Overactive thyroid

Your thyroid is a small, butterfly-shaped gland in your neck. It produces 2 thyroid hormones: tri-iodothyronine (T3) and thyroxine (T4). Thyroid hormones help your body use energy, stay warm and keep your brain, heart, muscles and other organs working as they should.

 Image credit: Canva

Thyroid problems can affect anyone, but are more common in women than men.

An overactive thyroid can be caused by a number of conditions:

• Graves’ disease. This is the most common cause. It is an autoimmune disease in which your body’s immune system mistakenly attacks your thyroid gland. Sometimes this condition runs in families.
• Thyroid nodules. These are benign (non-cancerous) lumps that grow on your thyroid. They can produce extra thyroid hormones. Read more about thyroid nodules.
• Too much iodine in your body. This can be caused by taking iodine supplements such as kelp or seaweed
• Thyroiditis (inflammation of your thyroid gland). This can be caused by a virus or can happen soon after having a baby. 
• Some medicines such as lithium or amiodarone can cause an overactive thyroid.
• Thyroid cancer. This is rare, but a thyroid cancer can affect the production of thyroid hormones.

People with an overactive thyroid may have no symptoms at all, or symptoms may start off mild and then gradually get worse.

Symptoms may include:

• losing weight, even though you are eating the same amount or more than usual
• feeling nervous, anxious, moody, weak or tired
• tremor (shaky hands)
• palpitations (fast or ‘thumping’ heartbeat)
• problems breathing
• feeling hot and sweaty
• having looser, more frequent, bowel movements (poo) than usual
• skin problems such as a rash, itching or hair thinning
• trouble sleeping
• a swollen thyroid gland, also known as goitre
• problems with your eyes or vision – this is more common if you have Graves’ disease
• lighter or no menstrual periods.

The diagnosis of hyperthyroidism may not be obvious at first because symptoms may be mild. See your doctor if you have any of the symptoms noted above. Your doctor will ask you questions, including whether you are taking any medicines or supplements that may affect your thyroid gland. Your doctor will usually do a physical examination and arrange blood tests which may include:

• a thyroid function test – this blood test measures your thyroid hormones (T3, T4) and thyroid stimulating hormone (TSH)
• a test for TSH receptor antibody – if you have Graves’ disease, this antibody level can be high.

If blood tests show you have an overactive thyroid, you will be referred to an endocrinologist (a specialist hormone doctor).  Sometimes other tests are needed, such as a scan of your thyroid gland.

Treatment depends on the cause of your overactive thyroid, your age, the severity of your condition, other medical conditions that may be affecting your health and your own preference. Your doctor will discuss the best treatment option with you.

Possible treatment of an overactive thyroid include:

• medicines such as carbimazole
• radioactive iodine therapy
• surgery.

If hyperthyroidism goes untreated for a long time, it may lead to severe complications, which can be avoided with treatment.

These include:

• heart problems such as atrial fibrillation or heart failure
• eye problems
• osteoporosis (brittle bones)
• a thyroid storm (fever, delirium, rapid pulse or loss of consciousness) – this is an medical emergency that needs immediate treatment.

The NZ Thyroid Support Group provides support for people to meet, talk and share information about thyroid disorders. Visit their website(external link) or contact them by phone: 09 480 2680.