Levothyroxine v levothyroxine sodium

Hi, looking at my stash of unused thyroid medication I have only just noticed - it's only taken me 20 years!!! - that my 50mcgs of t4 are simply levothyroxine, but many of my old 25mcgs are levothyroxine sodium. Does anyone know what the chemical difference is? It is funny because I always asked for that brand of 50mcgs as I found it suited me better, it is by activism whereas I felt more symptomatic if taking the other ones which taste salty. Anyone else had that experience?

7 Replies

  • That should read made by actavis not activism!

  • I've got Almus, which are rebranded Actavis. It says levothyroxine on the box but towards the end of the leaflet it says it contains levothyroxine sodium, you might find yours is the same.

    I think thyroxine is generally provided as a sodium salt, I think it increases stability and possibly solubility.

    I've heard a lot of people say they do better with one brand over another though, could be different rates of absorption due to different fillers. Good that you've figured out which one works for you!

  • In the very early days when levothyroxine had been synthesised but was not in production, researchers found that the sodium salt gave several advantages. Since then all levothyroxine has been the sodium salt.

    In the early days when levothyroxine was widely available, some researchers investigated dextrothyroxine. Not for long as,usually, its side effects were dangerous. (There is still the tiniest level of its use in some very specific cases.) A number of years ago the packaging of most levothyroxine was changed from saying "thyroxine" to "levothyroxine" simply to avoid any possibility of confusion with dextrothyroxine - no matter how unlikely.

    At around the same time there was a sort of widespread, collective decision that for the sake of accuracy, if it is the sodium salt, well, the name should reflect that. Hence we saw very widespread use of the term "levothyroxine sodium". Later reflection suggested that unless there are actually two or more versions (e.g. there might be a possibility of producing levothyroxine potassium), forcing everyone to add the "sodium" word was heavy-handed and unnecessary. For patients they now tend to put "levothyroxine" but deep down, where accuracy may be required, they tend to put "levothyroxine sodium".

    Se we end up with a mixture of "thyroxine", "levothyroxine" and "levothyroxine sodium" as three different ways of referring to exactly the same actual substance.

    (It is not impossible that some other form of levothyroxine is made somewhere in the world. But I don't ever remember seeing it.)

    We also see that the terms "levothyroxine" and "thyroxine" are used interchangeably for the substance that goes round our bloodstreams no matter whether it came from our own thyroids, synthetic levothyroxine tablets or desiccated thyroid. Or T4! :-)


  • Wow, thanks you sure do know your stuff that's really informative. What is the pic on your name tag, I always think it looks like a pulled tooth lol!

  • A fungus! Helvella crispa. Have a look here:


    By the way, if you click on the orange "Reply"button, your response gets indented under the one you are responding to and the person gets an alert email! :-)


  • Ah, now you tell me. Thanks :-) Love the fungus!

  • :-)

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