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Hypothyroidism (underactive thyroid)

Written by Caidr's team of doctors and pharmacists based in UK | Updated: 04.04.2022 | 3 min read

Hypothyroidism means that your thyroid gland is underactive, or not making enough thyroid hormone. You get symptoms of a slowed metabolism, which affects how you use and store energy.

This can affect multiple systems: you may gain weight, feel cold all the time, feel tired, sluggish and need to sleep more, and you may suffer coarse or dry skin and hair loss. You may be slower in your thinking, less able to concentrate and feel a bit depressed. You may have a slower or weaker pulse.

Hypothyroidism is very common, and is easily fixed once it’s been identified and medication started. It can take a few weeks to months for the medication to take full effect.

Your thyroid gland is a small gland in the front of your neck. It's a chain reaction, where your brain releases a hormone, which prompts the thyroid gland to release a hormone (called thyroid-stimulating hormone or TSH), which then produces thyroxine, also called free T4. This is the active biochemical.

How do I know if I have it?

If you are concerned about the above symptoms, discuss these in a routine appointment with your doctor. A blood test can check your thyroid function: if your free T4 is below the normal level and your TSH is high, this suggests hypothyroidism.

Some people have an enlarged thyroid gland, called a goitre. If very enlarged, this may be obvious to you, but your doctor will examine your neck for more subtle changes, and they may order a scan.

Hypothyroidism can occur in anyone, but is more common in women and those over 60. An autoimmune condition called Hashimoto’s thyroiditis is a subtype and is more likely in those aged 30 to 50, much more common in women, and likely causes a goitre. You or your close family members may suffer other autoimmune conditions, such as Type 1 diabetes or vitiligo.

You may have acquired hypothyroidism as a result of thyroid surgery or radiotherapy, in which case you are unable to produce enough thyroxine yourself.

Iodine deficiency is a common cause in some parts of the world and often causes a goitre. This is rare in the UK or other industrialised countries.

What happens after diagnosis?

Your doctor is experienced at managing hypothyroidism and will likely start you on levothyroxine tablets to boost your thyroxine level. You will have regular blood tests to adjust the dose until you are symptom-free and thyroid function levels have returned to normal. It takes time for medications to work – weeks rather than days – and levels are re-checked no sooner than two months after any changes.

Once stabilised on treatment, your doctor will check your thyroid function every six to 12 months, or sooner if symptoms return. If control is difficult or there are exceptional circumstances, your doctor may refer you for specialist management under an endocrinologist.

When should I seek urgent help?

It’s extremely rare for hypothyroidism to result in a medical emergency, if left untreated, there's a risk of myxoedema. People around you will notice profound weakness, drowsiness, confusion or psychosis, a slowing of the heart rate and a drop in body temperature. You may lose consciousness and enter a myxoedema coma, which is life-threatening. Any warning symptoms are reason to attend the emergency department for immediate treatment.

Are there any long-term effects?

You can avoid any long-term effects if you keep your thyroid levels well-controlled.

If left untreated or inadequately treated over a long period, you may suffer cardiovascular problems including heart failure and poor blood flow to your kidneys and other organs. You may also risk damage to the nerve endings in your arms and legs, called peripheral neuropathy.

If trying to conceive, it can cause fertility problems which can be reversed with optimal treatment. Hypothyroidism in pregnancy is usually under specialist guidance and levels are closely monitored, to ensure you and your baby are kept in the best health. Levothyroxine is always increased at the start of pregnancy.

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