Levothyroxine dosage and the limitations of current bioequivalence standards

This may be of interest to those of you on Levothyroxine


Precision in the dosing of levothyroxine (LT4) products is guided by sensitive TSH measurements, and is essential to optimize therapeutic outcomes and assure patient safety. FDA regulation of LT4 formulations aims to provide consistent drug content and bioavailability of the individual products approved for distribution in the US.1, 2 What is unclear at this point, however, is whether true generic interchangeability among approved products has been achieved.

14 Replies

  • This article is from 8 years ago and recommends that patients do not swap brands of levo and if they do that they should have levels checked, isnt this standard advice in this country? I know I was told this when I was first diagnosed by my gp.

  • I have been taking levo for a number of years and i did not know this untill i joined this site .

  • My sister didn't know this either, I think its still relevant even though its an old report.

  • Yes so do i there maybe new members that did'nt know this .

  • The MHRA "Teva" report says quite a bit about bio-equivalence - though still stops short of recommending wholesale changes:



  • Thank you for this Rod, it looks like the new dissolution test should have come in by now (January 2014)

  • Indeed it does. And I think it did but being sure is not very easy - the information might be somewhere!


  • wonder who will find it first ? ;-)

  • Hi flatfeet1 - so your sister is diagnosed but not you? (nor me) J :D

  • Yup, doesn't seem to count for anything though.

    How long have you been undiagnosed ?

  • No but ithings can 'run in' families but none in my family as far as I'm aware (pituitary trouble 'tho)

    I'm trying to think how long....

    I could never wake up easily - tired & 'lazy'

    strange episodes at school like fainting and shivering - about 10 years ago the shakiness was put down to 'anxiety'.

    I went to the GP with a cough & mentioned numb hands then had tests, one MRI showed a dodgy nodule, had a PT op in 2010 & more fatigue etc. the GP said it was now 'CFS/ME' - not my struggling half a thyroid!

    Even 'tho I had raised TPO antibodies, no diagnosis as TSH never quite over range (to 5.5), taking Vit D seemed to lower my TSH?? Sorting out vitamins/minerals has helped. J :D

  • Sorry Louise, have been meaning to get back to you but have had yet another stressful event which has knocked me sideways. Its crazy that your doc wont treat you with a high tsh and half a thyroid. Are you a bit like me; not wanting to be treated (yet) because it will be a whole new fight to get treated PROPERLY. eg levels below or near 1, or by symptoms, and then yet another fight if you need a different treatment other than Levo. Its all so exhausting even to think about. If only they could experience a day in our shoes. Have you thought about changing your doc ?


  • Are you saying Pituitary troubles run in your family?, have you had your FT4 checked ?

  • Sorry didn't see your replies, after 4 years it's a big effort to keep putting my case forward that my half a thyroid is struggling especially when ME/CFS mentioned, other people are dying after all, and I've seen 4 GPs at my surgery so far.

    The ENT doc at post-op said Thyroid was nothing to do with Pituitary! Yes I did have FT4 tested - click on my profile for list! Take care Jane :D

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