slowing development. Sleep and exercise are important as well, but won’t fix either condition alone,” Dr. Bernet says.

Hyperthyroidism vs. hypothyroidism treatment strategies:

  • Hyper: Pharmaceutical interventions (antithyroid medicines or beta blockers), radioiodine therapy, thyroid surgery, reducing iodine consumption in the diet.

  • Hypo: Pharmaceutical interventions with levothyroxine to introduce a nearly identical hormone to those your thyroid normally makes.

The treatment method chosen is the result of a thorough conversation between doctor and patient, Dr. Bernet concludes. (Speaking of communicating with your doctor, have you asked these important questions lately?)

“By explaining the pros and cons of each, we involve patients to see what treatment option works best in their lifestyle and with their clinical picture,” Dr. Bernet says.