Symptoms of overactive thyroid can include:
- feeling nervous, irritable or hyperactive
- having tremors (shaking)
- being unable to cope with heat
- sweating more than usual
- losing weight, with or without an increased appetite
- feeling tired
- muscle weakness
- having an increased heart rate (palpitations)
- irregular menstrual periods if you’re a woman
- having more frequent bowel movements or diarrhoea
- thinning or loss of hair
- an enlarged thyroid gland (goitre), which causes a lump to develop in your throat
- abnormal breast growth in men (gynaecomastia)
These symptoms aren’t always caused by overactive thyroid but if you have them it’s best to see your GP.
Your GP will ask about your symptoms and examine you, and may ask you about your medical history. They may also ask if you have a family history of autoimmune disease or thyroid disease.
Your GP may take a blood sample. Often, the blood test begins by measuring your levels of thyroid stimulating hormone (TSH). TSH is made in the pituitary gland in your brain and controls the production of thyroxine and triiodothyronine.
If your thyroid gland is overactive, your level of TSH will be low. If this is shown in your blood test, your thyroid hormone levels will also be measured.
If blood tests show high levels of either T4 or T3 (or both) and a low level of TSH , this confirms an overactive thyroid. Your GP will either advise you about your treatment options or refer you to an endocrinologist (a specialist in identifying and treating thyroid conditions).
You may need to have a radioisotope scan. This involves having a small amount of a radioactive substance injected into your blood, which is taken up by your thyroid gland. Scans of your thyroid gland will show up any overactive areas.
Treatment aims to return your levels of thyroid hormones to normal.
Your doctor may prescribe you antithyroid medicines (either carbimazole or propylthiouracil) to reduce the production of thyroid hormone in your thyroid gland. You will need to take these medicines for 12 to 18 months. These medicines can sometimes lead to an underactive thyroid (hypothyroidism), so you will need regular blood tests to check your levels of thyroid hormones.
Your doctor may also prescribe you beta-blockers, such as propranolol, to help manage the symptoms of overactive thyroid until your hormone levels return to normal. If you have asthma, you should never take a beta-blocker as this can make your asthma worse. Your doctor may instead offer you calcium-channel blockers, such as verapamil or diltiazem, to slow down a fast heart rate caused by an overactive thyroid. These medicines are usually only prescribed if you’re having symptoms or during a thyroid storm.
Beta blockers (or calcium channel blockers) don’t treat the underlying problem. But they should protect your heart from high levels of thyroid hormone while other treatments lower your thyroid hormone levels back to normal.
When you’re diagnosed with hyperthyroidism and receiving treatment, you’ll need regular blood tests. This helps manage your condition and ensures you’re receiving the right dosage of antithyroid medicines. Thyroid function tests measure levels of thyroid-stimulating hormones (TSH) in your blood and may include tests of T4 and T3 levels. Your blood tests will usually be:
- every one to two months at the beginning of starting antithyroid medicines or in the first year after radioactive iodine treatment
- every six to 12 months when you’re on long-term medication
- once a year after you’ve had thyroid surgery
Be aware that results from different labs can vary so aren’t always comparable. Plus, there are different ranges used if you’re pregnant. If you have a specific query about your blood test results and what they mean, speak to your doctor.
If antithyroid medicines aren’t effective for you, then your doctor might suggest radioiodine treatment. This involves taking iodine as a tablet or drink, which is taken up by your thyroid gland. As the radioactivity builds up, it destroys some of your thyroid tissue, so the gland produces less thyroid hormones. Usually, you will be given a single dose of radioiodine sufficient to stop all your thyroid activity. If radioiodine treatment successfully reduces the activity of your thyroid gland, you will need to take levothyroxine every day for the rest of your life. Levothyroxine is a thyroid hormone replacement medicine.
Radioiodine treatment is usually offered as an alternative to surgery when antithyroid medicines aren’t suitable or are ineffective. However, radioactive iodine isn’t suitable if you’re pregnant or breastfeeding. It also isn’t practical if you have young children to care for because your contact with them will be restricted for four weeks after receiving radioactive iodine.
Your doctor may suggest having an operation to remove all or part of your thyroid gland (called a thyroidectomy). Before surgery, your thyroid hormone levels will need to be controlled. This is because an overactive thyroid can increase your risk of complications when you have a general anaesthetic.
After surgery, you may need to take levothyroxine every day for the rest of your life. Surgery is offered as an alternative to medicines and radioactive iodine when they are either ineffective or not practical. Surgery may also be a good option if you need a more immediate response to treatment. This is because surgery is immediately effective. Radioactive iodine can take up to 12 months to take effect and doesn’t work every time. If you need more information, speak to your doctor.
The most common causes of overactive thyroid are described below.
- Graves’ disease. This is an autoimmune disease. Your immune system produces antibodies that trigger your thyroid gland to produce more thyroid hormone than your body needs. Antibodies are proteins produced by your immune system that usually fight against bacteria and viruses.
- Nodular thyroid disease. Lumps or nodules develop in your thyroid gland and produce thyroid hormones.
- Certain medicines (eg amiodarone). Iodine in medicines can trigger your thyroid gland to produce thyroid hormones.
If left untreated, overactive thyroid can increase your risk of heart failure. You may also develop problems with your vision. Rarely, you may develop a life-threatening reaction called a thyroid storm (thyrotoxic crisis). The symptoms of a thyroid storm include having a very fast heart beat, fever and jaundice. This is where your skin and the whites of your eyes appear yellow in colour.
If you’re a woman, having an overactive thyroid can increase your risk of:
- oligomenorrhoea (infrequent or very light menstrual periods)
- amenorrhoea (the absence of menstrual periods)
If you become pregnant, having overactive thyroid may increase your risk of having a miscarriage, premature birth or a baby with low birth weight.
I am due to start radioiodine treatment for overactive thyroid. Do I need to take any precautions?
Yes, you will need to take some precautions before and after radioiodine treatment.
Radioiodine treatment involves using radioactive iodine to destroy some or all of your thyroid gland to slow down production of thyroid hormones.
If you’ve been taking antithyroid medicines, you will need to stop taking them before your radioiodine treatment starts.
There is some evidence that having too much iodine in your diet can reduce the effectiveness of radioiodine treatment. If you're taking any medicines or food supplements containing iodine, kelp (a seaweed that contains iodine) or cod liver oil, you will need to stop taking them.
After having radioiodine treatment, your body will contain some radioactivity. After having radioiodine treatment, the Royal College of Physicians suggests you:
- limit contact with children and pregnant women
- stay more than an arm’s length away from other people
- sleep alone
- don’t go to busy places such as cinemas, pubs and restaurants
- don’t share your towels and face cloths
- wash your crockery and cutlery thoroughly
- flush the toilet twice after urinating
How long you need to follow the precautions for will depend on how much radioiodine you were given. Your doctor will be able to give you more advice.
Radioiodine may trigger airport security alarms up to eight weeks after treatment. You should therefore carry a letter about the treatment if you travel in this period. If you have thyroid eye disease, radioiodine can worsen your symptoms, so you may need to take steroid tablets.
If you’re a woman, you shouldn’t get pregnant for six months after having your treatment. And men should wait at least four months before trying for a baby.
If you have any concerns or questions about radioiodine treatment, talk to your doctor.
What are the dangers of untreated overactive thyroid?
If left untreated, overactive thyroid can become life-threatening. It’s important to seek medical help and take any treatment that your doctor advises you to.
If overactive thyroid isn't treated properly, your symptoms will get worse over time. You will continue to lose weight, become very tired, develop problems with your vision and have a fast or irregular heartbeat (atrial fibrillation).
Atrial fibrillation can increase your risk of having a heart attack and/or stroke. This is because your blood doesn't flow properly through your heart, so a blood clot can form. If a clot forms, it can block blood supply in your heart and cause a heart attack, or travel to your brain and cause a stroke.
Rarely, you may develop a life-threatening reaction called a thyroid storm (thyrotoxic crisis). This may be triggered by an infection, surgery or a trauma (including childbirth). A thyroid storm is extremely rare and you’re unlikely to experience it. However, symptoms include:
- fast or irregular heartbeat
Thyrotoxic crisis is a medical emergency and requires urgent hospital treatment. If you need more information about the dangers of untreated overactive thyroid, speak to you doctor.
What is thyroid eye disease and will I get it if I have overactive thyroid?
Thyroid eye disease is swelling of the soft tissues surrounding your eyes, which gives them a bulging appearance. Your eyes may become dry, red and puffy. Occasionally it can lead to double vision. You’re more likely to develop thyroid eye disease if you have an overactive thyroid gland caused by Graves’ disease.
Graves' disease is the most common cause of overactive thyroid. It’s an autoimmune condition that develops when your immune system produces antibodies that trigger your thyroid gland to release thyroid hormones. Antibodies are proteins produced by your immune system that usually fight against bacteria and viruses.
About one in three people with Graves’ disease develop thyroid eye disease. If you smoke, you’re eight times more likely to develop thyroid eye disease than non-smokers.
Thyroid eye disease occurs when the soft tissues surrounding your eyes swell up, giving your eyes a bulging appearance. Your eyes may become dry, red and puffy. You may have a gritty feeling in your eyes and a feeling of pressure behind them. Although dryness is a common feature, you may also find that your eyes frequently water and produce more tears than usual. Occasionally, thyroid eye disease can lead to double vision or limited movement of your eyeball.
If you get double vision or limited movement of your eyeball, it can affect your ability to read and make driving dangerous. If you develop double vision then you must stop driving and let the Driving and Licensing Authority (DVLA) know. It’s illegal to drive with double vision that isn’t controlled with glasses. If your double vision is treated and becomes controlled by glasses, then you will be able to drive again.
If you have any problems with your vision, it's important to talk to your GP who will refer you to an ophthalmologist (a doctor who specialises in eye health, including eye surgery).
The type of treatment you have for thyroid eye disease depends on your symptoms and how severe they are. For example, you may be prescribed:
- eye drops to treat dryness
- steroids to reduce swelling
If steroids and other treatments don’t work, your doctor may suggest radiotherapy or thyroidectomy surgery.
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Will having an overactive thyroid affect my ability to become pregnant or lead to complications during my pregnancy?
If you’re a woman, having overactive thyroid can reduce your fertility, making it more difficult for you to get pregnant. It may also lead to complications during pregnancy and birth. It's important to tell your doctor if you plan to become pregnant, so your thyroid hormone levels can be kept under control
Overactive thyroid can interfere with your menstrual cycle, leading to irregular or infrequent periods. This may affect your ability to ovulate, making it more difficult for you to get pregnant. You're more likely to become pregnant if your thyroid hormones are at a healthy level. This is why it's important that your overactive thyroid is treated and kept under control.
If you have overactive thyroid that isn't treated and you become pregnant, you're more at risk of complications. These include miscarriage, premature birth and your baby having a low birth weight. Even if your overactive thyroid is being treated, or has been treated successfully, there are still precautions you need to take if you plan to have a baby.
Before you become pregnant, your antithyroid medicine should be switched from carbimazole to propylthiouracil. If you have been treated with radioiodine, you shouldn't get pregnant for six months afterwards as the radioiodine could damage your baby’s thyroid gland. And men who have had radioiodine treatment should wait four months before fathering a child.
If you have been successfully treated, there is still a chance that you could develop thyroid-related problems during or after the pregnancy. Therefore, your thyroid hormone levels will be closely monitored.
If you have overactive thyroid and are pregnant, you will be referred to an obstetrician (a doctor who specialises in pregnancy and childbirth). They will help make sure that any medicines used to treat your condition won't affect your pregnancy or developing baby.
You will need to be monitored regularly. Once you’re past your first trimester (13 weeks) of pregnancy, the dose of propylthiouracil can usually be reduced or stopped. If you're planning to breastfeed, you can still take antithyroid medicines but will need to take the lowest dose possible. Your baby's development will also need to be closely monitored.
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