In an overactive thyroid (hyperthyroidism), the thyroid produces too many hormones (fT3 and fT4). These hormones control the entire metabolism: heartbeat, body temperature, energy expenditure, nervous system and digestion. An excess can cause the body to run at full speed permanently.⁵
Overt vs. subclinical
In overt hyperthyroidism, TSH is reduced and fT3/fT4 are elevated — symptoms are usually present. In subclinical hyperthyroidism, only the TSH is reduced, while fT3/fT4 are still within the normal range — often with few symptoms. Even subclinical hyperthyroidism can, in the long term, increase the risk of atrial fibrillation and osteoporosis and should be monitored by a doctor.⁵
2. Causes: Graves' disease and autonomous nodules
Cause 1Graves' disease — most common cause in younger people
An autoimmune disease in which TSH receptor antibodies (TRAb) stimulate the thyroid to produce hormones uncontrollably. Women are affected considerably more often.
The classic feature is the so-called Merseburg triad: enlarged thyroid (goiter), rapid pulse (tachycardia) and protruding eyes (exophthalmos).
Smoking considerably worsens Graves' disease
The eye involvement in particular (thyroid eye disease) usually increases considerably with smoking. Stopping smoking is one of the most important measures.⁶
Cause 2Autonomous thyroid nodules — more common in older people
Nodules that produce hormones independently — regardless of TSH control. Either a single nodule (toxic adenoma) or several (multifocal autonomy). More common in older patients, often as a consequence of longer-term iodine deficiency. The onset is usually insidious.
Other causes
Thyroiditis (thyroid inflammation) — usually temporary and self-limiting
Too high a levothyroxine dose during existing treatment of an underactive thyroid
Iodine excess from iodine-containing contrast media (e.g. before a CT scan) or medications
Amiodarone (a heart rhythm drug) — amiodarone-induced overactivity is complex and is usually treated jointly by cardiology and endocrinology
3. Symptoms
The symptoms can vary greatly from person to person. Typical ones are:⁵
Inner restlessness, nervousness, irritability
Sleep disturbances
Unintentional weight loss despite a normal or increased appetite
Fatigue and exhaustion — paradoxically despite an increased metabolism
Menstrual disturbances in women
In Graves' disease additionally: protruding eyes (exophthalmos), a feeling of pressure behind the eyes, double vision
Atypical symptoms in older patients
Instead of restlessness and weight loss, atrial fibrillation, heart failure or depressive mood are sometimes in the foreground. An overactive thyroid is then easily overlooked — with every newly occurring episode of atrial fibrillation, thyroid function should be checked.
4. Complications
Atrial fibrillation: The most common cardiovascular complication. Can be associated with an increased risk of stroke. With every newly occurring episode, thyroid function should be checked.
Osteoporosis: Thyroid hormones can accelerate bone breakdown. Long-term untreated hyperthyroidism increases the fracture risk — especially in postmenopausal women.
Thyroid eye disease (in Graves' disease): Autoimmune inflammation of the tissue behind the eyes. Possible symptoms: protruding eyes, a feeling of pressure, double vision, sensitivity to light. Occurs in some Graves' patients. Stopping smoking is usually one of the most important steps; in severe cases, cortisone or surgical measures, among others, may be considered.⁶
Heart failure: Long-term tachycardia can strain the heart and, over time, lead to a weakening of heart function.
5. Diagnosis
TSH (screening value): Reduced in hyperthyroidism — the most important first indication.⁵
fT3 and fT4: Elevated in overt overactivity.
TRAb antibodies: Usually positive in Graves' disease and considered diagnostically conclusive. Can be detectable even before the first symptoms.
TPO antibodies: Can also be positive, but are less specific.
Thyroid ultrasound: Assesses size, nodules and blood flow. In Graves' disease, strongly increased blood flow is often visible. Fast, painless, radiation-free.
Scintigraphy: Shows whether nodules produce hormones independently (hot nodules = autonomous) or not (cold nodules = possibly further evaluation). Usually indispensable when autonomy is suspected.
6. Treatment: antithyroid drugs, radioiodine, surgery
Which therapy is sensible in an individual case depends on the cause, the severity and individual factors. The decision is usually made by the treating endocrinologist.
Antithyroid drugs — first-line medication
Thiamazole / carbimazole — first-line therapy in Graves' disease
Inhibit hormone production in the thyroid. In Graves' disease, a therapeutic trial over several months up to about a year is often sensible. In a relevant share of Graves' patients, remission occurs during therapy.⁵ In case of relapse or autonomy: Consider radioiodine therapy or surgery.
Agranulocytosis warning — act immediately with fever or a sore throat!
Antithyroid drugs can, in rare cases, lead to a life-threatening drop in white blood cells. With fever, a sore throat or mouth ulcers while on thiamazole or carbimazole:
→ Have a blood count checked immediately
→ Stop the medication immediately
→ Seek medical advice — do not wait for the next appointment⁵
Beta blockers (e.g. propranolol) — symptomatic at the start
Can be used in addition to quickly relieve symptoms such as a racing heart, tremor and restlessness. They usually do not affect hormone production itself.
Radioiodine therapy
Radioiodine therapy — often a permanent solution
Radioactive iodine accumulates specifically in the thyroid and destroys the overactive tissue. Often used when antithyroid drugs do not work sufficiently or a relapse occurs. Inpatient stay: In Germany, usually a few days are required by law. Afterwards: Lifelong levothyroxine replacement is usually necessary.¹
Surgery (thyroidectomy)
Thyroidectomy — for mechanical symptoms or suspected nodules
Partial or complete removal of the thyroid. Considered with a large goiter causing swallowing or breathing difficulties, when nodules are suspected of being malignant, or when other therapies are not an option. Afterwards: Usually lifelong levothyroxine intake. Possible risks: Injury to the vocal cord nerve or damage to the parathyroid glands — usually rare in experienced centers.
A thyroid storm is the most severe and life-threatening complication of an overactive thyroid.⁵
With these signs, call 112 immediately — intensive care unit!
High fever · Heavy sweating · Extreme tachycardia, atrial fibrillation, heart failure · Disturbance of consciousness up to coma · Vomiting, diarrhea, dehydration · Severe restlessness, confusion
Possible triggers
Iodine-containing contrast media in unrecognized or inadequately treated hyperthyroidism
Severe infections
Surgery
Stopping antithyroid drugs
Trauma
Prevention: always disclose the overactive thyroid
Before CT scans with contrast media, before surgery and when amiodarone is being prescribed, be sure to inform the treating doctor.
8. Living with an overactive thyroid
Contrast media: Before every CT or angiography with iodine-containing contrast media, be sure to inform the radiology department. In certain situations, prior protection with antithyroid drugs can be sensible.
Lab checks: During ongoing therapy, TSH, fT3 and fT4 are checked at regular intervals — more often at first, less often once stably adjusted. While on antithyroid drugs, a blood count can additionally be recommended (agranulocytosis monitoring).
Diet: With active overactivity, usually avoid iodine-containing supplements and seaweed/kelp. Iodized table salt in normal amounts is usually not a problem in mild overactivity. After radioiodine or surgical treatment, dietary iodine is usually no longer an issue.
Smoking: Considerably worsens the course of Graves' disease and, in particular, thyroid eye disease. Stopping smoking is one of the most important measures.⁶
Stress: Can possibly trigger Graves' disease and worsen its course. Stress management is often recommended as part of the therapy.
Medications: Amiodarone, lithium and certain immunotherapies can affect thyroid function. Have thyroid levels checked regularly with these medications. More: Supplements and medications.
How brite helps you with an overactive thyroid
Antithyroid drugs, beta blockers, lab appointments, levothyroxine after treatment — brite keeps track and reminds you on time.
Intake reminder — antithyroid drugs, beta blockers, levothyroxine after radioiodine/surgery: brite reminds you on time. Set up a reminder
Interaction check — check antithyroid drugs in combination with other medications for free. Check now
Health history — document TSH, fT3, fT4, weight, pulse and symptoms. Track your history
Digital medication plan — all medications clearly organized for endocrinology, your GP and radiology. Go to medication plan
In Graves' disease, remission occurs in a relevant share of those affected during antithyroid drug therapy. In case of relapse or autonomous nodules, radioiodine therapy or surgery are usually permanent solutions — afterwards, levothyroxine is usually taken as hormone replacement, but the overactivity is then resolved.⁵
Antithyroid drugs can, in rare cases, cause a life-threatening drop in white blood cells. With fever, a sore throat or mouth ulcers while on thiamazole or carbimazole, have a blood count checked immediately, stop the medication and seek medical advice — do not wait for the next appointment.⁵
The most severe complication of an overactive thyroid. Signs are high fever, extreme racing of the heart, disturbance of consciousness up to coma. Possible triggers include iodine-containing contrast media in unrecognized hyperthyroidism or stopping antithyroid drugs. Call 112 immediately — treatment in the intensive care unit!⁵
Iodine-containing supplements and seaweed/kelp should usually be avoided. Iodized table salt in normal amounts is usually not a problem with a mild overactivity. After radioiodine or surgical treatment, dietary iodine is usually no longer an issue.
Iodine-containing contrast media (e.g. for a CT or angiography) can trigger a thyroid storm in unknown or inadequately treated hyperthyroidism. Always inform the radiology department about the overactive thyroid — in certain situations, prior protection with antithyroid drugs can be sensible.
Usually yes — levothyroxine as hormone replacement. Intake is usually well tolerated and is dosed individually and checked regularly by blood test. More: Taking levothyroxine correctly.⁵
Smoking intensifies the autoimmune reaction and is considered one of the most important risk factors for the development and worsening of thyroid eye disease (eye involvement). Stopping smoking can usually considerably improve the course.⁶
An autoimmune inflammation of the tissue behind the eyes in Graves' disease. Possible symptoms: protruding eyes, a feeling of pressure, double vision, sensitivity to light. Occurs in some Graves' patients. Stopping smoking is one of the most important steps; in severe cases, cortisone or surgical measures, among others, may be considered.⁶
Yes — atrial fibrillation is the most common cardiovascular complication of hyperthyroidism and can be the first and only symptom in older patients. With every newly occurring episode of atrial fibrillation, thyroid function should usually be checked.
Deutsche Gesellschaft für Nuklearmedizin (DGN): Leitlinien. nuklearmedizin.de
Medical disclaimer: This article is for general information and does not replace medical advice, diagnosis or treatment. The choice of medication and dosages are always determined individually by the treating doctor. With fever, extreme racing of the heart and disturbance of consciousness in a known overactivity, call the emergency number 112 immediately (suspected thyroid storm). With fever or a sore throat while on antithyroid drugs, have a blood count checked immediately (agranulocytosis). Always coordinate contrast media examinations in advance with the treating practice. Last updated: April 2026.
