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 doesn't make enough of.

You'll 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're taking the correct dose, you'll 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 don't have any symptoms or they're 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're prescribed levothyroxine, you should take one tablet at the same time every day. It's usually recommended that you take the tablets in the morning, although some people prefer to take them at night.

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.

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 don't remember until later than this, skip the dose and take the next dose at the usual time, unless advised otherwise by your doctor.

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

If you're prescribed levothyroxine because you have an underactive thyroid, you're entitled to a medical exemption certificate. This means you don't have to pay for your prescriptions. See getting help with prescription costs for more information on this.

Side effects

Levothyroxine doesn't usually have any side effects, because the tablets simply replace a missing hormone.

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

Tell your doctor if you develop new symptoms while taking levothyroxine. You should also let them know if your symptoms get worse or don't improve.

Triiodothyronine (T3) treatment

In the UK, treatment for an underactive thyroid involving a combination of levothyroxine and a hormone called triiodothyronine (T3) isn't usually recommended, because studies have found no evidence 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).

Underactive thyroid and pregnancy

It's important for the health of you and your baby that an underactive thyroid is treated properly before you become pregnant.

Tell your GP if you're pregnant or trying to become pregnant and you have hypothyroidism. They may refer you to a specialist for treatment and monitoring during your pregnancy.

Read more about the complications of an underactive thyroid.

Page last reviewed: 11/05/2015

Next review due: 11/05/2017