What does hypothyroidism mean?
Hypothyroidism is a medical condition in which the thyroid gland produces too little thyroid hormone or the body otherwise fails to use enough of it. The resulting reduction in thyroid hormone activity can slow metabolism and affect energy, temperature regulation, cardiovascular function, digestion, and mood. Symptoms vary and may include fatigue, weight gain, cold intolerance, constipation, and dry skin, but diagnosis depends on clinical evaluation and blood tests rather than symptoms alone. The word is used mainly in medical and public-health contexts and often appears with qualifiers such as "primary," "subclinical," or "clinical." When the cause is disease of the thyroid gland itself, the condition is called primary hypothyroidism; other causes can involve the pituitary gland or other hormonal pathways. The term is more precise than informal expressions such as "low thyroid" and should not be confused with hyperthyroidism, an opposite disorder in which thyroid hormone activity is excessive. Hypothyroidism is important because it is common, usually manageable with appropriate treatment, and can be mistaken for ordinary fatigue or depression.
nounA medical condition in which the thyroid gland produces insufficient thyroid hormone or the body does not use it effectively. It can slow metabolism and cause symptoms including fatigue, weight gain, cold intolerance, constipation, and dry skin.
- The medical condition caused by insufficient thyroid hormone activity.
"Her unexplained fatigue and weight gain were eventually diagnosed as hypothyroidism."
"Routine blood tests revealed mild subclinical hypothyroidism."
"Her endocrinologist explained that primary hypothyroidism could be treated with thyroid hormone replacement."
The plural is rare; hypothyroidism is usually treated as a mass noun or discussed through individual cases.
"The study compared primary and secondary hypothyroidisms."
An underactive thyroid can slow metabolism, energy, and even mood—a reminder that one small gland can influence systems throughout the body.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does hypothyroidism come from?
The combining element hypo- comes from Greek hypo, meaning "under," while thyroid derives from Greek thureos, meaning "shield," a reference to the shield-like thyroid cartilage. The medical suffix -ism forms a noun denoting a condition, producing hypothyroidism, literally a condition involving underactivity of the thyroid. Related terms including thyroid, thyroxine, thyrotropin, and thyrotoxicosis share the Greek root for the thyroid.
How hypothyroidism is actually used
This is a specialized medical term used chiefly in clinical, scientific, and public-health contexts. Informal paraphrases such as "low thyroid" are less precise because they do not distinguish among different causes.
Easily confused with hypothyroidism
Hypothyroidism involves insufficient thyroid hormone activity, whereas hyperthyroidism involves excessive thyroid hormone activity.