Hypothyroidism Symptoms: Signs of an Underactive Thyroid and When to Get Tested

01Basics

What is hypothyroidism?

The NIDDK explains that hypothyroidism is when the thyroid gland does not make enough thyroid hormones to meet your body’s needs. The thyroid is a small, butterfly-shaped gland in the front of the neck. Its hormones control the way the body uses energy, so they affect nearly every organ, even the way the heart beats. Without enough of them, many body functions slow down.

It is common. The NIDDK says nearly 5 out of 100 Americans aged 12 and older have it, although most cases are mild or have few obvious symptoms. Women are much more likely than men to develop it, and it is more common after 60.

02Energy

Tiredness and feeling cold

Feeling extremely tired (fatigue) is the first symptom on the NHS list and on the NIDDK list. Feeling cold more than usual, or trouble tolerating cold, is another typical sign. The NIDDK also mentions joint and muscle pain and a slowed heart rate.

These symptoms are very common in everyday life. As the NIDDK points out, fatigue in particular does not necessarily mean a thyroid problem, which is why it should be checked rather than assumed.

03Weight and digestion

Weight gain and constipation

Putting on weight is a common symptom in both sources, and the NHS also lists constipation. When the body’s functions slow down, digestion can slow too.

Weight gain has many other causes, so on its own it does not point to the thyroid. If you have it together with several other symptoms in this list, it is worth mentioning to your doctor.

04Skin and hair

Skin, hair and voice changes

The NHS lists dry skin, dry hair or hair loss, and the NIDDK mentions dry skin and dry, thinning hair. The NHS also includes a croaky (hoarse) voice among the common symptoms. Our guide on hoarseness covers other reasons for a changed voice.

05Mood and thinking

Mood, concentration and other symptoms

Low mood or depression and difficulty concentrating or thinking clearly are also on the NHS list. Other symptoms described by the two sources include:

• irregular or heavy periods
• fertility problems; the NIDDK notes that women who have trouble getting pregnant often get tested for thyroid problems
• high cholesterol, to which hypothyroidism can contribute; the NIDDK advises testing for hypothyroidism if you have high cholesterol

Symptoms vary from person to person. The NHS says they may be mild, may not be easy to notice, and usually develop slowly and get worse over time; the NIDDK says you may not notice them for months or even years.

06Causes

What causes an underactive thyroid?

The most common cause is Hashimoto’s disease, an autoimmune condition in which the immune system attacks the thyroid so it cannot make enough hormone. The NHS says it is most common in women and usually starts between the ages of 30 and 50. Other causes include:

• thyroiditis, an inflammation of the thyroid, including after giving birth
• surgery to remove part or all of the thyroid, and radiation or radioactive iodine treatment
• treatment for an overactive thyroid
• some medicines, including certain heart, bipolar disorder and cancer medicines
• too little iodine in the diet, which is rare in the UK and the U.S.; the NIDDK adds that too much iodine can also cause it
• congenital hypothyroidism in babies, which is why most newborns are tested

You are more likely to have it if others in your family have had a thyroid condition, if you have had a thyroid problem before or were pregnant in the past 6 months, or if you have conditions such as celiac disease, type 1 or type 2 diabetes, rheumatoid arthritis or lupus.

07Testing

Why a symptom list cannot diagnose it: blood tests

The NIDDK is clear that a hypothyroidism diagnosis cannot be based on symptoms alone, because many of them are the same as those of other diseases. The NHS advises seeing a GP if you think you might have an underactive thyroid, because the symptoms can have other causes but are important to check.

The doctor will ask about your symptoms, about thyroid or autoimmune conditions in your family and about recent pregnancy, and may examine your neck for a swollen thyroid. Blood tests measure thyroid-stimulating hormone (TSH) and thyroxine (T4). Further thyroid blood tests or imaging may be used to confirm the diagnosis and find its cause.

Before the appointment, it helps to write down when each symptom started and how it has changed, the medicines and supplements you take (including any with iodine), and the results of earlier blood tests. This list is for the conversation with your doctor; it does not score or diagnose anything.

08Treatment

Treatment, food and follow-up

Hypothyroidism is usually treated with tablets that replace the thyroid hormone your body cannot make. The NHS says you will usually need them for the rest of your life and should be able to live a normal life. The NIDDK says a blood test is done about 6 to 8 weeks after starting, the dose is adjusted if needed, and once the right dose is found the test is usually repeated after 6 months and then once a year. Never stop the medicine without talking to your doctor; the wrong dose can cause side effects, and too much can cause serious problems such as atrial fibrillation or osteoporosis.

Diet does not replace hormone treatment. The NIDDK notes that people with Hashimoto’s disease may be sensitive to iodine: large amounts from seaweed such as kelp or dulse, or from iodine supplements, may cause or worsen hypothyroidism. Ask your care team which foods to limit and whether any supplement or cough syrup contains iodine. Our guide on diet for hypothyroidism has more on eating well with the condition. Once you have a diagnosis and treatment, our nutrition practice in Bilbao can help adults with healthy eating habits (consultations are in Spanish).

If symptoms persist during treatment, tell your doctor rather than changing the dose yourself: the dose may need adjusting, or another cause may need looking at.

09Sources

Where the sources differ

Who is most affected. The NHS says Hashimoto’s disease usually starts between 30 and 50; the NIDDK says hypothyroidism is more common in people older than 60. These describe different things (the main cause and the condition as a whole), and both agree it is much more common in women.

Symptom lists. The NHS includes constipation, difficulty concentrating and a hoarse voice. The NIDDK includes joint and muscle pain, a slowed heart rate and fertility problems. Neither list is complete or diagnostic.

Iodine. The NHS mentions only too little iodine as a rare cause. The NIDDK adds that too much iodine, from seaweed or supplements, can cause or worsen hypothyroidism in people with autoimmune thyroid disease.

10Summary

In summary

An underactive thyroid causes slow, often vague symptoms: tiredness, feeling cold, weight gain, constipation, dry skin and hair, low mood, poor concentration, a hoarse voice and period changes. Because these are common for other reasons, a blood test (TSH and T4) is needed to confirm it.

Hashimoto’s disease is the main cause. Daily hormone replacement, with regular blood tests to check the dose, usually controls it well. Diet supports health but does not replace treatment, and pregnancy needs prompt contact with your doctor.