Endocrine

Medicines for Underactive thyroid (hypothyroidism)

A condition in which the thyroid gland does not make enough thyroid hormone, slowing the body down — reliably treated by replacing the missing hormone and adjusting it to blood tests.

Education and reference only. This explains which medicines are used and why, in plain language — it deliberately contains no doses and is not a substitute for advice from your doctor or pharmacist. Always discuss your own treatment with a qualified clinician, and check the BNF and the product labelling for prescribing detail.

Written by Meds Global Health Clinical Team · Clinically reviewed by Dr Muhammad Suffyan, MB BS, Founder & Clinical Director · Last reviewed · How we review

Quick answer

What is Underactive thyroid (hypothyroidism)?

The thyroid is a small gland in the neck that makes hormones controlling the body's metabolism. In an underactive thyroid it does not make enough, and body processes slow down, causing tiredness, weight gain, feeling cold, dry skin, constipation, low mood and sometimes a slow pulse.

  • How it is treated: Treatment replaces the hormone the thyroid is no longer making, using levothyroxine — a synthetic version of thyroxine (T4) that the body converts as needed.
  • Self-care: There is no diet that cures an underactive thyroid, but taking levothyroxine consistently at the same time each day, and keeping it apart from supplements such as iron and calcium, helps keep levels steady.
  • When to seek help: Rarely, severe untreated hypothyroidism can cause extreme drowsiness, confusion or feeling very cold and unwell, which needs urgent care.

What it is

The thyroid is a small gland in the neck that makes hormones controlling the body's metabolism. In an underactive thyroid it does not make enough, and body processes slow down, causing tiredness, weight gain, feeling cold, dry skin, constipation, low mood and sometimes a slow pulse. Symptoms come on gradually and can be vague, so the condition is often picked up on a blood test. The commonest cause in the UK is an autoimmune condition (Hashimoto's) in which the immune system gradually damages the gland; it can also follow thyroid surgery or treatment for an overactive thyroid. Diagnosis rests on blood tests measuring thyroid-stimulating hormone (TSH) from the pituitary gland together with the thyroid hormone thyroxine (T4); a raised TSH with a low T4 is the typical pattern.

How it is treated

Treatment replaces the hormone the thyroid is no longer making, using levothyroxine — a synthetic version of thyroxine (T4) that the body converts as needed. The principle is to start carefully and adjust the amount in steps, guided by how the person feels and, crucially, by repeat blood tests, aiming to bring the TSH back into the normal range; this fine-tuning is done by blood test rather than by symptoms alone. As a practical point, levothyroxine is generally taken on an empty stomach and kept apart from certain other foods, supplements and medicines that can reduce its absorption. Once the right level is established, it is checked periodically and after any change. Pregnancy is a special situation: hormone needs typically rise, so women who are pregnant or planning pregnancy should be reviewed promptly because under-treatment can affect the baby.

For this condition, these medicines

Medicine classes used for Underactive thyroid (hypothyroidism)

Each links to a full, dose-free guide — what it is, how it works, who can and cannot use it, side effects, interactions and FAQs.

Levothyroxine Endocrine The mainstay of treatment; it replaces the missing thyroid hormone thyroxine (T4) and is adjusted to bring the TSH blood test into range.

Symptom checker

Symptoms that can point to Underactive thyroid (hypothyroidism)

Underactive thyroid (hypothyroidism) can be one cause of these symptoms. Each guide explains the other possible causes and the red-flag warning signs that mean you should get urgent help:

FatigueA persistent lack of energy or overwhelming tiredness that is not relieved by rest and int…ConstipationPassing stools less often than usual, or finding them hard, dry and difficult to push out …Hair lossThinning or shedding of hair on the scalp or body that is most often a natural, gradual pa…Low moodLow mood means feeling sad, flat or down for a period of time, which can be a normal react…Memory problemsMemory problems mean finding it harder to remember things or think clearly, which can have…Weight gainWeight gain is an increase in body weight, which is usually due to diet and activity but c…SnoringA rattling, snorting or whistling noise made when breathing during sleep as air passes a p…Excessive daytime sleepinessA persistent struggle to stay awake during the day — nodding off, fighting heavy eyelids o…Hoarse voiceA rough, raspy, weak or croaky change in the voice from irritation, swelling or strain of …Cold or discoloured hands and feetHands or feet that feel persistently cold or change colour — turning white, blue or red — …Muscle weaknessA genuine loss of strength in one or more muscles — different from simply feeling tired — …Muscle crampsSudden, painful, involuntary tightening of a muscle — usually a harmless, short-lived spas…Swollen tongue or lipsSwelling of the tongue, lips or mouth that can be a harmless reaction or a sign of an alle…Pale skinSkin that looks paler than usual, sometimes with pale lips, gums or inner eyelids, which c…Difficulty concentrating / brain fogA frustrating sense of being mentally cloudy, forgetful or unable to focus, most often cau…Feeling cold all the timeFeeling cold when others are comfortable, or being unusually sensitive to cold, which is o…Irregular periodsPeriods that come unpredictably, too often, too rarely, or with cycles that vary in length…Dry, flaky skinSkin that feels rough, tight, flaky or scaly because it is short of moisture — usually dow…Brittle or changing nailsNails that split, peel, ridge, crumble or change colour and shape — often simply from age,…

By active ingredient

Specific medicines used for Underactive thyroid (hypothyroidism)

Dose-free guides to individual active ingredients used in underactive thyroid (hypothyroidism) — what each is, how it works, how to take it, and its advantages and disadvantages:

LiothyronineA fast-acting thyroid hormone (T3) used in specific underactive-thyroid situations rather …Iodine supplementA supplement that provides iodine, the mineral the thyroid uses to make its hormones, used…LevothyroxineThe standard treatment for an underactive thyroid — a daily tablet that simply replaces th…

Beyond medication

Lifestyle and self-care

There is no diet that cures an underactive thyroid, but taking levothyroxine consistently at the same time each day, and keeping it apart from supplements such as iron and calcium, helps keep levels steady.

When to get help

When to see a doctor

Rarely, severe untreated hypothyroidism can cause extreme drowsiness, confusion or feeling very cold and unwell, which needs urgent care. More commonly, persistent tiredness, low mood or symptoms that return should be discussed with your GP, who can check a blood test and adjust treatment.

999Emergency — call 999 or go to A&E
111Urgent advice — call NHS 111 or use 111 online
GPNon-urgent — see your GP or pharmacist

Not sure how urgent it is? It is always OK to call NHS 111 for advice, day or night.

Answers

Underactive thyroid (hypothyroidism): frequently asked questions

What medicine is used for an underactive thyroid?

The standard treatment is levothyroxine, which replaces the thyroid hormone your body is no longer making enough of. For most people it fully controls the condition. The amount is adjusted using blood tests so that your thyroid-stimulating hormone (TSH) returns to the normal range.

Do I have to take levothyroxine for life?

Usually, yes. Most causes of an underactive thyroid are permanent, so the hormone needs replacing long-term. Because it simply restores what your body should be making, it is safe to continue indefinitely when monitored, and you should not stop without medical advice.

Why does my dose keep changing?

The aim is to keep your blood tests in the right range, and the amount needed can change over time, after illness, with weight changes, with some other medicines, and especially in pregnancy. Your prescriber adjusts it in steps and rechecks a blood test to confirm the level is right.

Why am I told to take it on an empty stomach?

Levothyroxine is absorbed best when the stomach is empty, and some foods, drinks and supplements — such as iron and calcium — can reduce how much your body takes up. Taking it consistently and apart from these helps keep your thyroid levels steady.

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Sources

Where this is drawn from

  • NICE NG145: Thyroid disease: assessment and management.
  • NICE CKS: Underactive thyroid (hypothyroidism).

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