Hypothyroidism Symptoms: The Signs of an Underactive Thyroid, and Why Some Persist on Medication

The most common symptoms of hypothyroidism are tiredness, feeling the cold, weight gain, dry skin, thinning hair, constipation, low mood, muscle aches and trouble concentrating. Periods can become heavier or irregular, and the face can look puffy. Symptoms usually creep in over months or years, and they overlap with many other conditions, so they can't confirm the diagnosis on their own. A thyroid test can. Some people still have symptoms after treatment, even with results in range.

This guide explains what hypothyroidism is, the signs to know, what causes it in Australia, how it's diagnosed, and what to raise with your GP if you're on medication and still don't feel right.

When to get help straight away

Severe, untreated hypothyroidism can rarely lead to myxoedema coma, a medical emergency. Call 000 if someone with an underactive thyroid becomes very drowsy or confused, feels unusually cold to touch, or has a very slow heartbeat.

Call 000 for chest pain, or for palpitations that come with chest pain, breathlessness, dizziness or fainting. See a doctor urgently if palpitations last more than a few minutes or keep happening.

What is hypothyroidism?

Hypothyroidism, or an underactive thyroid, means your thyroid gland doesn't make enough thyroid hormone for your body's needs. Because thyroid hormone helps set the pace of your metabolism, too little of it slows many things down, from energy and digestion to heart rate and body temperature.

It is the most common thyroid condition in Australia, affecting around 1 in 33 Australians, according to Hormones Australia, the Endocrine Society of Australia's public information site. It is more common with age.

Common hypothyroidism symptoms

Australian health sources list similar signs. Grouped plainly, they are:

• Energy and mood: tiredness even after sleep, low mood or depression, low motivation, poor sleep.
• Body temperature and weight: feeling the cold when others don't, unexplained weight gain, fluid retention.
• Skin, hair and nails: dry, rough or cool skin, dry or thinning hair, thinning eyebrows, brittle nails, a pale look.
• Digestion: constipation.
• Muscles and joints: muscle aches, cramps and weakness, and sore joints.
• Periods and fertility: heavier or irregular periods, difficulty getting pregnant and lower libido.
• Memory and concentration: brain fog, a shorter attention span, forgetfulness.
• Voice and swelling: a hoarse or deeper voice, slower speech, a puffy face, swollen hands or ankles, and sometimes a swollen thyroid in the neck (a goitre).
• Heart and breathing: a slow heart rate and getting breathless more easily.

When researchers in Denmark compared people newly diagnosed with Hashimoto's-related hypothyroidism against matched people without thyroid disease, about 8 in 10 of those with hypothyroidism reported tiredness, about 6 in 10 dry skin and about half shortness of breath. Tiredness, hair loss and dry skin were the symptoms most strongly linked to the diagnosis. Even so, no single symptom was reliable enough to say who had it and who didn't. A large Colorado study found the same: people with an underactive thyroid reported more symptoms, but each symptom on its own was a weak guide.

Why the symptoms are easy to miss

Hypothyroidism usually develops slowly. When it comes from Hashimoto's, it can build over years, and healthdirect notes it can develop for a long time without obvious symptoms. Many of the signs, like tiredness, weight gain and low mood, are also common in people whose thyroid is fine, which is why they're so often put down to stress, age or a busy life.

Age changes the picture too. In the Danish study, people under 50 reported about six symptoms at diagnosis on average, while people aged 60 and over reported fewer than four. In the older group, only tiredness, shortness of breath and wheezing stood out. The researchers concluded that symptoms are a poor guide in older people, so testing should be considered more readily.

Palpitations, cholesterol and depression: how they connect

Heart palpitations. The classic heart sign of an underactive thyroid is a slow heart rate. Palpitations did show up among the symptoms linked to hypothyroidism in Danish research, but a racing or pounding heart is more typical of an overactive thyroid, or of a thyroid medicine dose that's too high. Either way, palpitations deserve a check with your doctor rather than a guess.

Cholesterol. In the Colorado study, cholesterol rose step by step as thyroid function fell. Australian GP guidance notes that unexplained high cholesterol can be a sign of undiagnosed hypothyroidism, and healthdirect lists high cholesterol as a complication when it isn't treated.

Depression. A 2021 review of 25 studies found a real but modest link between hypothyroidism and clinical depression, stronger when hypothyroidism was more marked. Low mood with a thyroid condition deserves attention on its own terms, not just a thyroid test.

What causes hypothyroidism in Australia

• Hashimoto's disease: the most common cause in Australia and other countries with enough iodine. The immune system gradually damages the thyroid. Our guide for people just diagnosed with Hashimoto's explains what that means.
• Thyroid surgery: removing the whole thyroid means you'll need thyroid hormone tablets, and after half is removed, some people need it too.
• Radioactive iodine or radiation: radioactive iodine given for an overactive thyroid, or radiation treatment to the head and neck.
• Some medicines: including lithium (a mood medicine), amiodarone (a heart-rhythm medicine) and some newer cancer immunotherapies. Never stop one of these yourself; your doctor will manage the thyroid alongside it.
• Thyroiditis: inflammation after a virus or after giving birth can cause an underactive thyroid that is sometimes temporary.
• Iodine deficiency: the most common cause worldwide, but not common in Australia. Since 2009, salt used in most bread here has had to be iodised.
• Rarely, the pituitary gland: if the gland that signals the thyroid isn't working, the thyroid isn't told to make enough hormone.

How hypothyroidism is diagnosed

Because symptoms are so common in people without thyroid disease, the diagnosis is made with a thyroid test, not a symptom list. The usual first step is TSH (thyroid stimulating hormone), the signal from your pituitary gland that rises when your thyroid isn't keeping up.

• High TSH and low free T4: overt hypothyroidism, which is usually treated with levothyroxine.
• High TSH and normal free T4: subclinical (mild) hypothyroidism. A mildly raised TSH settles on its own in about half of people, so it's usually repeated after six to eight weeks before deciding anything. Our guide to subclinical hypothyroidism and levothyroxine covers that decision.
• Thyroid antibodies (TPO): show whether Hashimoto's is the cause.

A normal TSH usually rules out an underactive thyroid, except when the pituitary is the problem, which is rare. Our guide to your thyroid panel explains each number.

Why some people still have symptoms on levothyroxine

For most people, levothyroxine brings their results into range and many symptoms ease. But not everyone feels fully well, and research backs that up.

A UK community study compared people on thyroxine from five general practices with matched people of the same age and sex who weren't. Among the nearly 400 who replied and had a TSH in range, about a third scored as having reduced psychological wellbeing, compared with about a quarter of the comparison group. The authors described the differences as real but not large. An online survey of more than 12,000 people with hypothyroidism, posted on the American Thyroid Association website in 2018, found a middling median satisfaction score of 5 out of 10, though people who choose to answer a survey like this may be less satisfied than average.

A 2022 expert review summed it up: levothyroxine improves quality of life but doesn't always restore it. Why isn't settled. Researchers including Ettleson and Bianco have pointed out that many people on levothyroxine have relatively lower T3 (the active hormone) than people whose thyroid works normally, and suggest this might matter for a small group. Trials of adding T3 have not shown a clear benefit overall, as a review by Jonklaas and Australian GP guidance both note, so this is something to discuss with an endocrinologist, not something to change yourself.

Results in range and still not feeling yourself is a real experience, and it's worth a proper conversation with your doctor.

What to check, and what to raise with your GP

Australian GP guidance suggests looking at a few common reasons when symptoms persist:

• The dose: it can take time to find the right one, and needs often change. A test decides, not symptoms.
• Timing and absorption: levothyroxine works best on an empty stomach with water, at least 30 minutes and preferably 60 minutes before food. Calcium, iron and other mineral supplements need to be several hours apart. Some medicines, such as reflux tablets, and bowel conditions can also reduce absorption.
• Conditions that travel with Hashimoto's: coeliac disease affects about 1 in 60 people with autoimmune thyroid disease, and about 1 in 4 people with hypothyroidism had low vitamin B12 in one review. Low iron and vitamin D are also worth asking about.
• Other causes of tiredness: sleep apnoea, pernicious anaemia (linked to low B12) and depression.

Questions you could take to your appointment: Is my dose right for me now? Could anything be affecting how I absorb my tablet? Should we check iron, B12, vitamin D or coeliac antibodies? Could something other than my thyroid explain this? Would seeing an endocrinologist help?

For more depth, read still tired with Hashimoto's and a normal TSH and when your tests are normal but you still feel unwell.

Where ThyroBase fits

ThyroBase is a daily morning and evening plant-based drink powder, a food rather than a medicine, made in Australia as everyday nutrition that sits alongside your thyroid medication, never instead of it. Both serves contain minerals, so keep them several hours away from your tablet. Here is who ThyroBase is, and is not, designed for, and how it fits with an underactive thyroid.

Frequently asked questions

What are the first signs of an underactive thyroid?

Tiredness is the most common early sign, often with feeling the cold, dry skin, constipation, weight gain or low mood. These tend to creep in slowly over months or years. Because they're also common without a thyroid problem, a thyroid test is the only way to know.

What is the most common cause of hypothyroidism in Australia?

Hashimoto's disease, an autoimmune condition where the immune system gradually damages the thyroid. Other causes include thyroid surgery, radioactive iodine, some medicines such as lithium and amiodarone, and inflammation of the thyroid after a virus or after giving birth. Iodine deficiency is the main cause worldwide but is uncommon in Australia.

Can hypothyroidism cause heart palpitations?

An underactive thyroid more typically slows the heart, but palpitations are reported by some people with hypothyroidism. A fast or pounding heart is more typical of an overactive thyroid or of a thyroid medicine dose that's too high. See your doctor about palpitations, and call 000 if they come with chest pain, breathlessness, dizziness or fainting.

Does hypothyroidism raise cholesterol?

It can. Studies show cholesterol tends to rise as thyroid function falls, and Australian GP guidance notes that unexplained high cholesterol can be a sign of undiagnosed hypothyroidism. Your doctor can check both.

Why do I still have hypothyroid symptoms on levothyroxine?

Common reasons include a dose that needs adjusting, something affecting how the tablet is absorbed, or another condition such as coeliac disease, low B12 or iron, sleep apnoea or depression. Research also shows some people don't feel fully well even with results in range, and the reasons aren't fully understood. Talk to your GP rather than changing your dose yourself.

The honest takeaway

Hypothyroidism symptoms are real but vague, they arrive slowly, and they look like a lot of other things, so a thyroid test is what tells you. Hashimoto's is the most common cause in Australia, and levothyroxine works well for most people. If you're on treatment and still don't feel right, that's common enough to be well recognised, and worth working through with your GP one possible cause at a time.

ThyroBase is a nutritional supplement and is not intended to diagnose, treat, cure, or prevent any disease. It is designed to sit alongside your thyroid medication, not replace it. This article is general information, not medical advice. Never start, stop or change a supplement or prescription medication without speaking to your doctor or pharmacist first.

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