Underactive thyroid (hypothyroidism)
The thyroid is a small gland at the front of the neck that makes the hormones setting the pace of the whole body's metabolism.
On this page
- Symptoms that point to nothing in particular
- Why the diagnosis comes from a blood test
- Where the hormone shortage comes from
- How to take levothyroxine so that it works
- The dose is set by the test — and the treatment is not stopped
- Pregnancy and planning for it
- What happens untreated, and a rare emergency
- Online consultation
Medicines commonly prescribed for Underactive thyroid (hypothyroidism)
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: TABLET, 125 MICROGRAMSActive substance: levothyroxine sodiumManufacturer: Teva Pharma S.L.U.Prescription requiredDosage form: TABLET, 150 µgActive substance: levothyroxine sodiumPrescription requiredDosage form: TABLET, 75 mcg levothyroxine sodiumActive substance: levothyroxine sodiumManufacturer: Merck S.L.Prescription required
The thyroid is a small gland at the front of the neck that makes the hormones setting the pace of the whole body's metabolism. When they run short, the body shifts into a lower gear: the heart beats more slowly, the bowel becomes sluggish, thinking slows down. This is called hypothyroidism, and it is very common, particularly in women. Of all long-term conditions it is one of the most rewarding: the treatment is simple, inexpensive and returns people completely to their ordinary lives. The difficulty lies not in treating it but in thinking of the blood test in the first place.
Symptoms that point to nothing in particular
The defining feature of hypothyroidism is that it produces not one symptom of its own. Everything it does cause turns up in a dozen other situations, and simply in anyone who is tired.
- constant tiredness that a weekend or a holiday does not shift;
- feeling the cold when everyone around is comfortable;
- putting on weight while eating the same as before, and struggling to lose it;
- constipation;
- dry flaky skin, brittle hair, hair loss, brittle nails;
- low mood, apathy, trouble concentrating and remembering;
- a hoarse, thickened voice;
- puffiness of the face, eyelids and hands;
- heavy or irregular periods;
- aching, stiff muscles and a slow pulse.
All of it comes on slowly, over months and years, which is why it is almost never taken for an illness. People put it down to age, work, winter, stress, having had a baby, not sleeping enough — and every one of those explanations sounds plausible. That is why hypothyroidism goes unrecognised for years and is most often picked up by chance, during tests done for something else entirely.
The same feature works the other way round: having these complaints does not by itself mean you have an underactive thyroid. Tiredness and weight gain far more often have other causes. Both halves lead to the same conclusion — do not guess, check.
Why the diagnosis comes from a blood test
Hypothyroidism is diagnosed on a blood test, not on how you feel and not on an examination. No doctor can spot it by looking, and no one can feel their thyroid failing. What is needed is an ordinary blood sample of the kind any laboratory can run.
The main measurement is TSH, thyroid-stimulating hormone. It is made not by the thyroid but by the pituitary gland, and it acts as a regulator: when thyroid hormone in the blood runs low, the pituitary pushes TSH up to spur the gland on. So in hypothyroidism the TSH is raised — it is the most sensitive marker and the first to move. Alongside it, free T4, the thyroid hormone itself, is usually measured. If TSH is raised while T4 remains normal, this is called subclinical hypothyroidism: there are no clear-cut signs yet, and the doctor decides between monitoring and starting treatment depending on age, plans for pregnancy and other circumstances. To find out whether the problem is autoimmune, antibodies against thyroid tissue are also measured, and if the gland is enlarged or has nodules an ultrasound scan is arranged.
One practical point. Leave the interpretation of the numbers to your doctor: the figures on the report depend on age, on pregnancy, on the laboratory and on medicines already being taken, and "slightly outside the range" means "we keep an eye on it" in one person and "we start treatment today" in another.
Where the hormone shortage comes from
The commonest cause is autoimmune thyroiditis, also known as Hashimoto's thyroiditis. The immune system mistakes thyroid tissue for something foreign and gradually destroys it; the process runs for years, painlessly and unnoticed, until the hormone starts to fall short. It is more frequent in women and in people whose families have already had thyroid disease or other autoimmune conditions.
The other causes are less common but worth knowing, because they are predictable. Hypothyroidism follows quite naturally after removal of the thyroid or part of it, after radioactive iodine treatment and after radiotherapy to the neck — in all of these the hormone levels are monitored from the outset. Some medicines can bring it on too, among them lithium and amiodarone. A situation of its own is post-partum thyroiditis: in the year after childbirth the gland may first work too hard and then swing into underactivity, and sometimes everything settles by itself. Finally, in some people the cause is too little iodine in the diet; where that is widespread, iodised salt helps, but taking iodine supplements on your own initiative when thyroid disease is already present is not advisable — discuss it with a doctor.
How to take levothyroxine so that it works
Treatment means supplying the missing hormone as a levothyroxine tablet, an exact copy of what the gland itself produces. It is a thoroughly studied drug, it is not habit-forming, and at the right dose it causes no side effects because all it does is restore normal levels. But it is fussy about how it is taken, and most treatment failures come down to exactly that.
The tablet is taken on an empty stomach, usually in the morning, half an hour to an hour before eating, with water. If mornings are awkward, late evening works too, no sooner than several hours after the last meal. The main thing is to do it the same way every day: consistency matters more than the particular hour.
Now for the part people are rarely warned about. Levothyroxine is poorly absorbed if calcium or iron is taken close to it in time, and the same goes for indigestion remedies, antacids and some cholesterol-lowering drugs. Space these at least four hours away from the levothyroxine. Among foods, coffee, milk and soya products noticeably reduce absorption, so coffee is better half an hour to an hour after the tablet rather than with it. If you start any new medicine or supplement, tell your doctor: the timing may need separating, or the test repeating. A missed tablet is taken as soon as you remember, but if the next day has already come, do not double up.
The dose is set by the test — and the treatment is not stopped
The doctor sets the starting dose from your age, weight and the state of your heart, then checks TSH a few weeks later and adjusts. That may happen two or three times before the value settles where it should. After that the test is repeated roughly once a year, or whenever symptoms or the medication change. You will not feel better overnight: the tiredness lifting and the mental fog clearing usually takes several weeks and sometimes a couple of months.
Do not change the dose yourself. The temptation is understandable: the tiredness lingers, the weight stays on, and half a tablet more looks tempting. But too much hormone is as harmful as too little: it brings palpitations, disturbances of heart rhythm, sweating, anxiety, insomnia and shaky hands, and in the long run thinner bones and a higher risk of heart rhythm problems, especially in older people. None of that can be judged by how you feel; only the test shows it.
And the most important point: treatment for hypothyroidism is lifelong, and "a course of tablets and then stop" simply does not apply here. The tablet does not repair the gland; it replaces what the gland no longer makes. A few months after stopping, everything comes back — except that now the person is convinced the treatment did not work. Do not withdraw the drug on your own, even when you feel completely well: feeling well is precisely the sign that the dose is right.
Pregnancy and planning for it
Thyroid hormones are needed for the baby's nervous system to develop, and the baby's own gland does not start working straight away — in the early months everything comes from the mother. The requirement therefore rises during pregnancy, and the previously settled dose becomes too small.
Several things follow. If you take levothyroxine and are planning a pregnancy, mention it to your doctor in advance: it is sensible to confirm before conception that the levels are where they should be. As soon as the pregnancy is confirmed, get in touch straight away rather than waiting for the scheduled appointment — the dose almost always has to be increased, and that needs doing in the first weeks. Testing during pregnancy is more frequent than usual, and after the birth the dose goes back to the previous one, again guided by the test. Untreated hypothyroidism in pregnancy raises the risk of high blood pressure, premature birth and miscarriage, whereas correcting it promptly removes almost all of that risk. Taking levothyroxine while pregnant and while breastfeeding is safe — this is not a medicine to be stopped.
What happens untreated, and a rare emergency
Hypothyroidism left untreated for a long time hits the heart and blood vessels first: cholesterol rises, blood pressure rises, and the risk of coronary heart disease and heart failure goes up. Memory and mood suffer, and in women the cycle becomes disordered and fertility declines.
There is also a rare but deadly complication: myxoedema coma. It develops in very severe hypothyroidism, usually long neglected, most often in older people, and it is typically set off by an infection, an injury, an operation, exposure to cold or certain medicines. Signs that mean calling an ambulance (in Spain, Italy, Portugal, Poland and Ukraine the single number 112 is in use):
- sudden sluggishness, increasing drowsiness, confusion, difficulty rousing the person;
- an unusually low body temperature, especially in an older person who cannot be warmed up;
- a very slow pulse, low blood pressure, slow shallow breathing;
- a markedly puffy face with dry cold skin alongside it.
This is rare and not something to live in fear of; the point is to recognise it if it happens. That applies above all to households with an elderly relative who has thyroid disease: in them, increasing drowsiness and getting cold through in winter are not "just tired" or "just chilly" but a reason to call for help at once.
Online consultation
Hypothyroidism is managed almost entirely through blood tests and conversation, which makes it one of the most suitable subjects for remote care. An online consultation is a good place to go through vague complaints such as tiredness, feeling the cold and weight gain and to work out which tests are worth having, and equally to talk through results you already hold: what a raised TSH means, whether subclinical hypothyroidism needs treating, why the antibodies are measured.
Remotely it is also easy to settle the everyday questions that come with treatment: why things do not change immediately after starting, how to space levothyroxine away from calcium, iron or a newly prescribed drug, what to do about a missed tablet, when the next test is due, and how to act once a pregnancy is confirmed. If the doctor sees anything that calls for a face-to-face examination or urgent care, they will say so plainly.
This material is for information only and does not replace medical advice.
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