Feeling the cold far more than other people, tired all the time, and gaining weight without eating more can be signs of an underactive thyroid. The UK National Health Service (NHS) describes hypothyroidism as a common condition where the thyroid gland in the neck does not make enough hormones, and says it can be managed with treatment. Symptoms may be mild and hard to notice, and usually develop slowly and get worse over time. Treatment is usually levothyroxine tablets, normally taken for life. The NHS medicines page says to take it on an empty stomach 30 to 60 minutes before your first meal, any caffeinated drink or any other medicine. Here are the symptoms, diagnosis, causes, treatment, medicines that may not mix and pregnancy advice from two NHS pages.
1. Common symptoms: extreme tiredness, feeling cold more than usual, weight gain, constipation, low mood, dry skin and hair — they build slowly.
2. If you suspect it, see a GP — a blood test checks TSH and T4.
3. Levothyroxine once a day, on an empty stomach 30 to 60 minutes before food, coffee or other medicines. Usually for life, with regular blood tests for the dose.
Symptoms — NHS
| Type | What the NHS says | Worth noting (ours) |
|---|---|---|
| Tiredness | Feeling extremely tired (fatigue) | Listed first |
| Cold | Feeling cold more than usual | Fingers turning white or blue in the cold is Raynaud’s (link below) |
| Weight, bowels | Putting on weight, constipation | — |
| Thinking, mood | Difficulty concentrating or thinking clearly; low mood or depression | — |
| Skin, hair | Dry skin, dry hair or hair loss | — |
| Voice, periods | A croaky (hoarse) voice; irregular or heavy periods if you have them | — |
| Course | May be mild and not easy to notice; usually develop slowly and get worse over time | — |
Colour changes in cold fingers and toes are in Raynaud’s; reading TSH is in thyroid signals.
When to get help — NHS
| Situation | NHS advice | Worth noting (ours) |
|---|---|---|
| You think you might have an underactive thyroid | See a GP (non-urgent) | In Korea, a local clinic (internal or family medicine) |
| The symptoms are common ones | They can have other causes, but it’s important to get them checked by a GP | Don’t self-diagnose from tiredness or weight alone |
Diagnosis — NHS
| Type | What the NHS says | Worth noting (ours) |
|---|---|---|
| Questions | Your symptoms; whether anyone in your family has had a thyroid or autoimmune condition; whether you’ve recently been pregnant | — |
| Neck | The GP may examine your neck for a swollen thyroid | — |
| Blood tests | Levels of thyroid-stimulating hormone (TSH) and thyroxine (T4) | A high TSH means the thyroid is running low (thyroid signals) |
| Specialist | You may be referred for more tests | — |
Causes — NHS
| Type | What the NHS says | Worth noting (ours) |
|---|---|---|
| Main cause (UK) | Hashimoto’s disease — the immune system attacks the thyroid so it cannot make enough hormone | Autoimmune |
| Who | Hashimoto’s is most common in women and usually starts between 30 and 50; but anyone can get an underactive thyroid | — |
| Other causes | Another thyroid condition such as thyroiditis; surgery or radiotherapy around the neck or thyroid; treatment for an overactive thyroid; not enough iodine (rare in the UK); certain medicines | — |
| Family | More likely if others in your family have had a thyroid condition | — |
Treatment — NHS
Medicine replaces the thyroid hormone your body cannot make, usually levothyroxine tablets. You’ll usually need them for the rest of your life to stop symptoms returning, and you should be able to live a normal life, says the NHS. Regular blood tests check the dose; the wrong dose can cause feeling or being sick, diarrhoea, headaches or sleep problems. Talk to a GP or pharmacist about side effects.
Taking levothyroxine — NHS medicines page
| Type | What the NHS says | Worth noting (ours) |
|---|---|---|
| How often, how much | Usually once a day; the dose depends on hormone levels, other conditions and age, and may start low and rise gradually | — |
| When | On an empty stomach, 30 to 60 minutes before your first meal, any caffeinated drink such as tea or coffee, or any other medicine | Often first thing on waking (ours) |
| Same time | Try to take it at the same time each day | — |
| Swallowing | Tablets whole with a glass of water; liquid with the syringe or spoon supplied | — |
| Missed dose | Take it when you remember unless the next is nearly due — then skip it. Never take 2 doses together | For a child’s missed dose, ask a doctor or pharmacist |
| Too much | An extra dose is unlikely to cause problems, but speak to a pharmacist as soon as possible if you took more than prescribed; NHS 111 if you can’t | In Korea, a pharmacist or clinic; 119 if serious (ours) |
Side effects — NHS medicines page
| Type | What the NHS says | Worth noting (ours) |
|---|---|---|
| Common | Insomnia, headaches, feeling anxious, sweating, hair loss; most happen when the dose is too high and often ease when it’s changed | Usually no effect on driving, cycling or machines |
| Serious (rare) | Anaphylaxis (swollen throat or tongue, raised itchy rash, trouble breathing); thyroid crisis from a sudden rise in hormone (high temperature, fast or irregular heartbeat, dizziness or faintness, yellow eyes and skin) | NHS 111; in Korea, see a doctor at once or call 119 (ours) |
| May not suit | Past allergy or serious side effect; an overactive thyroid; diabetes; adrenal conditions; heart conditions | Check with a doctor or pharmacist first |
Medicines that may not mix — NHS medicines page
| Type | What the NHS says | Worth noting (ours) |
|---|---|---|
| Epilepsy | Carbamazepine, for example | — |
| Stomach acid | Omeprazole, for example; antacids and indigestion remedies | — |
| Others | Semaglutide (weight); sertraline (antidepressant); some blood pressure and heart medicines (beta blockers, digoxin) | — |
| Supplements | Calcium and iron supplements; St John’s wort; biotin (vitamin B7), which can affect thyroid tests | The page gives no time gap for iron — ask a doctor or pharmacist |
Iron deficiency anaemia, treated with iron tablets, is in iron deficiency anaemia.
If it isn’t treated — NHS
With the right treatment it’s not usually serious. Untreated, or on the wrong dose, there may be a higher risk of heart problems such as coronary heart disease and heart failure and bone problems such as osteoporosis. In very rare cases a severe underactive thyroid can lead to myxoedema coma, a life-threatening condition more common in older people, which is an emergency needing hospital treatment, says the NHS.
Planning a pregnancy or pregnant — NHS
If you have an underactive thyroid and are pregnant or planning to be, tell your GP. You’ll need further tests and your levothyroxine dose is likely to change. Untreated, it can raise the chance of pre-eclampsia, birth defects, premature birth or miscarriage, but treatment usually helps prevent these. You can usually take it while breastfeeding, checking with a pharmacist or doctor first.
Checklist
- ☐ Tiredness, feeling cold, weight gain, constipation building slowly: see a GP
- ☐ Blood test for TSH and T4
- ☐ Levothyroxine once a day, empty stomach, 30 to 60 minutes before food, coffee or other medicines
- ☐ Missed a dose: never take 2 together
- ☐ Calcium or iron supplements, acid medicines or biotin: tell your doctor or pharmacist
- ☐ Planning a pregnancy or pregnant: tell your GP — the dose changes
Questions that remain
Does feeling cold always mean a thyroid problem?
No. The NHS says these symptoms are common and can have other causes — which is why it says to get them checked. For fingers changing colour in the cold, see the Raynaud’s page.
When can I stop the tablets?
The NHS says you usually take them for life to stop symptoms returning; regular blood tests set the dose.
Can I take iron tablets too?
The NHS medicines page lists calcium and iron supplements as possibly not mixing well with levothyroxine and says to tell your doctor first. It gives no number of hours to leave between them.
Sources
- NHS — Underactive thyroid (hypothyroidism) — source (page shows: reviewed 28 April 2025, next review due 28 April 2028; checked 4 November 2026). Nine symptoms, when to see a GP, diagnosis (TSH, T4), causes (Hashimoto’s, 30 to 50, and others), treatment, risks, pregnancy. Also the NHS medicines page “Levothyroxine” — source (reviewed 6 July 2026, next review due 6 July 2029): how to take it (30 to 60 minutes), missed and extra doses, side effects, who it may not suit, medicines that may not mix.
- Not read. The British Thyroid Foundation and Thyroid UK pages; reference ranges for thyroid tests; Korean thyroid guidance.
- What we added. The “worth noting” column and the Korean care gloss.
Where to check further
- A local clinic — symptoms and thyroid blood tests.
- Your medicine leaflet or a pharmacist — what else you take with levothyroxine.
Written on 4 November 2026. The content is from the NHS; the glosses are ours.
