Thyroid UK
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Levothyroxine (Levothyroxine Sodium)

Hi. Today I was told by my doctor that I have hypothyroidism and he has given me a prescription for Levothyroxine (25mil). I've been told that I will be taking this medication for the rest of my life.

I wanted to find out more about this medication,

1. What it is derived from?

2. How is a synthetic hormone manufactured?

3. Is there scientific research available?

4. Are there any long term side effects?

5. Are there natural alternatives?

Excuse the naivety here, this is all new to me.

Thanks, C

9 Replies

There are several routes for making levothyroxine. I don't think we have ever managed to get definitive information about the exact approach for any make or the raw materials. Unlike most hormones, thyroid hormones are chemically relatively simple.

There have been numerous patent applications for techniques to make levothyroxine (each one making special claims like extreme purity of the resulting substance). If you really are interested, I suggest you search these patent applications.

This is a very brief, high level view:

You can find thousands of papers on PubMed. If you are not familiar with PubMed, have a look at a recent post of mine:

I am always very wary of the word "natural". There is an alternative to synthetic levothyroxine - that is desiccated thyroid which is usually made from pig thyroid. No prescriptino desiccated thyroid product is licensed in the UK and it is very unlikely that you would get it presribed even as an unlicensed import - though a small number do.

Have a look here for what is potentially available:

Side effects is always a difficult issue. For some of us, levothyroxine seems to resolve the issues and has little or no side effects when appropriately dosed. Excess levothyroxine will often have similar effects to the symptoms of hyperthyroidism.

In time you will start to understand much, much more. You will also realise that the subject of thyroid is incredibly complicated and much is still not understood.

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Thanks Helvella. The PubMed looks like a very useful tool. Trying to understand all of this is a bit overwhelming.


Absolutely, it is overwhelming.

Don't feel it is your fault - I think everyone goes through that - quite possibly at regular intervals. Just as we get one thing sorted in our minds, something else comes along...

But it is worth putting some effort in because the medical profession is, generally, not very good at thyroid issues.


Yes I have been thinking 'Maybe its because I've burned myself out at work' or 'not eating right' or 'all those years of smoking'.

I am actually very healthy, which is why I'm so surprised. I eat well, do a physical job, gave up smoking, rarely drink!

Thanks for the advice, I'll bear it in mind.


Have you given up smoking?

There are many posts here (including some by me) relating to people who find they are hypothyroid in the months and years after giving up smoking. There is even quite a bit of research... Even one paper suggesting the levothyroxine might make giving up easier.

But never expect a medic to know or understand that, or doing anything proactive.


Yes I gave up smoking a year ago, but I still use the gum. I'm not sure if that has an effect with medication or not though.


Welcome to the forum, CTAA.

Hypothyroidism is a lifelong chronic condition requiring daily thyroid replacement for life.

Levothyroxine is synthetically produced in a laboratory. Refer to the patient information leaflet supplied with your Levothyroxine for a list of ingredients and potential side effects.

The active ingredients, T4 and T3, in Natural dessicate thyroid (NDT) are derived from whole pig thyroid glands but the other ingredients are synthetically produced and subject to the same chemical processes required to formulate all tablets. NDT isn't licensed for UK use and is rarely prescribed on the NHS.

For maximum absorption take Levothyroxine with water on an empty stomach 1 hour before, or 2 hours after, food and drink, 2 hours away from other medication and supplements, and 4 hours away from iron, calcium, vitamin D and oestrogen. It will take 7-10 days for Levothyroxine to be absorbed before it starts working and up to six weeks to feel the full impact of the dose by which time you should have felt some improvement in symptoms. Resolution of all symptoms isn't likely until you are optimally medicated which is usually when TSH is around 1.0.

You should have a follow up blood test in 6-8 weeks as your dose will almost certainly need increasing. Arrange a fasting (water only) early morning blood draw when TSH is highest. Take Levothyroxine after the blood draw.

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Thanks Clutter. I'm hoping the tablets will make a difference. It wasn't until yesterday that I noticed at how much I've changed over the past year. I'm like an empty shell right now!

I'll try and remember to fast for the blood test. I'm hoping this gets sorted out soon.


Hello CTAA,

I am also relatively newly diagnosed (a couple of weeks ago) and yes it's really confusing and there's so much confusing and sometimes conflicting information.

This forum is a great place to read, mull over ideas and share your thoughts and queries.

Some of the nicest things I have found here are that there is definitely no such thing as a silly question and that on low days there is a lot of support offered by folks who really do know how you are feeling!

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