Underactive thyroid: symptoms, causes and treatment

What are the symptoms of an underactive thyroid?

The thyroid sets the pace of the body's metabolism, so when it slows, a great deal slows with it. The commonest complaints are persistent tiredness, weight gain without eating more, feeling cold when other people are comfortable, constipation, dry skin, thinning or brittle hair, and a flat mood with slowed thinking.

Other features include muscle aches and cramps, a hoarse voice, puffiness around the eyes and face, heavier or irregular periods, reduced fertility, a slow pulse, and a raised cholesterol found by chance on a blood test. Some people notice a swelling at the front of the neck.

No single symptom means much on its own, and that is the difficulty. Each of these has many other explanations, and they build up gradually enough that people adapt without noticing. Because the picture is so unspecific, the condition is diagnosed on blood tests, and symptoms alone are never a reason to start or change treatment.

What causes it?

The commonest cause in adults is an autoimmune process, in which the immune system gradually damages the thyroid gland. It runs in families, and it is more frequent in women and with increasing age. It often sits alongside other autoimmune conditions, which is why a doctor will ask about them.

Treatment of an overactive thyroid is the second common route: surgery to the gland, radioactive iodine or medicines used to suppress it can all leave the thyroid underactive afterwards, sometimes years later. Radiotherapy to the neck has the same effect.

Some medicines interfere with thyroid function, and that is one reason your full medicine list matters. Thyroid inflammation after a viral illness or after pregnancy can cause a temporary underactivity that recovers, which is why not every abnormal result leads to lifelong treatment. Iodine deficiency is the main cause worldwide but is uncommon in Europe.

Babies are screened at birth, and congenital cases are managed by paediatric services rather than by any route described on this page.

Which blood tests are used?

The first test is the pituitary hormone that drives the thyroid, usually reported as TSH. When the gland is underactive, the pituitary pushes harder and that value rises. It is the most sensitive single measure and the one used for screening.

A thyroid hormone level, usually reported as free T4, is measured alongside it or after an abnormal result, because the combination distinguishes between an early, mild picture and an established one. Thyroid antibodies may be measured once, to identify the autoimmune cause; there is no reason to repeat them.

Two practical points matter more than most patients expect. Results are interpreted against the reference range of the laboratory that produced them, so compare like with like and keep the report rather than the number. And a single abnormal result in someone without symptoms is normally repeated before a diagnosis is made, because thyroid values move with illness, with pregnancy and with some medicines.

A scan is not part of routine diagnosis. It is used when there is a lump or an unusual finding on examination, which is a different question from whether the gland is underactive.

How is it treated?

Treatment replaces the missing hormone with levothyroxine, taken as one tablet a day. Levothyroxine is authorised in Malta and marketed here under brand names including Eltroxin, and our information page on /medicines/eltroxin/ describes the medicine in more detail. The dose is set by the doctor against your blood results, your age and your heart, and it is adjusted in steps rather than guessed at.

How the tablet is taken changes how much of it is absorbed, so this part is not fussiness. It is normally taken on an empty stomach with water, well before food, and kept away from calcium and iron supplements, indigestion remedies and medicines that reduce stomach acid. Coffee close to the tablet also reduces absorption. Consistency matters more than any particular hour, so pick a routine you can keep.

Improvement is gradual. Symptoms usually settle over weeks to months rather than immediately, and skin and hair are the slowest to recover, which is worth knowing so that treatment is not abandoned too early.

Do not adjust the dose yourself because you feel better or worse, and do not stop it: the underlying condition has not gone away, and levels drift back.

How is treatment monitored?

Monitoring is the treatment, in the sense that the tablet is only as good as the result it is checked against. Blood tests are repeated after a dose change and then at intervals decided by the doctor, using TSH as the main guide.

Keep a note of your current dose, the brand you take and the date of your last result. Those three items are what any doctor needs in order to continue the treatment, and they are also what makes an assessment on paper possible at all.

Pregnancy changes requirements, often early and by a significant amount, so tell a doctor as soon as you are pregnant or planning to be; this is one of the situations that belongs with a doctor who can arrange tests locally. Starting or stopping other medicines can also change what you need, which is why a new medicine is a good moment to mention the thyroid.

If tiredness persists despite results that are in range, the answer is usually to look for another cause, such as anaemia, coeliac disease, sleep problems, low mood or a vitamin deficiency, rather than to raise the dose.

When do I need medical help without delay?

Chest pain, a racing or irregular heartbeat, breathlessness at rest, fainting or collapse need immediate medical attention: an accident and emergency department, or 112 in an emergency. Levothyroxine can unmask heart problems, particularly when a dose is increased, and those symptoms are not something to sit out.

Marked drowsiness, confusion, a very low body temperature or unresponsiveness in someone known to have an underactive thyroid is a medical emergency, rare but serious, and needs the same response.

Arrange to be seen soon, rather than urgently, for a lump or swelling in the neck that is new or growing, difficulty swallowing, a persistently hoarse voice, or symptoms that are getting worse despite treatment. New symptoms during pregnancy or while planning a pregnancy also belong in this group.

One more situation worth naming: if you have not been able to take your tablets for more than a few days, say so when you seek help, because it changes the advice you will be given.

Living with an underactive thyroid

Treated properly, an underactive thyroid does not shorten life or limit what you can do, and most symptoms resolve. The condition asks for a routine rather than an effort: the same tablet, taken the same way, with a blood test at the interval your doctor sets.

Carry a note of your dose and brand when you travel, and mention the treatment whenever another medicine is started, because interactions with absorption are common and easily managed once they are known. Keep your own copy of results; laboratories and doctors change, and the sequence of your own values is more useful than any single figure.

Iodine supplements and kelp preparations are widely sold for thyroid health. They do not help in autoimmune underactivity, and too much iodine can make thyroid function worse, so they are best avoided unless a doctor advises otherwise. The same caution applies to preparations sold online as thyroid support, which are outside the authorised supply chain that the Medicines Authority oversees.

Finally, a point about expectations. Feeling well is the goal, but blood results are the instrument, and the two do not always move together week by week.