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Liothyronine (T3)

Your body makes two main hormones, thyroxine (T4) and tri-iodothyronine (T3). Thyroxine is a pro-hormone and needs to be converted to T3. It’s T3 that your body uses for many of its functions and is therefore called the active thyroid hormone. T3 is available for your body to use as it needs it.

Liothyronine is the man-made version of tri-iodothyronine (T3) and for most people, levothyroxine is the perfect treatment and they become well.  However, there is a small group of people who see little or no improvement on levothyroxine.

There has been a lot of research into this issue over the years.  The research on whether the addition of liothyronine is helpful is inconclusive although there has been recent evidence to show that there may be a genetic difference in some people and that these people feel better with it.

The controversy surrounding liothyronine

There is a lot of controversy over the use of liothyronine and some endocrinologists agree with its use and others don’t. There have been various different guidelines across Europe and some recent ones in the UK. The recent UK guidance came about because of the exorbitant increase in the cost to the NHS.

Generally, the UK guidance, which includes the British Thyroid Association, NHS England, the Regional Medicines Optimising Committee and NICE, all state that levothyroxine should normally be prescribed and that liothyronine should not routinely be prescribed.  Unfortunately, the wording “not routinely” has been taken to mean “should not” by some clinicians and some Clinical Commissioning Groups (CCGs) (who decide on which medications can be prescribed).

CCGs are supposed to have “due regard” for the NHS England guidance and so Thyroid UK is campaigning to try to change what is happening. Read more about Thyroid UK’s T3 Campaign.

All the guidance does state that there is a cohort of patients who do not resolve all of their symptoms on levothyroxine and that they should be allowed to have a trial of liothyronine.  It can only be prescribed on a trial basis by an endocrinologist and not by GPs, as has happened for many years. The latest guidance is:

    Liothyronine acts much more quickly than levothyroxine and sometimes needs to be taken twice a day because it only lasts a few hours in the body before it runs out.  At the moment there are no licensed brands of slow-release liothyronine although there are some compounded versions from specialist pharmacies.

    There are various brands and generics (copies of brands) of liothyronine manufactured by different pharmaceutical companies. These can vary in their ingredients. Some contain lactose and therefore for people who are lactose intolerant it’s best to find a lactose-free version.  Some people are intolerant of some of the fillers and binders within the liothyronine tablet.

    For most people, there will not be any problem when taking liothyronine.  For those who do have problems with some of the ingredients, try to find out which ingredient or which generic you are having issues with.

    There are brands of tablets that are lactose-free and there are compounding pharmacies (pharmacies that make the tablet to order) that can make liothyronine tablets with very little or no fillers and binders or with fillers and binders that are less likely to cause problems.

    Read more about common thyroid medications including ingredients.

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    Date updated: 12.04.21 (V1.3)
    Review date: 11.04.22

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