There are a number of possible thyroid diseases and disorders, including thyroiditis and thyroid cancer. Two of the most common thyroid disorders are hyperthyroidism and hypothyroidism. Hyperthyroidism affects approximately 1 percent of the U.S. population, according to the National Institutes of Health (NIH). Hypothyroidism is more common and can be found in about 5 percent of Americans. While the two conditions are closely linked, they have several important differences that affect diagnosis and treatment. Here is a guide to distinguishing between hypothyroidism and hyperthyroidism.

Thyroid Basics
The thyroid is a butterfly-shaped gland in your endocrine system, which is responsible for producing and distributing the body’s hormones. Hormones regulate vital functions including body temperature, sexual function and mood. The thyroid gland makes hormones which primarily control your body’s growth and metabolism, which just means all the body processes that use energy. In short, the thyroid gland plays a huge role in breathing, blood circulation, body temperature, muscle control, digestion, bowel movements and even brain function. An issue with the thyroid gland can result in problems all over your body.

In medicine, “hypo” means deficient or not enough. For example, hypoglycemia is a term for low blood sugar. Hypothyroidism, then, is a condition in which the thyroid gland does not produce enough hormones. Inflammation and damage to the gland accounts for most cases of hypothyroidism, says the NIH. Symptoms vary from person to person, and if left untreated, they tend to worsen over time. People with hypothyroidism may feel more sensitive to temperature changes. Individuals might also experience a number of physical effects, including constipation, fatigue, weakness, joint or muscle pain and unintentional weight gain. The condition can also affect mood, causing depression or memory problems.

Hypothyroidism is typically treated with thyroid replacement therapy. Different medications can imitate and replace the role of the thyroid hormone inside the body, making up for its natural lack. This treatment usually lasts for a patient’s entire life and dosage might change over time.

While “hypo” means not enough, “hyper” indicates too much. Hyperthyroidism occurs when the thyroid gland produces an excess of hormones. The most common cause for hyperthyroidism is the autoimmune disorder Graves’ disease. Also known as an overactive thyroid, the hormone overload can cause a wide range of physical changes. Many symptoms overlap with hypothyroidism, including thinning hair, dry skin and temperature sensitivity. However, while hypothyroidism causes fatigue initially, hyperthyroidism kicks metabolism into overdrive and makes a person restless and excitable. Nonetheless, as time passes and the body stays too stimulated, tiredness will eventually take over as well. Hyperthyroidism may also cause weight loss, hair loss, high blood pressure, nausea and vomiting, nervousness and an irregular menstrual period in women.

Doctors generally treat hyperthyroidism with anti-thyroid agents. These medications prevent the thyroid from making hormones, without causing permanent damage to the thyroid gland. In some cases, surgery may be required to remove the thyroid. A person whose thyroid is removed will then enter hypothyroidism and require lifelong hormone replacement therapy.

Both hypothyroidism and hyperthyroidism can be diagnosed with thyroid function tests, which measures the levels of thyroid-stimulating hormones (TSH) in your bloodstream.