Thyroid disease: signs, symptoms and treatments

Updated March 2025 | 5 min read
Expert contributor Associate Professor Shane Hamblin, President, Endocrine Society of Australia
Words by Beth Wallace

Around half the people with thyroid disease don’t know they have it. Here are all the different types, the symptoms to watch for and how to treat them.

Do you often feel tired, with sore muscles and you can't seem to warm up when it's cold? Or maybe you lose weight easily, feel your heart racing and swelter in summer. If this sounds like you, you may be one of more than a million Australians living with undiagnosed thyroid disease: the umbrella term for a group of disorders that affects the thyroid gland.

Anna Kelly understands the highs and lows of thyroid disease all too well. She was diagnosed with the condition when she was 16.

“I was really tired all of the time,” she says. “The doctors didn’t think I’d have an underactive thyroid as I was quite young, but it turned out I did. The doctor put me on thyroid replacement hormone straight away.”

What is the thyroid gland?

Located in the front of your neck just below your voice box (larynx), your thyroid gland produces three hormones: tri-iodothyronine (T3), thyroxine (T4) and calcitonin. The T3 and T4 hormones affect what goes on in just about every organ in your body, telling them to slow down or speed up their function as needed. These hormones help control:

• energy levels
• body temperature
• metabolism
• health of your muscles and bones
• brain development.

About one in 20 people will experience some form of thyroid dysfunction during their lives and women are five to eight times more likely than men to experience it. While there’s no scientific evidence to explain this, it may be due to the relationship between thyroid function and oestrogen.

If left untreated, thyroid disease can lead to serious health conditions. Depending on the type of thyroid disease you have, complications can include difficulty swallowing and breathing, eye and skin issues, osteoporosis, high cholesterol, high blood pressure and heart problems.

What are the different types of thyroid disease and what causes them?

Thyroid dysfunction can be caused by a number of factors, including autoimmune conditions and iodine deficiency. The result is either an underactive thyroid (hypothyroidism) or an overactive thyroid (hyperthyroidism). 

Underactive thyroid

According to Associate Professor Shane Hamblin, President of the Endocrine Society of Australia, Hashimoto’s disease is the most common cause of an underactive thyroid (hypothyroidism) in Australia.

He explains it’s an autoimmune disease that occurs when your body’s immune system attacks the thyroid gland. The result is too little T3 and T4 being released into the bloodstream, which then slows down your metabolism.

Anna has Hashimoto’s disease, but it took many years and multiple doctors to get her diagnosis.

“I switched doctors, and she was the first to tell me that I had Hashimoto’s, which was 19 years after my initial diagnosis,” she says. “Nobody had mentioned an autoimmune connection before – she was the first doctor to test my antibodies.”

Other causes of hypothyroidism are iodine deficiency (the most common cause of thyroid disease worldwide), congenital hypothyroidism (where a baby’s thyroid is underdeveloped at birth), some medications and removal of the thyroid.

Symptoms of an underactive thyroid may include:

• weight gain
• fatigue
• brain fog
• intolerance to cold
• muscle pain
• constipation
• heavier than normal periods
• headache
• dry, cool skin
• brittle hair and nails, thinning hair
• slow heart rate 
• swelling of the thyroid gland (goitre).

Overactive thyroid

Another autoimmune condition, Graves’ disease, is the most common cause of an overactive thyroid (hyperthyroidism), with women between the ages of 20 and 50 the most likely to be affected.

Graves’ disease occurs when your thyroid gland produces too much T3 and T4 hormone. It isn’t clear what triggers this autoimmune response, but it could be excessive iodine intake.

Other causes of hyperthyroidism include local inflammation (thyroiditis) or thyroid nodules – lumps on the thyroid gland that are caused by an overgrowth of thyroid cells.

Symptoms of an overactive thyroid may include:

• weight loss
• heat intolerance or sweating
• racing pulse or palpitations
• anxiety
• irritability
• diarrhoea
• muscle weakness or tremors
• sleeping difficulties
• infrequent menstrual bleeding or infertility
• bulging eyes or goitre (an enlarged thyroid gland).

The challenges of diagnosing thyroid disease

One of the reasons so many people live with an undiagnosed thyroid disorder, says Assoc Prof Hamblin, is that “symptoms can be vague and non-specific and may be interpreted as being caused by something else”.

He explains that women with an overactive thyroid, for example, may think they’re reaching menopause because they experience light, infrequent periods or stop menstruating altogether.

Likewise, someone with an underactive thyroid might blame overwork for their tiredness or assume weight gain stems from a lack of exercise or poor eating habits.

“The symptoms may be gradual in onset and can be subtle at the beginning,” he adds.

Because a lot of the symptoms and signs of thyroid disease are common to other conditions, blood tests are needed to confirm a diagnosis.

“Thyroid function tests are easy to do and will quickly rule in or rule out thyroid issues in most cases,” says Assoc Prof Hamblin.

Treatment for thyroid disease

How you manage or treat thyroid disease will depend on your personal diagnosis.

Treating an underactive thyroid

An underactive thyroid is easily treated with thyroxine or levothyroxine tablets, a type of thyroid hormone replacement therapy. “These are taken on an empty stomach and generally only once a day,” Assoc Prof Hamblin explains. “Treatment is usually lifelong.”

But it’s not a one-size-fits-all approach. For Anna, finding the right treatment has been an ongoing balancing act.

“My results have been all over the place – I’m probably a difficult case,” she says. “I think a lot of people go on tablets and their levels stabilise, but mine have been quite up and down.”

Anna found being proactive is key to managing her condition. Consulting with specialists, she discovered some dietary changes that have had a positive impact. She also charts her progress over time.

“I’ve kept a record of all of my blood tests for the past four years. It shows which tablets I was on and what the results were so that I can keep track and watch for trends. You have to be your own health advocate.”

Treating an overactive thyroid

Assoc Prof Hamblin says an overactive thyroid can be treated in three different ways: anti-thyroid drugs, surgery or radioactive iodine.

“Most people start using an anti-thyroid medication if the cause is Graves’ disease,” he says. “Treatment is needed for 12 to 18 months. In about 50% of cases, that will lead to long-term remission.”

If the overactive thyroid returns, a longer course of anti-thyroid drugs may be prescribed – potentially for the rest of your life. Otherwise, your doctor may recommend surgery to remove the thyroid, after which you would need lifelong thyroxine or levothyroxine therapy.

Depending on your circumstances, treatment for an overactive thyroid could also involve radioiodine therapy, an oral dose of radioactive iodine.

Where to find support

If you think you might have a thyroid disorder, when should you book a doctor’s appointment?

“See a doctor if symptoms are lasting longer than four weeks or if the symptoms are very intense,” Assoc Prof Hamblin advises.

If you can't see your GP face-to-face, eligible HCF members^* can access a standard GP consultation (up to 10 minutes) for a fee of $50 through our partnership with GP2U, an online video GP service. Eligible members who live in regional Australia can now access one standard 15-minute online GP consult with GP2U at no cost. Eligibility criteria apply^{^}.

To learn more about thyroid disease, go to the Australian Thyroid Foundation or Hormones Australia.

Get a second opinion

If you’re unsure about a diagnosis and would like another medical expert to give you some extra support, we’ll connect you to a network of independent, Australia-based medical specialists for a free second opinion⁺. You’ll have the chance to ask questions so you can confidently make the best decision for your health.