Hypothyroidism (underactive thyroid gland)

Hypothyroidism (underactive thyroid gland)
International Classification (ICD) E00.-
Symptoms Tiredness (Fatigue), Listlessness, Fatigue, Verminderte körperliche und kognitive Leistungsfähigkeit, depressive moods, Weight gain, Sensitivity to cold, Zyklusunregelmäßigkeiten, Constipation, cool/dry/doughy skin, Nail growth disorders, Hair loss, Enlargement of the thyroid gland (goiter or goiter)
Possible causes Autoimmune disease, Medication, Operations, Trace elements deficiency, Disruption of the hormonal regulatory circuits, Congenital malformation


In hypothyroidism, there is a deficiency of the thyroid hormones triiodothyronine and thyroxine in the body.

Graphic representation of the goiter Kropf (Struma) bei einer Schilddrüsenunterfunktion (Servier Medical Art by Servier / Creative Commons Attribution 3.0 unported license)

For various reasons, there is a reduced or completely restricted hormone production by the thyroid gland and subsequent deficiency of thyroid hormones, which the body needs to maintain its metabolic processes. A common feature is a visibly enlarged thyroid gland (called goiter or goiter). The consequences of hypothyroidism are metabolic restrictions and symptoms such as fatigue and exhaustion. Hypothyroidism in infancy and childhood can lead to growth and developmental disorders.


In most cases, there is acquired primary hypothyroidism, in which thyroid function is normal at the time of birth and symptoms develop later in life. Primary means that hormone production is disturbed directly in the thyroid gland. Possible causes are:

Hashimoto's thyroiditis

The most common cause of hypothyroidism is Hashimoto's thyroiditis. In the course of this autoimmune disease, autoantibodies are formed against components of the thyroid cells for reasons that are still unknown. The triggered chronic inflammation leads to damage of the thyroid gland with a decrease in hormone production.

Medically triggered (iatrogenic)

In some cases, hypothyroidism exists because of a medical act. This may be intentional or unintentional. Examples include surgery in which all or part of the thyroid gland has been removed. Also, taking anti-thyroid drugs (thyrostatic drugs) or the side effect of other drugs (including amiodarone) can be causative for hypothyroidism.

Deficiency of trace elements

A pronounced deficiency of iodine or selenium can lead to hypothyroidism.

Secondary or tertiary hypothyroidism

In rare cases, hypothyroidism is the result of a problem in the upstream hormonal regulatory circuits in the pituitary gland (hypophysis) or in the brain (hypothalamus). This is referred to as secondary or tertiary hypothyroidism.

Congenital hypothyroidism

Rarely, there is also a congenital form in which, for example, a missing or only partially attached thyroid gland or receptor defects are responsible for the hypothyroidism.


A deficiency of thyroid hormones affects most organs of the human body. Patients with hypothyroidism usually feel powerless and tired. The thyroid gland tries to compensate for the reduced hormone production with increased growth, which is why people with hypothyroidism are often diagnosed with thyroid enlargement (goiter).

The following signs of illness are indicative of hypothyroidism:

  • tiredness (fatigue) and weakness
  • listlessness
  • Fatigue
  • Decreased physical and cognitive performance
  • Depressive moods, sadness
  • Weight gain (sometimes despite changes in dietary habits)
  • Excessive sensitivity to cold
  • Irregular menstrual cycles and, as a consequence, possibly reduced fertility
  • Constipation (constipation)
  • Cool, dry and/or doughy skin
  • Disturbances in nail growth
  • Hair loss (effluvium)

Especially in older patients, symptoms are often nonspecific, making diagnosis of hypothyroidism difficult.

Newborns with hypothyroidism are often conspicuous by reduced drinking behavior, digestive disturbances and lower locomotor activity. Hypothyroidism negatively affects development and growth in children, which is why children with hypothyroidism may show delayed mental and physical development.


In order to diagnose a thyroid disease or dysfunction, the thyroid function (over-, under- or normal function) is determined by blood test and the thyroid structure (morphology) is examined by ultrasound after a detailed interview including a medical history. These two parameters do not necessarily correlate and must always be considered in combination in order to finally arrive at a diagnosis and subsequently adequate therapy.

Examination of thyroid function

The healthy function of the thyroid gland is based on the following mechanism: The thyroid gland secretes the free thyroid hormones thyroxine (fT4) and a small amount of triiodothyronine (fT3), which are essential for metabolism. fT3 is also converted from fT4 outside the thyroid gland in various organs and made available to the body.

Thyroid hormones T3 and T4 Hormone der Schilddrüse T3 und T4 (Dr_Microbe / iStock)

The level of fT4 and fT3 in the blood is in turn regulated by the pituitary gland in the brain, which produces TSH. TSH is considered the most sensitive parameter with regard to a possible thyroid dysfunction: a rising TSH level is the first sign of hypothyroidism; a falling TSH level, on the other hand, is the first sign of hyperthyroidism. The pituitary gland performs a function similar to that of a thermostat in a heating system: it detects even the slightest deviations in the thyroid hormones fT4 and fT3 and adjusts the release of TSH accordingly. If the thyroid hormone level in the blood is too low, the pituitary gland secretes larger amounts of TSH; if the thyroid hormone level in the blood is too high, the pituitary gland causes TSH to drop. Accordingly, continuously high TSH levels provide the physician with evidence of hypothyroidism.

The examination of thyroid function is carried out by means of blood sampling. Antibodies directed against the thyroid gland can also be tested.

Babies are routinely screened for the presence of hypothyroidism after birth during newborn screening. For this test, a few drops of blood are taken from the newborn's foot on the third day after birth and analyzed.

Examination of the thyroid structure (morphology)


The structure of the thyroid tissue also provides information about the function or condition of the thyroid gland. Ultrasound examination can be used to determine the size, texture and presence or degree of inflammatory infiltration of the thyroid tissue.

Thyroid scintigraphy

Another examination and diagnostic method is thyroid scintigraphy. In this nuclear medicine examination, a mildly radioactive drug is administered to the patient either intravenously or orally. The patient must then wait about 20 minutes so that the drug - just like naturally occurring iodine - can accumulate in the thyroid gland. This allows the regional metabolism of the thyroid gland to be recorded using a gamma camera. The slightly radioactive drug is harmless; the patient excretes it in the urine within a day. Thyroid scintigraphy is used in the case of hypothyroidism to investigate the cause and differentiate it from other diseases.


In the rare cases where there is a specific cause for hypothyroidism, it should be treated, for example, by discontinuing causative medications (thyrostatic agents, amiodarone) or compensating for iodine deficiency.

Hypothyroidism can usually be treated very well with hormone replacement therapy. The aim of treatment is to compensate for the hypothyroidism by means of thyroid hormone in the form of tablets, so that the symptoms caused by it disappear. The thyroid hormone that the thyroid gland can no longer produce on its own is therefore permanently replaced by a hormone tablet (hormone replacement). The daily intake of thyroid hormone tablets is usually necessary for patients with hypothyroidism for the rest of their lives. Regular checks and, if necessary, adjustments of the medication dose - especially in special phases of life such as during childbearing, pregnancy and breastfeeding - are extremely important.

Treatment is started with a low dosage and slowly increased until the desired dose of effect is achieved.

Timely treatment with thyroid hormones is also important for newborns and children with congenital hypothyroidism in order to prevent possible developmental disorders and to enable healthy development.


Hypothyroidism has a good prognosis in most cases, since it can be treated adequately with hormone preparations. Existing symptoms such as fatigue and reduced performance usually subside under substitution.

Newborns with hypothyroidism have a good chance of normal development if the disease is recognized and treated early. However, if hypothyroidism is detected too late, growth and developmental disorders can no longer be reversed.


In most cases, hypothyroidism is caused by Hashimoto's thyroiditis, against whose autoimmune reaction no preventive measures exist.

Hypothyroidism caused by iodine deficiency can be prevented by sufficient iodine intake. In German-speaking countries, iodine is added to conventional table salt to ensure an adequate supply.

If there are indications of hypothyroidism, the patient should be seen by a doctor and checked.


  • Herold, G. (2023). Innere Medizin. Gerd Herold Verlag. Köln.

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All information used for the content comes from verified sources (recognised institutions, experts, studies by renowned universities). We attach great importance to the qualification of the authors and the scientific background of the information. Thus, we ensure that our research is based on scientific findings.
Danilo Glisic

Danilo Glisic

As a biology and mathematics student, he is passionate about writing magazine articles on current medical topics. Due to his affinity for facts, figures and data, his focus is on describing relevant clinical trial results.

Dr. med. univ. Bernhard Peuker, MSc

Dr. med. univ. Bernhard Peuker, MSc

Bernhard Peuker is a lecturer and medical advisor at Medikamio and works as a physician in Vienna. In his work, he incorporates his clinical knowledge, practical experience and scientific passion.

The content of this page is an automated and high-quality translation from DeepL. You can find the original content in German here.



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