Underactive thyroid (hypothyroidism)

At a glance

  • An underactive thyroid is where the thyroid gland doesn’t make enough hormones.
  • This can lead to problems such as tiredness, changes in the skin and feeling down.
  • Treatment with hormone tablets usually makes the symptoms go away.
  • An underactive thyroid typically occurs in adults, and is more common in women than in men.
  • It is most often caused by an inflammation of the thyroid gland.


Photo of a woman reading

The thyroid gland makes hormones that control many of the processes in our body. The thyroid is said to be underactive if it doesn't produce enough . This condition is also referred to as hypothyroidism. It can lead to various problems, such as tiredness, lethargy, changes in the skin, and constipation.

Chronic of the thyroid gland (Hashimoto's disease) is the most common cause of an underactive thyroid. The problem can be corrected by taking tablets containing thyroid every day. This usually makes the symptoms go away.

An overactive thyroid (hyperthyroidism) occurs if the thyroid gland makes too many .


If the thyroid doesn't produce enough , your metabolism (a set of chemical reactions in the body) slows down. That can affect various body functions and cause a number of different symptoms. For example, a reduction in physical fitness. Symptoms of this might include:

  • Weakness and tiredness
  • Low pulse
  • Shortness of breath

Mental health or cognitive problems are also possible. For instance:

  • Problems with concentration or memory
  • Lethargy
  • Depression or other psychological problems

It can lead to physical changes too, such as:

Other symptoms may affect your entire body, like:

  • Sensitivity to cold, chills
  • Muscle or joint pain
  • Tingling or numbness
  • Slow reflexes
Illustration: Possible symptoms of an underactive thyroid gland


There are various reasons why the thyroid gland might not produce enough :

  • Inflammation of the thyroid gland: The organ may become inflamed due to an autoimmune reaction. This is known as Hashimoto's disease (or Hashimoto’s thyroiditis). It is the most common cause of an underactive thyroid in Germany and other countries. The may be caused by an instead. Sometimes no clear cause is found.
  • Thyroidectomy or radiation therapy: Sometimes treatment for an overactive thyroid gland or thyroid cancer involves using radioactive iodine (radioiodine) on the thyroid gland, or surgically removing part or all of the gland (thyroidectomy). As a result, not enough thyroid are made, or none are made at all.
  • Severe iodine deficiency: The body needs the trace element iodine in order to produce thyroid . Eating a balanced diet and using iodized salt can help make sure you get enough iodine. Iodine-rich foods include seafood, milk, dairy products and eggs.
  • Medications: An underactive thyroid can also be caused by medication, for example as a side effect of an antidepressant that contains lithium. Other medications may be used especially to reduce the production of thyroid in people who have an overactive thyroid. If the dose is too high, the thyroid might become underactive.
  • Congenital (“at birth”) hypothyroidism: People are only rarely born with an underactive thyroid because of their genes. It can also develop if a pregnant woman doesn't get enough iodine or if her makes antibodies against the thyroid tissue.

In all of these forms, the thyroid gland itself no longer works properly. Doctors call this "primary hypothyroidism." Only very rarely is hypothyroidism caused by a problem with the pituitary gland or hypothalamus in the brain. These organs regulate the production of in the thyroid gland. If they aren't working properly, the thyroid gland won't produce enough even if it's healthy. This is called central hypothyroidism.


About 5 out of 100 people have an underactive thyroid in countries like Germany. It is especially common in women and in older age. About 1 out of 3,400 babies are born with an underactive thyroid.


How an underactive thyroid develops over time will depend on what's causing it. It often develops slowly because it is very commonly caused by an of the thyroid gland. This usually leads to the gradual loss of thyroid tissue, which can go unnoticed for a long time: The remaining tissue makes up for this by producing more . But symptoms arise when that is no longer possible. If an underactive thyroid isn't treated, various problems can develop.

Sometimes the thyroid gets better on its own, though – for instance, if the goes away.


Complications can arise over the long term if an underactive thyroid isn't treated. The effects can be serious, especially in children. Some are permanent – such as dwarfism (short height), partial or full loss of hearing, and problems with mental and cognitive development. This is very rare in Germany and other industrialized countries though, because it's usually detected in newborn check-ups () shortly after birth and then treated in time.

If an underactive thyroid is left untreated in adults, complications such as cardiovascular (heart and blood vessel) disease, confusion and drowsiness are possible. In very rare cases it can lead to a coma.


Your doctor will ask about your symptoms and examine the thyroid by feeling your neck. Because many of the symptoms of an underactive thyroid could have other causes, blood tests are done to get a clear .

The tests measure the levels of various in your blood. These include the thyroid themselves. But another hormone called TSH (thyroid-stimulating hormone) is important too. It is produced in the pituitary gland, not in the thyroid. As its name suggests, TSH stimulates the thyroid gland to produce thyroid .

A higher level of TSH in your blood may be a sign of an underactive thyroid. This is because as soon as the thyroid gland gets weaker, the pituitary gland responds: It increases the amount of TSH it makes in order to stimulate the thyroid to make more thyroid . But this is not enough if the thyroid is very underactive: The thyroid still can't release enough into the bloodstream. This can also be seen in a blood test.

Good to know:

An underactive thyroid and other thyroid conditions can be diagnosed using various tests. They are all explained briefly in the “Understanding thyroid tests” information.


Newborns are routinely screened for high TSH levels in order to detect an underactive thyroid early on so that it can be treated sooner. If the results are abnormal, doctors also measure the level of thyroid .

Screening is not recommended in adults because abnormal TSH levels don't automatically mean that the thyroid isn't producing enough and causing problems. What's more, TSH levels that are just a little high very often go down on their own, but it can sometimes take a while. So abnormal levels could lead to unnecessary further testing, treatments and worry.

If your TSH is high but your thyroid gland is still making enough and you don't have any symptoms, it's known as subclinical (latent) hypothyroidism.

Each year in Germany, 2 to 5 out of 100 people who have subclinical hypothyroidism develop an underactive thyroid with symptoms. It's not clear whether this can be prevented with early treatment, though.


You can't prevent a thyroid gland from becoming underactive – with one exception: An underactive thyroid caused by iodine deficiency can be prevented by getting enough iodine. Experts recommend that you make sure that you get enough iodine in your diet. You can do this by having milk, dairy products or eggs on a daily basis and eating saltwater fish regularly. The use of iodized table salt is also recommended.

Some dietary supplements have iodine in them too. Taking them on a daily basis can cause problems if the supplements contain more than 100 µg (micrograms) of iodine. If you take too much iodine over the long term, it increases your risk of developing an overactive thyroid. It is almost impossible to get too much iodine from food and drink, though. One exception is dried algae, especially seaweed and kelp.


If the levels of thyroxine (a thyroid hormone made in the body) are too low, a medication that is transformed into the hormone inside the body is used to replace it. This medication is called levothyroxine or L-thyroxine. It keeps hormone levels within the normal range, and the symptoms typically go away completely. It takes about two to three months for the body's hormone levels to return to normal. Depending on the cause, treatment for an underactive thyroid may be temporary or lifelong.

The main thing to know is that

L-thyroxine is taken as a tablet once a day. Doctors recommend taking the tablet with a glass of water half an hour before breakfast.

Taken at the right dose, side effects are very rare. The dose is determined based on the person’s body weight. If the dose is too high, it can cause agitation. So the dose is checked regularly during the first few weeks of treatment and changed as needed. After that, the hormone levels usually only have to be checked once a year.

Doctors disagree about whether subclinical hypothyroidism should be treated.

Further information

When people are ill or need medical advice, they usually go to see their family doctor first. Information about health care in Germany can help you to navigate the German health care system and find a suitable doctor. You can use this list of questions to prepare for your appointment.

Bekkering GE, Agoritsas T, Lytvyn L et al. Thyroid hormones treatment for subclinical hypothyroidism: a clinical practice guideline. BMJ 2019; 365: l2006.

Bundesinstitut für Risikobewertung (BfR). Jodversorgung in Deutschland wieder rückläufig – Tipps für eine gute Jodversorgung. 2021.

Bundesinstitut für Risikobewertung (BfR). Verwendung von Mineralstoffen in Lebensmitteln. Toxikologische und ernährungsphysiologische Aspekte. Teil II. Berlin: BfR Wissenschaft; 2004.

Chaker L, Bianco AC, Jonklaas J, Peeters RP. Hypothyroidism. Lancet 2017; 390(10101): 1550-1562.

Deutsche Gesellschaft für Allgemeinmedizin und Familienmedizin (DEGAM). Erhöhter TSH-Wert in der Hausarztpraxis (S2k-Leitlinie). AWMF-Registernr.: 053-046. 2023.

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Jameson JL, Mandel SJ, Weetman AP. Disorders of the Thyreoid Gland. In: D. L. Kaspers, S. L. Hauser, J. L. Jameson et al. (Ed). Harrison's Principles of Internal Medicine. McGraw-Hill Education; 2015.

National Institute for Health and Care Excellence (NICE). Thyroid disease: assessment and management. 2019.

Pearce SH, Brabant G, Duntas LH et al. ETA Guideline: Management of Subclinical Hypothyroidism. Eur Thyroid J 2013; 2(4): 215-228.

Persani L, Brabant G, Dattani M et al. 2018 European Thyroid Association (ETA) Guidelines on the Diagnosis and Management of Central Hypothyroidism. Eur Thyroid J 2018; 7(5): 225-237.

Reyes Domingo F, Avey MT, Doull M. Screening for thyroid dysfunction and treatment of screen-detected thyroid dysfunction in asymptomatic, community-dwelling adults: a systematic review. Systematic Reviews 2019; 8(1): 260.

Schübel J, Feldkamp J, Bergmann A et al. Latente Hypothyreose des Erwachsenen. Dtsch Arztebl Int 2017; 114(25): 430-438.

UK National Screening Committee (UK NSC). Screening for thyroid dysfunction in adults. External review against programme appraisal criteria for the UK National Screening Committee (UK NSC). 2018.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Updated on May 28, 2024

Next planned update: 2027


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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