Overactive Thyroid
Hyperthyroidism: the thyroid producing too much hormone, speeding up many body processes.
Last revised
Key takeaways
- Main test: low TSH, with high T4 or T3
- Most common cause: Graves' disease
- Most useful single change: See your doctor about unexplained weight loss with palpitations or tremor.
- Commonest mistake: Putting palpitations and anxiety down to stress without a thyroid test.
- See a doctor if any of the signs under "When to get help" below apply to you.
Why it matters
It causes weight loss, palpitations and anxiety that are often put down to stress, and it carries real heart and bone risks if untreated.
The numbers, in one place
| Measure | Figure |
|---|---|
| Main test | low TSH, with high T4 or T3 |
| Most common cause | Graves' disease |
| Treatments | antithyroid medicines, radioactive iodine, or surgery |
| Methimazole warning | sore throat or fever needs an urgent blood count |
| Associated risks | atrial fibrillation and osteoporosis |
What helps
- See your doctor about unexplained weight loss with palpitations or tremor
- Report eye symptoms, which need assessment by an eye doctor in Graves' disease
- Take antithyroid medicine exactly as prescribed
- Quit smoking, which considerably worsens thyroid eye disease
What to avoid
- Putting palpitations and anxiety down to stress without a thyroid test
- Ignoring a sore throat or fever while taking methimazole
- Stopping treatment when symptoms improve
In depth
In hyperthyroidism the thyroid makes more hormone than your body needs, and processes that thyroid hormone controls speed up. Your heart beats faster and sometimes irregularly, you burn energy more quickly, you feel hot and restless, and your gut moves faster. Over time, excess hormone also speeds up the turnover of bone, so calcium is lost faster than it is replaced. These effects explain why an overactive thyroid matters even when you feel you are coping with the symptoms.
Graves' disease, the most common cause, is an autoimmune condition. The immune system makes antibodies that mimic TSH and switch the thyroid on continuously, regardless of how much hormone is already circulating. Other causes include one or more nodules that produce hormone independently, more common in older adults, and thyroiditis, in which an inflamed gland leaks stored hormone for a few weeks or months. Taking too much thyroid medicine produces the same picture.
The cause matters because it changes the treatment. Thyroiditis usually settles on its own and does not respond to antithyroid medicines, while Graves' disease may go into remission after a course of medicine, and overactive nodules usually do not. Graves' disease can also affect the eyes and the skin over the shins, which needs its own attention. Your doctor will usually want to identify the cause before deciding on long-term treatment.
Signs and symptoms
- Unexplained weight loss despite a normal or increased appetite
- Fast, pounding or irregular heartbeat
- Shaky hands, nervousness, irritability or trouble sleeping
- Feeling hot and sweating more than those around you
- More frequent bowel movements
- Weakness in the thigh and upper arm muscles, such as difficulty climbing stairs
- Gritty, red or bulging eyes, or double vision, in Graves' disease
Causes and risk factors
- Graves' disease, an autoimmune condition
- One or more thyroid nodules that make hormone on their own
- Thyroiditis, including thyroid inflammation after pregnancy
- Taking more thyroid hormone medicine than you need
- Large amounts of iodine from some medicines, contrast dyes or supplements in susceptible people
- A personal or family history of autoimmune disease
How it is checked
A blood test showing low TSH with raised free T4, T3 or both confirms that the thyroid is overactive. Your doctor will then look for the cause. Antibody tests for TSH receptor antibodies can confirm Graves' disease, and a physical exam may find an enlarged gland, a nodule or tenderness that suggests thyroiditis.
A radioactive iodine uptake scan shows how actively the gland takes up iodine: high, even uptake points to Graves' disease, bright spots point to overactive nodules, and low uptake suggests thyroiditis or excess medicine. This scan is not done during pregnancy or breastfeeding. Ultrasound can show blood flow and nodules, and an ECG may be done if your heart rate is fast or irregular.
Related topics
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- Vitamin D: What the Evidence Actually Says (Nutrition)
- Rate of Weight Loss: Sorting the Evidence From the Noise (Weight Management)
Where to go next
- Overactive Thyroid: A Beginner-Friendly Start
- Answers to the Common Questions on Overactive Thyroid
- Thyroid and Hormones: The Complete Guide
- What the Guidance Really Says About Thyroid Function Tests
- Thyroid Lumps: What Published Guidance Supports
When to get help
Contact your doctor the same day for a sore throat, mouth sores, fever or bruising while taking methimazole or propylthiouracil — these can indicate a dangerous drop in white blood cells and need an immediate blood count. Call 911 for fever with agitation, a very rapid heart rate, vomiting and confusion, which can indicate thyroid storm. Report double vision or eye pain to your doctor urgently.
Where this comes from
- American Thyroid Association — Hyperthyroidism (Overactive)
- National Institute of Diabetes and Digestive and Kidney Diseases — Hyperthyroidism (Overactive Thyroid)
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.