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Thyroid UK
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Not converting?


I am self medicating with 37.5 mcg T3 (and am on 75 mcg Levothyroxine) and have found I only feel well and function when my TSH level is suppressed. My GP is not happy as he says I’m over medicated. Will taking T3 mess with my results and do the results below confirm that I am not converting? I’m thinking about having a genetic test.

TSH. 0.01 Range (0.3 - 5.6)

FT4. 5.9 Range (6.3 - 14)


5 Replies

You would need a FT4 & FT3 tests done at the same time to see if you are converting. Were these tests done whilst taking the above dose ?


Your FT4 is very low.

How do you feel?

Do you have Hashimoto's and how recently have you tested your vitamin levels

For full evaluation you ideally need TSH, FT4, FT3, TT4, TPO and TG antibodies, plus vitamin D, folate, ferritin and B12 tested

Private tests are available


Medichecks Thyroid plus ultra vitamin or Blue Horizon Thyroid plus eleven are the most popular choice. DIY finger prick test or option to pay extra for private blood draw. Both companies often have money off offers.

All thyroid tests should be done as early as possible in morning and fasting and don't take Levo in the 24 hours prior to test, T3 twelve hours before, delay and take straight after. This gives highest TSH, lowest FT4 and most consistent results



Yes, medicating T3 may alter your results in a way that most doctors will not understand.

When medicating T3, T4 levels can be low. It is the “correct” T3 result (that you haven’t posted) that is the all important as this is what gives us well being when we are not good converters but it is equally important not to overmedicate T3.

TSH levels are also often low as the pituitary gland senses the T3 in your blood stream & stops secreting TSH as thinks you have enough thyroid hormone in your body.

If you feel well & have found your “right” meds, the reason for your hypo isn’t so important. Even if you proved by testing that you are not a good converter, this will most likely fall on a doctors deaf ears.

Many doctors don’t/can’t test T3 levels & so members use private labs - link below



1 like

Ideally you should have tested TSH ft3 and ft4 whilst on levothyroxine only. This would have guided you on how well you convert t4 to t3. Any blood tests you have now will only show current levels with t3 replacement. Your TSH is is suppressed which it will be on 37.5mcg of t3, that of itself is not a problem if ft3 is in range, but you don’t know. Your ft4 is low , but if you have enough t3 this isn’t necessarily a problem. Many people on ndt have high in range ft3 and low ft4. So basically you need another blood test with TSH ft3 and ft4. It is almost impossible to get ft3 tested on the nhs so you need to go down the private blood test route. Be aware that over medication, ie ft3 and ft4 above range can cause long term damage as much as under medication can.



We would need to see your TSH, FT4 and FT3 results when you were taking Levothyroxine only to determine whether you were a poor converter. You won't have a conversion issue while you are taking T3 37.5mcg direct as no conversion is required.

Your combined 37.5mcg T3 and 75mcg Levothyroxine doses are the equivalent of 187.5mcg T4 which is a suppressive dose. It's the combined doses you are taking which suppress TSH.

Is your GP aware that you are self medicating?

I recommend you order a private thyroid test to ensure FT3 remains within range. Ideally order TSH, FT4 and FT3, but you can ordeer FT3 only if money is tight. thyroiduk.org.uk/tuk/testin...


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