An underactive or overactive thyroid can both cause tiredness. Here's what the thyroid does, the signs to notice, and how it's checked.
Yes, it could. Both an underactive thyroid and an overactive thyroid can leave you feeling tired, though they tend to come with different sets of other symptoms. Thyroid problems are common, especially in women, and they're checked with a simple blood test, so it's one of the first things a doctor will usually think about when someone has been tired for a while.
What your thyroid does
Your thyroid is a small, butterfly-shaped gland at the front of your neck. It makes hormones that help set the pace of your body's metabolism, which affects how quickly you use energy, your heart rate, your body temperature, digestion and even how clearly you think.
The thyroid takes its cues from the pituitary gland in your brain, which releases a messenger called thyroid stimulating hormone, or TSH. When thyroid hormone levels drop, TSH rises to push the thyroid harder. When thyroid hormone levels are high, TSH falls. This feedback loop is why TSH is such a useful first test.
When the thyroid runs slow
An underactive thyroid, called hypothyroidism, is the thyroid problem most commonly linked with tiredness. When there isn't enough thyroid hormone, the body slows down.
Common signs include the following.
- Tiredness and sluggishness, often feeling slow rather than simply sleepy.
- Feeling cold when others are comfortable.
- Gradual weight gain without a clear change in eating.
- Constipation, dry skin and thinning or coarse hair.
- Low mood or trouble concentrating.
- Heavier or irregular periods.
- Puffiness around the face or a hoarse voice.
In Australia, the most common cause is an autoimmune condition called Hashimoto's thyroiditis, where the immune system gradually affects the thyroid. It often runs in families and is more common in women, after pregnancy and with age.
These changes usually creep in over months or even years. Because they're gradual, many people put them down to getting older, a demanding job or a new baby, and only realise how flat they'd been feeling once the cause is found.
When the thyroid runs fast
An overactive thyroid, called hyperthyroidism, is less common, but it can also cause tiredness. This surprises people, because everything is speeding up. The body is burning through energy, sleep is often disrupted, and muscles can feel weak.
Other signs include a racing or irregular heartbeat, feeling anxious or jittery, shaky hands, feeling hot and sweaty, weight loss despite a normal or bigger appetite, and more frequent bowel motions. Some people also notice changes in their eyes. The most common cause is another autoimmune condition, Graves' disease. Inflammation of the thyroid, which sometimes happens after pregnancy, can also cause a temporary overactive phase that's later followed by an underactive one.
How the thyroid is checked
The usual starting point is a TSH blood test. If TSH is high, it points towards an underactive thyroid. If it's low, it points towards an overactive one. Your doctor may then check free T4, sometimes free T3, and thyroid antibodies to understand the cause.
Sometimes TSH is only slightly outside the range while thyroid hormone levels are normal. This is called subclinical thyroid disease, and whether it matters depends on your symptoms, age, pregnancy plans and other results. It's often watched and retested rather than acted on straight away. Some over-the-counter products can interfere with thyroid tests, so tell your doctor about everything you take. For more on reading results in context, see understanding your blood test results.
If your thyroid is normal but you're still tired
A normal thyroid test is genuinely useful. It takes one common cause off the list and helps point attention elsewhere.
Many of the symptoms of a thyroid problem overlap with low iron, poor sleep, stress, low mood, perimenopause and blood sugar problems. It's common to look for a thyroid explanation and find the answer somewhere else. A doctor looking at the whole picture, rather than one test on its own, is more likely to find what's actually going on. You can read about the other common checks in what blood tests check for tiredness.
When to talk to a doctor
See a doctor if you've been tired for more than a few weeks, especially alongside feeling cold, weight changes, constipation, dry skin or changes to your periods. Get checked sooner if you notice a swelling or lump in your neck, difficulty swallowing, a racing or irregular heartbeat, or unexplained weight loss. It's also worth mentioning a family history of thyroid problems, or if you're pregnant, planning a pregnancy or have recently had a baby. If you have chest pain, trouble breathing or feel faint, call 000.
How UHD BioHealth can help
UHD BioHealth is a doctor-led telehealth service available across Australia. You start with a detailed online questionnaire, and an AHPRA-registered doctor reviews it within 24 hours. Where it's useful, your doctor will recommend bloodwork you can do locally, then you receive a written personalised plan with every cost listed before you pay anything, checked by a second, independent doctor, with follow-up care along the way. See what a doctor looks at for low energy.
Common questions
What are the first signs of an underactive thyroid?
Early signs are often vague, such as tiredness, feeling cold, constipation, dry skin and gradual weight gain. Because these overlap with so many other things, the only way to know is a blood test.
What blood test checks the thyroid?
The usual first test is TSH, or thyroid stimulating hormone. If it's outside the reference range, your doctor may check free T4, sometimes free T3, and thyroid antibodies to work out what's going on.
Can stress affect my thyroid?
Stress and thyroid problems can cause very similar symptoms, including tiredness, poor sleep and changes in mood and weight. Stress on its own isn't a common cause of thyroid disease, which is why testing helps tell them apart.
Running on empty by 3pm
An in-depth health questionnaire covering your history, symptoms, medications and lifestyle, read by an AHPRA-registered doctor within 24 hours. Bloodwork where it's needed, and a written plan before you pay anything.
Not ready for that yet? Get our free guide, What a doctor checks when you're always tired.
General health information only, not medical advice. Complete our questionnaire and a doctor will assess whether a consult is right for you. Individual needs and outcomes vary. In an emergency, call 000.
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