Symptoms of Thyroid Disorder: Hypo vs. Hyperthyroidism

What Are the Symptoms of a Thyroid Disorder?

Thyroid disorder symptoms depend on whether the thyroid is underactive (hypothyroidism) or overactive (hyperthyroidism). According to the National Institute of Diabetes and Digestive and Kidney Diseases , hypothyroidism commonly causes fatigue, weight gain, and cold intolerance, while hyperthyroidism causes weight loss, a rapid heartbeat, and heat intolerance — essentially opposite effects, since thyroid hormone controls how the body uses energy.

Both conditions are common. reports that nearly 5 out of 100 Americans age 12 and older have hypothyroidism, while about 1 out of 100 have hyperthyroidism. Women and people over age 60 are more likely to develop either condition.

Why Thyroid Symptoms Vary So Much

The thyroid is a small, butterfly-shaped gland in the neck that produces hormones controlling how the body uses energy — which is why thyroid hormone imbalances affect nearly every organ, including the heart. Too little hormone slows the body's processes down; too much speeds them up. That's the core distinction behind the very different symptom lists for each condition.

[REVIEWER: add clinical insight here — for example, which symptoms patients most commonly dismiss before eventually being diagnosed]

Symptoms of Hypothyroidism (Underactive Thyroid)

NIDDK lists these common symptoms of hypothyroidism:

• Fatigue

• Weight gain

• Trouble tolerating cold

• Joint and muscle pain

• Dry skin or dry, thinning hair

• Heavy or irregular menstrual periods, or fertility problems

• Slowed heart rate

• Depression

Because hypothyroidism develops slowly, NIDDK notes that people may not notice symptoms for months or even years. Many of these symptoms — especially fatigue and weight gain — are common on their own and don't automatically mean a thyroid problem, which is part of why diagnosis relies on blood tests rather than symptoms alone.

The most common cause of hypothyroidism is Hashimoto's disease, an autoimmune disorder in which the immune system attacks the thyroid, causing it to become inflamed and produce too little hormone. Other causes include thyroid surgery, radiation treatment, certain medications, and — rarely, in the U.S. — iodine deficiency.

Symptoms of Hyperthyroidism (Overactive Thyroid)

NIDDK lists these common symptoms of hyperthyroidism:

• Weight loss despite an increased appetite

• Rapid or irregular heartbeat

• Nervousness, irritability, trouble sleeping, fatigue

• Shaky hands, muscle weakness

• Sweating or trouble tolerating heat

• Frequent bowel movements

• An enlargement in the neck, called a goiter

The most common cause of hyperthyroidism is Graves' disease, an autoimmune disorder in which the immune system causes the thyroid to produce excess hormone. Other causes include overactive thyroid nodules, thyroiditis (inflammation of the thyroid), and consuming too much iodine.

Thyroid Symptoms Can Look Different in Older Adults

NIDDK specifically notes that in older adults, hyperthyroidism is sometimes mistaken for depression or dementia. Instead of the classic nervousness or rapid heartbeat seen in younger adults, older adults with hyperthyroidism may show loss of appetite or withdrawal from other people — subtler signs that are easy to attribute to aging or mood changes instead of a thyroid problem.

Complications If Left Untreated

Untreated hypothyroidism can contribute to high cholesterol, and NIDDK notes that severe, untreated cases can rarely progress to myxedema coma — an extreme, life-threatening slowdown of the body's functions that requires immediate medical treatment.

Untreated hyperthyroidism carries its own risks. According to NIDDK, it can lead to an irregular heartbeat that raises the risk of blood clots, stroke, and heart failure; an eye disease called Graves' ophthalmopathy; thinning bones and osteoporosis; and menstrual or fertility problems.

When to Seek Care Right Away

NIDDK advises calling a doctor immediately if you experience fatigue or weakness, dull abdominal pain, loss of appetite, skin rash or itching, easy bruising, yellowing of the skin or eyes (jaundice), or a constant sore throat or fever — particularly if you're already being treated for a thyroid condition, since these can signal a medication side effect or a worsening condition that needs prompt attention.

How Thyroid Disorders Are Diagnosed

Because thyroid symptoms overlap heavily with other conditions, NIDDK is clear that a diagnosis "can't be based on symptoms alone." A doctor will take a medical history, perform a physical exam, and order thyroid blood tests — most commonly checking thyroid-stimulating hormone (TSH) along with T4 levels — to confirm the diagnosis and identify its cause. A high TSH typically points to hypothyroidism, while a low TSH points to hyperthyroidism.

Frequently Asked Questions

What is the difference between hypothyroidism and hyperthyroidism symptoms? Hypothyroidism (underactive thyroid) tends to cause fatigue, weight gain, and cold intolerance because the body's processes slow down. Hyperthyroidism (overactive thyroid) tends to cause weight loss, rapid heartbeat, and heat intolerance because the body's processes speed up.

What are the first signs of thyroid problems? Early signs are often nonspecific, like fatigue, unexplained weight changes, or changes in heart rate. Because these overlap with many other conditions, NIDDK notes that thyroid problems can't be confirmed by symptoms alone and require blood testing.

Can thyroid problems be mistaken for depression? Yes, especially in older adults. NIDDK specifically notes that hyperthyroidism in older adults is sometimes mistaken for depression or dementia, since symptoms like withdrawal and appetite loss can look different from the classic nervousness seen in younger people.

What causes an underactive thyroid? The most common cause is Hashimoto's disease, an autoimmune condition where the immune system attacks the thyroid. Other causes include thyroid surgery, radiation treatment, certain medications, and rarely, iodine imbalance.

Is an enlarged thyroid (goiter) always a sign of hyperthyroidism? Not necessarily. A goiter can occur with an overactive thyroid, an underactive thyroid, or even normal thyroid function, so it needs to be evaluated alongside other symptoms and blood tests rather than read on its own.