What is Levothyroxine used for?

    Levothyroxine is a prescription-only medicine that treats hypothyroidism (also known as an underactive thyroid). It’s a synthetic hormone, available in either tablet or liquid form, that is designed to replenish low levels of the naturally occurring thyroid hormone.

    Key Takeaways

    What is an underactive thyroid?:

    An underactive thyroid, or hypothyroidism, happens when your thyroid gland doesn't produce enough hormones. This gland is in your neck and controls your metabolism, which is how your body turns food into energy. When it's underactive, common symptoms include weight gain, tiredness, and depression.

    Causes of an underactive thyroid:

    The most common cause is when the immune system mistakenly attacks the thyroid gland, damaging it. Another cause can be treatments for thyroid cancer or an overactive thyroid, which can sometimes result in the thyroid becoming underactive.

    Treatments for an underactive thyroid:

    The main treatment is a medication called Levothyroxine, which replaces the hormone your thyroid isn't making enough of. Sometimes, a combination therapy with other hormones is used, but it's less common. Regular blood tests help find the right dose for each person.

    What is underactive thyroid?

    Your thyroid is a small butterfly-shaped gland situated in your neck, just in front of your windpipe. Its main function is to regulate your metabolism, which is the process that converts food into energy. It does this by producing hormones called triiodothyronine (T3) and thyroxine (T4).

    If your thyroid gland is underactive, this means it doesn’t produce enough of these hormones, which then stops your body from being able to metabolise food at the correct rate. Common symptoms of an underactive thyroid include weight gain, tiredness and depression.

    Thyroid gland model

    What causes an underactive thyroid?

    There are a number of reasons that can lead to your thyroid gland underperforming, many of them relating to your immune system. There are many conditions where the immune system (usually responsible for fighting infection) mistakenly attacks your body’s own cells. When it does this to the thyroid gland, it can become damaged and unable to produce the correct hormone levels.

    Another common cause is due to previous treatment of the thyroid gland. If you’ve suffered from thyroid cancer or have had treatment or surgery to try and correct an overactive thyroid (where it essentially works overtime), then you may end up with an underactive thyroid as a side effect or result of a complication.

    Who can take Levothyroxine?

    If you’ve been diagnosed with hypothyroidism then you will likely be prescribed Levothyroxine as a first-line treatment. Finding the right dose is very much a process of trial and error to find out how much your body needs, assisted by regular blood tests to monitor the results.

    It’s important that you don’t take Levothyroxine if you have hyperthyroidism. Although the conditions sound similar, they are the exact opposite. Hypothyroidism is an underactive thyroid, whereas hyperthyroidism is an overactive thyroid. If you have hyperthyroidism then taking Levothyroxine would likely make your condition and its symptoms worse.

    What other treatments are there?

    Levothyroxine is the most common treatment for hypothyroidism and replenishes your T4 hormone. This is available as either generic Levothyroxine or the brand Eltroxin. As mentioned above, your thyroid gland produces both T3 and T4 hormones. Occasionally, a combination therapy may be used, however, this is uncommon because the evidence of its efficiency is limited and there’s a risk of side effects.

    Some people do take a T3 medicine called Liothyronine, but this is generally reserved for people who have not benefited from Levothyroxine, and it’s considerably more expensive.

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