Hyperthyroidism | Definition, Causes, Symptoms, & Treatment

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class="md-content"> <div class="md-article-container template-desktop"> <div class="infinite-scroll-container article last"> <article class="article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded" data-topic-id="279737"> <div class="grid gx-0"> <div class="col-auto"> <div class="topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/science/hyperthyroidism">hyperthyroidism</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/science/hyperthyroidism">Introduction</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref285772"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/hyperthyroidism#ref285772">Causes of hyperthyroidism</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref285773"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/hyperthyroidism#ref285773">Symptoms of hyperthyroidism</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref285774"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/hyperthyroidism#ref285774">Diagnosis of hyperthyroidism</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref285775"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/hyperthyroidism#ref285775">Treatment of hyperthyroidism</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/science/hyperthyroidism/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/hyperthyroidism">Quick Facts & Related Topics</a> </div> <div class="mb-30 tlr-related-quizzes"> <div class="text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10"> Quizzes </div> <div 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Utiger</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Clinical Professor of Medicine, Harvard Medical School.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Robert D. Utiger</span></div> <div class="font-serif font-12 text-gray-700"> <span class="qa-fact-checked-by">Fact-checked by</span> <div class="editor-popover popover p-0"> <a class="d-block p-20 font-12" href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419" > <div class="editor-title font-16 font-weight-bold">The Editors of Encyclopaedia Britannica</div> <div class="editor-description font-12 font-serif mt-5 text-black">Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <span class="text-gray-700"> Last Updated: <time datetime="2024-11-19T00:00:00CST" >Nov 19, 2024</time> •</span> <a class="byline-edit-history" href="https://www.britannica.com/science/hyperthyroidism/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn border-2 ai-ask-button btn border-2 module-spacing btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400 p-10 ml-5"> Ask the Chatbot a Question </button> </div> <div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Also called: </dt> <dd>thyrotoxicosis</dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Related Topics: </dt> <dd><a href="/science/metabolic-disease" topicid="377311">metabolic disease</a></dd> <dd><a href="/science/thyroid-gland" topicid="594629">thyroid gland</a></dd> <dd><a href="/science/Graves-disease" topicid="242366">Graves disease</a></dd> <dd><a href="/science/thyroid-hormone" topicid="594672">thyroid hormone</a></dd> <dd><a href="/topic/thyroid-storm" topicid="594622">thyroid storm</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/hyperthyroidism"> See all related content </a> </div> </div> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref115589"></span>hyperthyroidism</strong>, excess production of <span id="ref115590"></span><a href="https://www.britannica.com/science/thyroid-hormone" class="md-crosslink ">thyroid hormone</a> by the <a href="https://www.britannica.com/science/thyroid-gland" class="md-crosslink " data-show-preview="true">thyroid gland</a>. Most patients with hyperthyroidism have an enlarged thyroid gland (<span id="ref115591"></span><a href="https://www.britannica.com/science/goitre" class="md-crosslink " data-show-preview="true">goitre</a>), but the <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="characteristics" href="https://www.britannica.com/dictionary/characteristics" data-type="EB">characteristics</a> of the enlargement vary. Examples of thyroid disorders that give rise to hyperthyroidism include diffuse goitre (<span id="ref115592"></span><a href="https://www.britannica.com/science/Graves-disease" class="md-crosslink " data-show-preview="true">Graves disease</a>), toxic multinodular goitre (<span id="ref1113729"></span><a href="https://www.britannica.com/science/Plummer-disease" class="md-crosslink " data-show-preview="true">Plummer disease</a>), and thyroid <a href="https://www.britannica.com/science/inflammation" class="md-crosslink autoxref " data-show-preview="true">inflammation</a> (<span id="ref934641"></span><a href="https://www.britannica.com/science/thyroiditis" class="md-crosslink " data-show-preview="true">thyroiditis</a>). Hyperthyroidism occurs more often in adults than in children, and it is 5 to 10 times more common in women than in men.</p><span class="marker MOD1 mod-inline"></span></section> <span class="marker h2"></span><section data-level="1" id="ref285772"><h2 class="h1">Causes of hyperthyroidism</h2> <span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">The most common cause of hyperthyroidism is Graves disease, named for the Irish physician <span id="ref1270855"></span><a href="https://www.britannica.com/biography/Robert-James-Graves" class="md-crosslink " data-show-preview="true">Robert Graves</a>, who was among the first to describe the condition. Graves disease is an <a href="https://www.britannica.com/science/autoimmunity" class="md-crosslink " data-show-preview="true">autoimmune</a> disorder in which hyperthyroidism and goitre are caused by thyroid-stimulating <a href="https://www.britannica.com/science/antibody" class="md-crosslink " data-show-preview="true">antibodies</a>. These antibodies bind to and activate <a href="https://www.britannica.com/science/thyrotropin" class="md-crosslink " data-show-preview="true">thyrotropin</a> (thyroid-stimulating hormone; TSH) <a href="https://www.britannica.com/science/receptor-nerve-ending" class="md-crosslink " data-show-preview="true">receptors</a> on the thyroid gland, thereby mimicking the actions of thyrotropin. Risk factors for Graves disease include gender (women are affected more often than men), <a href="https://www.britannica.com/topic/smoking-tobacco" class="md-crosslink " data-show-preview="true">smoking</a>, and a high intake of <a href="https://www.britannica.com/science/iodine" class="md-crosslink " data-show-preview="true">iodine</a>. In addition, some individuals possess genetic susceptibility to the <a href="https://www.britannica.com/science/disease" class="md-crosslink autoxref " data-show-preview="true">disease</a>. The immediate events that lead to the production of thyroid-stimulating antibodies that cause hyperthyroidism are not known, although emotional <a href="https://www.britannica.com/science/stress-psychology-and-biology" class="md-crosslink " data-show-preview="true">stress</a> has been <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="postulated" href="https://www.britannica.com/dictionary/postulated" data-type="EB">postulated</a> to be an important factor. An interesting feature of Graves disease is spontaneous remission, with a disappearance of the thyroid-stimulating antibodies. In these patients, antithyroid drug treatment can be withdrawn without recurrence of hyperthyroidism.</p><span class="marker MOD2 mod-inline"></span> <span class="marker PREMOD3 mod-inline"></span><p class="topic-paragraph">Approximately 25 to 35 percent of patients with Graves disease have <span id="ref956798"></span><a href="https://www.britannica.com/science/Graves-ophthalmopathy" class="md-crosslink ">Graves ophthalmopathy</a>. The defining characteristic of this condition is the protrusion of the eyes (<a href="https://www.britannica.com/science/exophthalmos" class="md-crosslink " data-show-preview="true">exophthalmos</a>). The eyelids may be retracted upward, making it seem as though the person is constantly staring. The tissues surrounding the eyes may swell, and the eye muscles may not function properly, causing <a href="https://www.britannica.com/science/double-vision-physiology" class="md-crosslink " data-show-preview="true">double vision</a>. In rare cases, vision is decreased because of compression or stretching of the <a href="https://www.britannica.com/science/optic-nerve" class="md-crosslink " data-show-preview="true">optic nerve</a>. These changes are caused by <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="swelling" href="https://www.britannica.com/dictionary/swelling" data-type="EB">swelling</a> and inflammation of the eye muscles and the <a href="https://www.britannica.com/science/adipose-cell" class="md-crosslink " data-show-preview="true">adipose</a> (fat) tissue behind the eyes. Approximately 1 to 2 percent of patients with Graves disease have localized <span id="ref1270856"></span><a href="https://www.britannica.com/science/myxedema" class="md-crosslink " data-show-preview="true">myxedema</a>, which is characterized by circumscribed thickening of the skin and subcutaneous tissue on the lower legs (pretibial myxedema), arms, or trunk. Nearly all patients with localized myxedema have severe ophthalmopathy and have had hyperthyroidism in the past. Ophthalmopathy and localized myxedema are believed to be caused by both antibody-mediated and cell-mediated immunologic mechanisms. Whether the antibodies are thyroid-stimulating antibodies or different antibodies is not known.</p><a class="link-module shadow-sm d-block qa-quiz-module" href="/quiz/a-visit-with-the-word-doctor-medical-vocabulary-quiz" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/28/254328-131-8CF54640/Yorkshire-terrier-dressed-as-doctor.jpg" alt="A Yorkshire terrier dressed up as a veterinarian or doctor on a white background. (dogs)" class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-green">Britannica Quiz</div> <div class="font-weight-semi-bold mt-5">A Visit with the Word Doctor: Medical Vocabulary Quiz</div> </div> </a><span class="marker MOD3 mod-inline"></span> <span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">The second most common cause of hyperthyroidism is <span id="ref307839"></span><a href="https://www.britannica.com/science/Plummer-disease" class="md-crosslink " data-show-preview="true">toxic multinodular goitre</a>, or Plummer disease. This condition begins early in life and is due to <a href="https://www.britannica.com/science/iodine-deficiency" class="md-crosslink " data-show-preview="true">iodine deficiency</a> or to other factors that decrease thyroid hormone secretion and result in a persistent increase in thyrotropin secretion and therefore persistent thyroid gland stimulation. This stimulation initially causes generalized thyroid enlargement, but, as time passes, localized regions of the gland grow and function independently of thyrotropin. A less common cause of hyperthyroidism is a <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="benign" href="https://www.merriam-webster.com/dictionary/benign" data-type="MW">benign</a> <a href="https://www.britannica.com/science/tumor" class="md-crosslink " data-show-preview="true">tumour</a> (toxic adenoma) of the thyroid gland. In many cases these tumours contain a <a href="https://www.britannica.com/science/mutation-genetics" class="md-crosslink " data-show-preview="true">mutation</a> of the thyrotropin receptor <a href="https://www.britannica.com/science/gene" class="md-crosslink " data-show-preview="true">gene</a> that results in the synthesis of thyrotropin receptors that are active and therefore lead to excess thyroid hormone production in the absence of thyrotropin.</p><span class="marker MOD4 mod-inline"></span> <span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph">Several types of <span id="ref956799"></span><a href="https://www.britannica.com/science/thyroiditis" class="md-crosslink " data-show-preview="true">thyroiditis</a> can result in the release of stored thyroid hormone in amounts sufficient to cause hyperthyroidism. One type, called silent lymphocytic thyroiditis, is painless and is particularly common in women in the first year after a <a href="https://www.britannica.com/science/pregnancy" class="md-crosslink " data-show-preview="true">pregnancy</a> (postpartum thyroiditis). Another type, called subacute <a href="https://www.britannica.com/science/granulomatous-thyroiditis" class="md-crosslink autoxref " data-show-preview="true">granulomatous thyroiditis</a>, is characterized by thyroid pain and tenderness. Hyperthyroidism in patients with thyroiditis is usually mild and self-limiting, lasting only until the stores of hormone in the thyroid gland are exhausted.</p><span class="marker MOD5 mod-inline"></span> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">The administration of high doses of thyroid hormone is a common cause of hyperthyroidism. The hormone may have been given by a physician to treat hypothyroidism or to decrease the size of a goitre. In addition, some patients purchase thyroid hormone from <a href="https://www.britannica.com/topic/health" class="md-crosslink autoxref " data-show-preview="true">health</a> and nutrition stores in the form of a crude thyroid extract or an <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="analogue" href="https://www.merriam-webster.com/dictionary/analogue" data-type="MW">analogue</a> of thyroid hormone purported to stimulate metabolism and cause weight loss. These preparations may contain variable amounts of thyroid hormone and can have unpredictable effects on the body.</p><span class="marker MOD6 mod-inline"></span> <span class="marker PREMOD7 mod-inline"></span><p class="topic-paragraph">In rare cases, hyperthyroidism may be caused by a thyrotropin-secreting tumour of the <a href="https://www.britannica.com/science/pituitary-gland" class="md-crosslink " data-show-preview="true">pituitary gland</a> or a struma ovarii, in which hyperfunctioning thyroid tissue is present in a tumour of the <a href="https://www.britannica.com/science/ovary-animal-and-human" class="md-crosslink " data-show-preview="true">ovary</a>.</p><div class="module-spacing"> <DIV class="marketing-INLINE_SUBSCRIPTION marketing-content" data-marketing-id="INLINE_SUBSCRIPTION"><style> .student-promo-banner-wrapper { container-type: inline-size; margin-bottom: 15px; } @container (min-width: 475px) { .student-promo-banner { flex-direction: row; } .student-promo-banner-img-wrapper { margin-bottom: 0; margin-right: 10px; justify-content: flex-start; } .student-promo-banner-text-wrapper { text-align: left; margin-bottom: 0px; margin-left: 10px; } .student-promo-banner-button-wrapper { margin-right: 0; } }</style> <div class="student-promo-banner-wrapper"> <div class="student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20"> <div class="student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center"> <img class="rounded" style="max-width: 100px; min-width: 80px" src="https://cdn.britannica.com/marketing/BlueThistle.webp" /> </div> <div class="student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white"> <div class="h2 mb-10">Get Unlimited Access</div> <div class="h4 font-weight-semi-bold">Try Britannica Premium for free and discover more.</div> </div> <div class="student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto"> <a class="btn btn-m btn-orange" href="https://premium.britannica.com/premium-membership/?utm_source=premium&utm_medium=inline-cta&utm_campaign=black-friday-2024">Subscribe</a> </div> </div> </div> </DIV></div><span class="marker MOD7 mod-inline"></span></section> <span class="marker h3"></span><section data-level="1" id="ref285773"><h2 class="h1">Symptoms of hyperthyroidism</h2> <span class="marker PREMOD8 mod-inline"></span><p class="topic-paragraph">The onset of hyperthyroidism is usually gradual but can be sudden. The increase in thyroid hormone secretion results in an increase in the function of many organ systems. The cardiovascular and neuromuscular systems are likely to be affected. The cardiovascular <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="symptoms" href="https://www.britannica.com/dictionary/symptoms" data-type="EB">symptoms</a> and signs of hyperthyroidism include an increase in <a href="https://www.britannica.com/science/heart-rate" class="md-crosslink autoxref " data-show-preview="true">heart rate</a> (<a href="https://www.britannica.com/science/tachycardia" class="md-crosslink " data-show-preview="true">tachycardia</a>), <a href="https://www.britannica.com/science/atrial-fibrillation" class="md-crosslink " data-show-preview="true">atrial fibrillation</a> (rapid irregular heart rhythm), palpitations (pounding in the chest due to forceful contraction of the heart), shortness of breath, and exercise intolerance. Neuromuscular symptoms and signs of hyperthyroidism include nervousness, hyperactivity and restlessness, <a href="https://www.britannica.com/science/anxiety" class="md-crosslink " data-show-preview="true">anxiety</a> and irritability, <a href="https://www.britannica.com/science/insomnia" class="md-crosslink " data-show-preview="true">insomnia</a>, tremor, and muscle weakness. Other common symptoms and signs of hyperthyroidism are weight loss despite a good or even increased <a href="https://www.britannica.com/science/appetite" class="md-crosslink " data-show-preview="true">appetite</a>, increased <a href="https://www.britannica.com/science/perspiration" class="md-crosslink " data-show-preview="true">perspiration</a> and intolerance of <a href="https://www.britannica.com/science/heat" class="md-crosslink autoxref " data-show-preview="true">heat</a>, increased frequency of bowel movements, and irregular menstrual cycles and decreased menstrual blood flow in women. Hyperthyroidism also causes an increase in <a href="https://www.britannica.com/science/bone-anatomy" class="md-crosslink " data-show-preview="true">bone</a> resorption and therefore contributes to <a href="https://www.britannica.com/science/osteoporosis" class="md-crosslink " data-show-preview="true">osteoporosis</a>. The most severe form of hyperthyroidism is <span id="ref934642"></span>thyroid storm. This <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="acute" href="https://www.merriam-webster.com/dictionary/acute" data-type="MW">acute</a> condition is characterized by very rapid heart rate, <a href="https://www.britannica.com/science/fever" class="md-crosslink " data-show-preview="true">fever</a>, <a href="https://www.britannica.com/science/hypertension" class="md-crosslink " data-show-preview="true">hypertension</a> (high blood pressure), and certain gastrointestinal and neurological symptoms and may result in <a href="https://www.britannica.com/science/heart-failure" class="md-crosslink " data-show-preview="true">heart failure</a>, <a href="https://www.britannica.com/science/hypotension" class="md-crosslink " data-show-preview="true">hypotension</a> (low blood pressure), <a href="https://www.britannica.com/science/shock-physiology" class="md-crosslink " data-show-preview="true">shock</a>, and death.</p><span class="marker MOD8 mod-inline"></span></section> <span class="marker h4"></span><section data-level="1" id="ref285774"><h2 class="h1">Diagnosis of hyperthyroidism</h2> <span class="marker PREMOD9 mod-inline"></span><p class="topic-paragraph">Hyperthyroidism is diagnosed based on the symptoms and signs described above and on measurements of high serum total and free thyroid hormone concentrations and low, sometimes undetectable, serum thyrotropin concentrations. In serum, there are actually two thyroid hormones, <span id="ref934644"></span><a href="https://www.britannica.com/science/thyroxine" class="md-crosslink " data-show-preview="true">thyroxine</a> and <span id="ref1270857"></span><a href="https://www.britannica.com/science/triiodothyronine" class="md-crosslink ">triiodothyronine</a>, with the former being produced in much greater quantities than the latter. Thyroid hormones exist in two forms, one of which is bound to several proteins, and the other of which, a very small amount, is free. Thus, <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="serum" href="https://www.britannica.com/dictionary/serum" data-type="EB">serum</a> thyroxine can be measured as <span id="ref934648"></span>serum total thyroxine or <span id="ref934653"></span>free thyroxine; the latter is preferable because it is the form of thyroxine that is readily available to the cells of the body and, therefore, is metabolically active. Measurements of serum total thyroxine are high in patients with thyroid disease and in patients producing more of the proteins that bind to thyroxine.</p><span class="marker MOD9 mod-inline"></span> <span class="marker PREMOD10 mod-inline"></span><p class="topic-paragraph">The cause of hyperthyroidism may be distinguished based on relative differences in the concentrations of thyroxine, triiodothyronine, and thyrotropin. Patients with a thyrotropin-secreting <a href="https://www.britannica.com/science/pituitary-tumor" class="md-crosslink " data-show-preview="true">pituitary tumour</a> have normal or high serum thyrotropin concentrations. Rarely, patients have normal serum thyroxine concentrations but high serum triiodothyronine concentrations. These patients are said to have triiodothyronine thyrotoxicosis. Other patients have low serum thyrotropin concentrations but normal serum thyroxine and triiodothyronine concentrations, with few or no symptoms and signs of hyperthyroidism. These patients are said to have subclinical hyperthyroidism. Thyroid uptake of radioiodine may be measured to distinguish thyroiditis or excess thyroid hormone administration, in which the thyroid uptake is low, from other causes of hyperthyroidism, in which the thyroid uptake is high.</p><div class="one-good-fact-module"> </div><span class="marker MOD10 mod-inline"></span></section> <span class="marker h5"></span><section data-level="1" id="ref285775"><h2 class="h1">Treatment of hyperthyroidism</h2> <span class="marker PREMOD11 mod-inline"></span><p class="topic-paragraph">Hyperthyroidism is usually a chronic, even lifelong, disorder. It can be treated with an antithyroid drug, radioactive <a href="https://www.britannica.com/science/iodine" class="md-crosslink " data-show-preview="true">iodine</a>, or <a href="https://www.britannica.com/science/surgery-medicine" class="md-crosslink autoxref " data-show-preview="true">surgery</a> (thyroidectomy), in which a portion or all of the thyroid gland is surgically removed. There are three widely used antithyroid drugs—<span id="ref934656"></span>methimazole, <span id="ref934657"></span>carbimazole (which is rapidly converted to methimazole in the body), and <span id="ref934661"></span>propylthiouracil. These drugs block the production of thyroid hormone but have no permanent effect on either the thyroid gland or the <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="underlying" href="https://www.britannica.com/dictionary/underlying" data-type="EB">underlying</a> cause of the hyperthyroidism. Patients with hyperthyroidism caused by Graves disease are often <span id="ref934663"></span><a href="https://www.britannica.com/science/therapeutics" class="md-crosslink " data-show-preview="true">treated</a> with an antithyroid drug for one to two years in the hope that they will have a remission of the disease and remain well after the drug is stopped; this is successful in 30 to 50 percent of patients. Radioactive iodine is taken up by thyroid <a href="https://www.britannica.com/science/cell-biology" class="md-crosslink " data-show-preview="true">cell</a>s in the same way as is nonradioactive iodine, but the radiation destroys the cells, thereby reducing thyroid hormone production and also reducing the size of the thyroid gland. It is highly effective, but it results ultimately in <span id="ref934664"></span><a href="https://www.britannica.com/science/hypothyroidism" class="md-crosslink " data-show-preview="true">hypothyroidism</a> in most patients and, in some patients, may even lead to the later development of certain types of solid <a href="https://www.britannica.com/science/cancer-disease" class="md-crosslink " data-show-preview="true">cancers</a> (e.g., <a href="https://www.britannica.com/science/breast-cancer" class="md-crosslink " data-show-preview="true">breast cancer</a>). It is suitable for patients with Graves disease and is the preferred treatment for patients with a nodular goitre, in whom hyperthyroidism is a lifelong condition. The removal of the thyroid by thyroidectomy is rarely performed, except in the case of patients with a large goitre. When caused by thyroiditis, hyperthyroidism is <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="transient" href="https://www.merriam-webster.com/dictionary/transient" data-type="MW">transient</a>, usually lasting only four to six weeks or at most two months. Most patients need no treatment or only symptomatic treatment with a beta-<a href="https://www.britannica.com/science/adrenergic-drug" class="md-crosslink " data-show-preview="true">adrenergic</a> <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="antagonist" href="https://www.merriam-webster.com/dictionary/antagonist" data-type="MW">antagonist</a> drug (<a href="https://www.britannica.com/science/beta-blocker" class="md-crosslink " data-show-preview="true">beta-blocker</a>).</p><span class="marker MOD11 mod-inline"></span><span class="md-signature"><a href="/contributor/Robert-D-Utiger/5940">Robert D. 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Hyperthyroidism | Definition, Causes, Symptoms, & Treatment | Britannica