With an overactive thyroid (hyperthyroidism), the thyroid gland 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 make the body run at full speed all the time.⁵
Overt vs. subclinical (latent)
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, over 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 — the 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 much more often.
Classic is the so-called Merseburg triad: an enlarged thyroid (goiter), a fast pulse (tachycardia) and protruding eyes (exophthalmos).
Smoking makes Graves' disease considerably worse
The eye involvement in particular (thyroid eye disease) usually increases significantly with smoking. Quitting smoking is one of the most important measures.⁶
Cause 2Autonomous thyroid nodules — more common in older people
Nodules that produce hormones on their own — independently of TSH control. Either a single nodule (toxic adenoma) or several (multifocal autonomy). More common in older patients, often as a result of long-term iodine deficiency. The onset is usually gradual.
Other causes
Thyroiditis (inflammation of the thyroid) — usually temporary and self-limiting
Too high a levothyroxine dose during existing treatment for an underactive thyroid
Iodine excess from iodine-containing contrast agents (e.g. before a CT scan) or medications
Amiodarone (a heart rhythm medication) — amiodarone-induced overactivity is complex and is usually managed jointly by cardiology and endocrinology
3. Symptoms
Symptoms can vary greatly from person to person. Typical ones are:⁵
Inner restlessness, nervousness, irritability
Sleep problems
Unintentional weight loss despite a normal or increased appetite
Heart racing, palpitations — in some cases progressing to atrial fibrillation
A fine trembling of the hands (tremor)
Excessive sweating, intolerance to heat
Diarrhea or more frequent bowel movements
Muscle weakness (especially in the thighs)
Hair loss, brittle nails
Fatigue and exhaustion — paradoxically, despite an increased metabolism
Menstrual cycle problems in women
With 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, sometimes atrial fibrillation, heart failure or low mood are the dominant features. An overactive thyroid is then easily missed — whenever a new episode of atrial fibrillation occurs, thyroid function should be checked.
4. Complications
Atrial fibrillation: The most common cardiovascular complication. It can be associated with an increased risk of stroke. Whenever a new episode occurs, thyroid function should be checked.
Osteoporosis: Thyroid hormones can speed up bone loss. Long-term untreated hyperthyroidism increases the risk of fractures — especially in women after menopause.
Thyroid eye disease (in Graves' disease): An autoimmune inflammation of the tissue behind the eyes. Possible symptoms: protruding eyes, a feeling of pressure, double vision, sensitivity to light. It occurs in a portion of Graves' patients. Quitting smoking is usually one of the most important steps; in severe cases, options include corticosteroids or surgical measures.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 clue.⁵
fT3 and fT4: Elevated in overt overactivity.
TRAb antibodies: Usually positive in Graves' disease and considered diagnostically conclusive. They 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, a strongly increased blood flow is often visible. Quick, painless, radiation-free.
Scintigraphy (thyroid scan): Shows whether nodules produce hormones on their own (hot nodules = autonomous) or not (cold nodules = possibly further investigation). Usually indispensable when autonomy is suspected.
6. Treatment: antithyroid drugs, radioiodine, surgery
Which treatment makes sense in an individual case depends on the cause, the severity and individual factors. The decision is usually made by your treating endocrinologist.
Antithyroid drugs — first-line drug treatment
Thiamazole (methimazole) / carbimazole — first-line treatment for Graves' disease
They inhibit hormone production in the thyroid. In Graves' disease, a treatment trial over several months to about a year is often sensible. A relevant proportion of Graves' patients go into remission on this therapy.⁵ In case of relapse or autonomy: consider radioiodine therapy or surgery.
Agranulocytosis warning — act immediately if you get a fever or sore throat!
Antithyroid drugs can in rare cases cause a life-threatening drop in white blood cells. If you develop a fever, sore throat or mouth ulcers while taking thiamazole or carbimazole:
→ Have a blood count done immediately
→ Stop the medication immediately
→ Seek medical advice — don't wait for your next appointment⁵
Beta blockers (e.g. propranolol) — for symptoms at the start
Can be used as an add-on to quickly relieve symptoms such as heart racing, tremor and restlessness. They generally 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 don't work well enough or a relapse occurs. Inpatient stay: In Germany this usually requires a hospital stay of a few days (for radiation protection); the rules vary by country. Afterwards: Lifelong levothyroxine replacement is usually necessary.¹
Surgery (thyroidectomy)
Thyroidectomy — for mechanical symptoms or suspicious nodules
Partial or complete removal of the thyroid. Considered for a large goiter with swallowing or breathing difficulties, for nodules suspected of being malignant, or when other treatments are not an option. Afterwards: Lifelong levothyroxine, as a rule. Possible risks: injury to the vocal cord nerve (recurrent laryngeal 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
Call 112 immediately if you notice these signs — intensive care!
High fever · Heavy sweating · Extreme tachycardia, atrial fibrillation, heart failure · Impaired consciousness up to coma · Vomiting, diarrhea, dehydration · Severe restlessness, confusion
Possible triggers
Iodine-containing contrast agents in unrecognized or inadequately treated hyperthyroidism
Severe infections
Surgery
Stopping antithyroid drugs
Trauma
Prevention: always tell people about your overactive thyroid
Before CT scans with contrast agents, before surgery, and when amiodarone is prescribed, be sure to inform your treating doctor.
8. Living with an overactive thyroid
Contrast agents: Before any CT scan or angiography with iodine-containing contrast, be sure to inform the radiology team. In certain situations, protective pre-treatment with antithyroid drugs can be sensible.
Lab checks: During ongoing treatment, TSH, fT3 and fT4 are checked at regular intervals — more often at first, less often once stable. While on antithyroid drugs, a blood count may also be recommended (to monitor for agranulocytosis).
Diet: With an active overactive thyroid, generally avoid iodine-containing supplements and seaweed/kelp. 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.
Smoking: Significantly worsens the course of Graves' disease and especially thyroid eye disease. Quitting smoking is one of the most important measures.⁶
Stress: May possibly trigger Graves' disease and worsen its course. Stress management is often recommended as part of treatment.
Medications: Amiodarone, lithium and certain immunotherapies can affect thyroid function. Have your thyroid levels checked regularly while on these medications. Learn more: Supplements and medication.
How brite helps you with an overactive thyroid
Antithyroid drugs, beta blockers, lab appointments, levothyroxine after treatment — brite keeps track and reminds you right on schedule.
Medication reminders — Antithyroid drugs, beta blockers, levothyroxine after radioiodine/surgery: brite reminds you right on schedule. Set up a reminder
Interaction check — Check antithyroid drugs in combination with other medications for free. Check now
Health tracking — Record your TSH, fT3, fT4, weight, pulse and symptoms. Track your history
Digital medication plan — all your medications clearly laid out for your endocrinologist, GP and radiology team. Go to medication plan
In Graves' disease, a relevant proportion of those affected go into remission on antithyroid drug therapy. For relapses 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. If you develop a fever, sore throat or mouth ulcers while taking thiamazole or carbimazole, immediately have a blood count done, stop the medication and seek medical advice — don't wait for your next appointment.⁵
The most severe complication of an overactive thyroid. Signs are a high fever, extreme heart racing, and impaired consciousness up to coma. Possible triggers include iodine-containing contrast agents in unrecognized hyperthyroidism or stopping antithyroid drugs. Call 112 immediately — treatment in intensive care!⁵
Iodine-containing supplements and seaweed/kelp should generally 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 agents (e.g. for a CT scan or angiography) can trigger a thyroid storm in an unrecognized or inadequately treated overactive thyroid. Always inform the radiology team about your overactive thyroid — in certain situations, protective pre-treatment with antithyroid drugs can be sensible.
Usually yes — levothyroxine as hormone replacement. It is usually well tolerated, dosed individually and checked regularly with a blood test. Learn more: How to take 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). Quitting smoking can usually significantly 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. It occurs in a portion of Graves' patients. Quitting smoking is one of the most important steps; in severe cases, options include corticosteroids or surgical measures.⁶
Yes — atrial fibrillation is the most common cardiovascular complication of an overactive thyroid and can be the first and only symptom in older patients. Whenever a new episode of atrial fibrillation occurs, thyroid function should generally be checked.
German Society of Nuclear Medicine (DGN): Guidelines. nuklearmedizin.de
Medical disclaimer: This article is for general information only and is not a substitute for medical advice, diagnosis or treatment. The choice of medication and dosages are always determined individually by your treating doctor. If you develop a fever, extreme heart racing and impaired consciousness with a known overactive thyroid, call the emergency number 112 immediately (suspected thyroid storm). If you get a fever or sore throat while on antithyroid drugs, have a blood count done immediately (agranulocytosis). Always discuss contrast-agent examinations with your treating practice in advance. Last updated: April 2026.
