Underactive thyroid (hypothyroidism)

What the thyroid does

The thyroid is a small, butterfly-shaped gland at the front of your neck. Its hormones control how your body uses energy, and they affect your breathing, heart rate, weight, digestion and mood. When it does not make enough, many of those functions slow down. An underactive thyroid is common, and it can be managed with treatment.

Symptoms

• Feeling extremely tired.
• Feeling cold more than usual.
• Putting on weight, or a puffy face.
• Constipation.
• Difficulty concentrating, low mood or depression.
• Dry skin, dry or thinning hair, or hair loss.
• A croaky (hoarse) voice, and joint or muscle pain.
• Irregular or heavy periods, or problems getting pregnant.
• A swollen neck from an enlarged thyroid (goitre).

Because the condition develops slowly, many people do not notice symptoms for months or even years. Many of these symptoms have other causes too, which is why a blood test matters more than a checklist.

Causes and who is more likely to get it

The most common cause is Hashimoto’s disease, an autoimmune condition in which the immune system attacks the thyroid. It is most common in women and usually starts between the ages of 30 and 50, but anyone can get an underactive thyroid. Other causes include:

• Inflammation of the thyroid (thyroiditis) or another thyroid condition.
• Surgery or radiotherapy to the neck or thyroid, or treatment for an overactive thyroid.
• Some medicines.
• Too little iodine in the diet, or in rare cases too much.
• Being born with it (congenital hypothyroidism).

You are more likely to have it if others in your family have had a thyroid condition. MedlinePlus also lists other conditions linked to a higher risk, including rheumatoid arthritis, Sjögren’s disease, pernicious anaemia and Turner syndrome.

How it is diagnosed

A doctor will ask about your symptoms, whether anyone in your family has had a thyroid or autoimmune condition, and whether you have been pregnant recently. They may feel your neck to see if the thyroid is swollen.

The key tests are blood tests for TSH and T4. Some people also have T3 and thyroid antibody tests, and occasionally an ultrasound or thyroid scan. The doctor may refer you to a specialist. Our guide to common blood tests explains what a thyroid panel looks at.

How it is usually treated

Treatment replaces the hormone your thyroid cannot make, usually with a tablet taken every day. Most people need it for the rest of their life to stop the symptoms coming back, and should be able to live a normal life.

Getting the dose right takes a few steps. MedlinePlus describes a blood test about 6 to 8 weeks after starting, another after each change of dose, then one at 6 months and yearly after that. Being on the wrong dose can cause side effects such as feeling sick, diarrhoea, headaches or trouble sleeping, so tell your doctor or pharmacist if you notice them. Never stop the medicine without talking to your doctor. If you have an autoimmune thyroid condition, ask which foods, supplements and medicines containing iodine to avoid.

Complications to know about

An underactive thyroid is not usually serious when it is treated properly. Left untreated, or on the wrong dose, it raises the risk of:

• Heart problems, including coronary heart disease and heart failure.
• Bone problems, including osteoporosis.
• High cholesterol. See our page on high cholesterol.
• In very rare cases, myxoedema coma, a life-threatening emergency that needs hospital treatment and is more common in older people.

Pregnancy. Tell your doctor if you are pregnant or planning a pregnancy. You will need more tests, and your dose is likely to change. Untreated, an underactive thyroid raises the chance of pre-eclampsia, premature birth and miscarriage, and can slow the baby’s growth. Treatment usually helps prevent these problems.

When to see a doctor, and when to call 998

Call 998 or go to the nearest emergency department for chest pain that feels tight or squeezing or spreads to your arms, neck or jaw, or for severe difficulty breathing. A swollen thyroid can sometimes cause trouble breathing or swallowing: get emergency help if breathing becomes hard. Myxoedema coma is rare but is an emergency.

Book an appointment if you think you might have an underactive thyroid, if your symptoms have changed while you are on treatment, or if you are planning a pregnancy. General practitioners and internal medicine doctors on medicAI work at independent facilities licensed by DHA or DoH, and can review your thyroid results with you by video and decide what comes next.