In short: Feeling tired all the time is very common and is most often linked to sleep, stress, lifestyle or mood rather than a single medical condition. However, an underactive thyroid, anaemia, diabetes and other conditions can cause ongoing tiredness, so it is worth seeing a clinician if you have been exhausted for a few weeks without a clear reason. A thyroid blood test usually starts with TSH, with further tests added only if needed.

This guide, written by a Ready Health prescribing pharmacist, explains common causes of tiredness, when a thyroid test makes sense, and what results mean, for people in Wigan, Chorley, Horwich and Bolton.

Why am I tired all the time?

Common causes include:

not enough sleep, poor-quality sleep or shift work
stress, anxiety, low mood or depression
diet, inactivity, alcohol and caffeine
hormonal changes, such as pregnancy or menopause
recovery from infections, such as glandular fever or COVID-19
side effects of medicines

Medical conditions that can cause ongoing tiredness include iron deficiency anaemia, underactive or overactive thyroid, diabetes, sleep apnoea, vitamin B12 or folate deficiency, coeliac disease, and ME/CFS.

What are the symptoms of an underactive thyroid?

An underactive thyroid (hypothyroidism) develops gradually, so symptoms are easy to put down to other things. They can include:

tiredness and low energy
feeling cold
weight gain
constipation
dry skin and dry or thinning hair
low mood and poor concentration
heavier or irregular periods
muscle aches

It is more common in women and with age, and more likely if you have another autoimmune condition, such as type 1 diabetes, or a family history of thyroid disease.

What does a thyroid blood test check?

Test	What it shows
TSH (thyroid-stimulating hormone)	The main first test. A raised TSH suggests an underactive thyroid; a low TSH suggests an overactive thyroid.
Free T4 (FT4)	Thyroxine level, used to confirm and assess an abnormal TSH.
Free T3 (FT3)	Mainly useful when an overactive thyroid is suspected.
Thyroid peroxidase (TPO) antibodies	Can show an autoimmune cause (such as Hashimoto's thyroiditis) when TSH is raised.

Thyroid results can be temporarily abnormal during or after an acute illness, and some supplements (such as biotin) can interfere with results, so mention these when you are tested.

Which other blood tests help with tiredness?

Depending on your symptoms, a clinician may suggest a full blood count, ferritin (iron stores), HbA1c (blood sugar), kidney and liver function, vitamin B12 and folate, inflammatory markers and a coeliac antibody test. Testing is most useful when it is guided by your history rather than a long panel for everyone.

What happens if my thyroid test is abnormal?

A clinician will look at your results alongside your symptoms. Mildly abnormal results are often rechecked after a few weeks or months before any decision is made. If hypothyroidism is confirmed, it is usually treated with levothyroxine, a prescription-only medicine, with regular blood tests to get the dose right. A prescriber decides whether treatment is suitable and usually shares the plan with your NHS GP for ongoing monitoring.

When should I see a doctor about tiredness?

You have felt tired for a few weeks and do not know why.
Tiredness is affecting your daily life.
You also have other symptoms, such as unexplained weight loss, night sweats, breathlessness or changes in mood.
You have been told you gasp, snort or stop breathing in your sleep.

Frequently asked questions

Can a thyroid problem make you tired?

Yes. Both underactive and overactive thyroid can cause tiredness, although most people with tiredness have normal thyroid results.

Do I need to fast for a thyroid blood test?

Fasting is not usually needed for thyroid tests alone, but it may be for some other tests. Follow the instructions you are given.

Should I test T3 as well as TSH?

Not usually. TSH is the recommended first test; FT3 is mainly helpful when an overactive thyroid is suspected.

What if my tests are normal but I'm still tired?

Normal results are reassuring. Look at sleep, stress and lifestyle, and speak to a clinician if symptoms continue or change.

Key takeaways

Tiredness is common and has many causes.
See a clinician if tiredness lasts a few weeks or comes with other symptoms.
TSH is the main first thyroid test.
Abnormal results should be interpreted by a clinician alongside symptoms.

Sources and further reading

Last reviewed: October 2026 by Shamir Patel, Independent Prescribing Pharmacist, Ready Health. This article is general information and does not replace advice from your own clinician.

Ready Health in Standish, near Wigan, Chorley, Horwich and Bolton, offers private blood tests, including thyroid tests, and private GP appointments to talk through your symptoms and results.