Thyroid UK
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TSH 0.07 FT3 3.8 Endo won't increase T3

So been T3 only for 18 months. Feeling way better than when I took T4 but still sluggish/brain fog. Endo won't increase T3 from 40mcg/day because 'my TSH at 0.07 shows I am possibly overmedicated and my FT3 3.8 is within range (3.1-6.8) and FT3 measurements are very variable' (it was 3.4 6 months ago - that doesn't look very variable to me). What significance does TSH have? What are the dangers of it being 'too low'? I have no symptoms of overmedication only undermedication.

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"What significance does TSH have? What are the dangers of it being 'too low'?"

If it's too low, it will push you from being hypothyroid and into HYPERthyroid, which comes with a whole host of other symptoms.

Speaking as someone who only recently got into paying attention to test results, your TSH does look quite low and your FT3 is at the lower side of the testing range. I don't think I'd increase T3, but hopefully one of the more experienced members will come along shortly to help you better :)

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My TSH is suppressed <0.01 since 2012. I have no thyroid so I can't possibly be hyperthyroid. My FT4 and FT3 are mid-range so I am not over medicated. Low TSH is of no importance at all when FT4 and FT3 are within range.


You can only be hyperthyroid, technically speaking, if your body is pumping out too many thyroid hormones. Taking too much thyroid hormone might make you overmedicated but not hyperthyroid. And a suppressed TSH doesn't make you hyperthyroid or overmedicated in itself - only if it's suppressed and there's evidence that too much thyroid hormone is sloshing about in your system. If your FT3 is in range, there isn't excess thyroid hormone sloshing about. And if FT3 is low in range, it usually means more thyroid hormone replacement is required.

TSH is largely irrelevant once you've been diagnosed with hypothyroidism. Sadly, many doctors don't seem to know that.


loueldhen I'm not on T3 only (I take a combo of T4/T3) but my understanding is that when on any form of T3 (alone, synthetic combo or NDT) then TSH will be suppressed.

Your FT3 is very low in the range, this is the one result to keep an eye on and an above range FT3 would indicate overmedication. As you still have symptoms, I would have thought an increase in your T3 medication would be in order for you to feel well.

Have you ever had your vitamins and minerals tested - Vit D, B12, ferritin and folate? These all need to be optimal (not just in range) for thyroid hormone to work properly. If you have any deficiences they need to be addressed with supplements. If you've not had them tested then it would be an idea to ask your GP or endo, or even get them done privately through Blue Horizon.



Recent research has debunked the myths that suppressed TSH secondary to thyroid medication causes osteoporosis and atrial fibrillation. Unfortunately, the endos treating us don't keep up with new research which is why we are so often under treated "in our best interests" as my endo recently put it to me.

Two dose reductions didn't raise my TSH a jot and I refused to make a further reduction because I was feeling cold and slightly fatigued and said I wasn't prepared to feel unwell so she could be happy with my TSH and would buy meds on the internet if she insisted on reducing my prescription.

You might try self medicating another 10-20mcg to see whether symptoms improve when FT3 is higher.


TSH is NOT a thyroid hormone. Ignore your doctor who seems to go by numbers not how you feel! That is the best advice I can give, go by how you feel not numbers.


Thanks so much folks for your comments. The endo ignores the FT4 reading as irrelevant as I am taking T3. I don't know why he worries about TSH, I guess I should ask but as it took two months of phoning to get my results out of him - clearly he is very busy.

I have been very patient with him by sticking to his regime but I guess I need to challenge him either by upping my dose before my next blood test to see what happens or asking for further explanation. It seems logical to me to increase my T3 by 10 or 20 mcg to see what happens. He has offered to change me to NDT on a private prescription but clearly that has massive cost implications and as I had such issues with levo I'm reluctant to rock the boat and add anything with T4 in it.

He already thinks I'm weird because I take my T3 in one dose either during the night or very early morning because it sends me to sleep whereas he expects it to pep me up.


I think T3 is very misunderstood. :) My OH used to find that liothyronine brought down her pulse rate. So I can vouch for it having a calming rather than a stimulating effect.


When you are on T3, TSH has little or no significance. What matters is your FT3, which should be in the upper part of the range. Over range FT3 is what constitutes over medication. Thyroid cancer patients have their TSH deliberately suppressed (lower than yours) and they do OK.


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