Micrograms and Milligrams

Hi All,

I see people writing mcg for the amount of Thyroxine, etc. they are taking.

Are people mistaking micrograms (mcg) for milligrams (mg)?

I got the following from the Internet -

One milligram is one thousandth of a gram and one thousand micrograms. A milligram is generally abbreviated as mg. One microgram is one millionth of a gram and one thousandth of a milligram. It is usually abbreviated as mcg or ug.

I take a porcine thyroid tablet daily - 162.5mgs (or milligrams), which is 162500mcgs. The equivalent of 2.5077582 grains - a measurement used for raw thyroid.

I hope this is helpful


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9 Replies

  • Thank you for the information. It's made all this so clear now.

  • It's micrograms.

    Levothyroxine is supplied and prescribed in micrograms ie 25mcg, 50mcg and 100 mcg tablets. Starting dose is usually 50mcg or sometimes 25mcg for some people which is increased to 100mcg depending on the individual. My dose presently is 75mcg.

    Previously NHS prescription Thyroxine was the same.

    Not familiar with porcine- is it on private presription?

    I have noticed that occassionally a poster has put mg as their Levothyroxine dose by mistake.



  • You might want to look up:

    ESA Position Statement on Desiccated Thyroid or Thyroid Extract



    " One grain (about 60mg) of desicated Thyroid contains about 38mcg of T4 and 9mcg of T3 . . . . . . . . . "

    X 🐥

    [ Edited by admin to fix link. ]

  • Thanks for all the information. I'm learning a lot about the subject today.

    In New Zealand and Australia (probably other countries also), pharmaceutical compounding companies import whole thyroid - porcine or bovine - and supply doctors with capsules or tablets containing T4 and T3.

  • I think we are all learning, all the time. This is an excellent forum for learning from each other and supporting each other.

    I have learned a lot from here.

    The day we stop learning will be a sad day!

    Thank you for your post.

    God Bless



  • You, or anyone else, might care to have a glance at my short document which talks about micrograms:


    You are right that people often get confused, or simply mistype, the units. But the most common mistake is to use milligrams (mg) for levothyroxine and liothyronine - which are almost always in micrograms (mcg).

    With desiccated thyroid it isn't the amount of hormone that is referred to as the potency. It is the weight of dried thyroid powder used to make the tablet (Thyroid USP for products from the USA). Only a tiny bit of that powder is actually hormone.

    Most medicines are measured in milligrams but the quantities of thyroid hormone are so tiny that is ridiculous. You do sometimes see things like 0.025 mg - mostly in USA sources. I personally find that confusing. Somehow 0.100 looks smaller than 0.05 - to my eyes (not my brain, thankfully).

    (You might see that I almost always write microgram in full. This follows official NHS advice and is intended to reduce the likelihood of mistakes, typos, confusion.)

  • Hi Helvella,

    I have learned a lot from your reply. Thank you.

    I went to the 'Special Characters' section in my word processor to copy 'µ' It could be mistaken for a 'u' so I will not use it

  • When first diagnosed I discussed the possibility of confusing hyper- and hypo- when heard, with a medical friend, who was dismissive. Yet I have a letter from a consultant (not an Endo) where that very mistake was made.

  • I too have seen a consultant's letter which confused hyperchlorhydria and hypochlorhyrdia. Worse, not just the words, but the discussion, what they said, etc.

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