Treating underactive thyroid 

An underactive thyroid (hypothyroidism) is usually treated by taking daily hormone-replacement tablets called levothyroxine.

Levothyroxine replaces the thyroxine hormone which your thyroid does not make enough of.

You will initially have regular blood tests until the correct dose of levothyroxine is reached. This can take a little while to get right.

You may start on a low dose of levothyroxine, which may be increased gradually depending on how your body responds. Some people start to feel better soon after beginning treatment, while others don't notice an improvement in their symptoms for several months

Once you are taking the correct dose, you will usually have a blood test once a year to monitor your hormone levels.

If blood tests suggest you may have an underactive thyroid, but you do not have any symptoms or they are very mild, you may not need any treatment. In these cases, your GP will usually monitor your hormone levels every few months and prescribe levothyroxine if you develop symptoms.

Taking levothyroxine

If you are prescribed levothyroxine, you should take one tablet at the same time every day.

The effectiveness of the tablets can be altered by other medications, supplements or foods, so they should be swallowed with water on an empty stomach and you should avoid eating for 30 minutes afterwards. Taking the tablets in the morning is usually recommended, although some people prefer to take them at night.

If you forget to take a dose, take it as soon as you remember if this is within a few hours of your usual time. If you do not remember until later than this, skip the dose and take the next dose at the usual time unless advised otherwise by your doctor. Do not take two doses together to make up for a missed dose.

An underactive thyroid is a lifelong condition, so you will usually need to take levothyroxine for the rest of your life.

If you are prescribed levothyroxine because you have an underactive thyroid, you are entitled to a medical exemption certificate. This means you do not have to pay for any of your prescriptions. See help with prescription costs for more information about this.

Side effects

Levothyroxine does not usually have any side effects as the tablets simply replace a missing hormone.

Side effects usually only occur if you are taking too much levothyroxine. This can cause problems including chest pain, sweating, headaches, diarrhoea and vomiting.

You should tell your doctor if you develop new symptoms while taking levothyroxine. You should also let them know if your symptoms get worse or do not improve.

Triiodothyronine (T3) treatment

In the UK, treatment for underactive thyroid involving a combination of levothyroxine and a hormone called triiodothyronine (T3) is not usually recommended because studies have found no evidence that this is more effective.

There are also concerns that taking both these hormone-replacement medications may increase your risk of serious side effects such as an irregular heartbeat (arrhythmia) and weak bones (osteoporosis).

Levothyroxine should be taken with water on an empty stomach

Underactive thyroid and pregnancy

Tell your GP if you're pregnant or are planning a pregnancy and you have an underactive thyroid. They will refer you to a specialist because there is a risk to your baby if your underactive thyroid is not treated properly during pregnancy.

See complications of an underactive thyroid for more information.

Find out how your local NHS manages hypothyroidism care

Page last reviewed: 02/07/2013

Next review due: 02/07/2015