# What happens to synthetic T4 when you take T3?



## TheHoggle (Jan 12, 2015)

Hi,

I was wondering what would happen to *synthetic* T4 if you start to take T3? Does the body detect the T3 and stop converting the (or lower the conversion rate of the) T4 to T3 & use it for other purposes (e.g. RT3)? Or would it continue to convert the T4 as per normal?

Thanks,

TheHoggle


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## joplin1975 (Jul 21, 2011)

The conversion of t4 to t3 should be happening on an as-needed basis, so if you add in t3 without decreasing t4, you can run into hyper-like feelings. Or, to answer your question more directly, you'll probably have a build up of t4.


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## Lovlkn (Dec 20, 2009)

I take Synthetic T4 and T3.

When I added T3, my FT-4 increased and I needed to lower my T4 replacement dose.

Eventually my FT-4 came into 3/4 range along with my FT-3. It took several years.

Slow and deliberate dose changes is what got me to a good place.


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## TheHoggle (Jan 12, 2015)

joplin1975 said:


> The conversion of t4 to t3 should be happening on an as-needed basis, so if you add in t3 without decreasing t4, you can run into hyper-like feelings. Or, to answer your question more directly, you'll probably have a build up of t4.


Hi Joplin1975,

I have seen on other forums that the body can detect the presense of T3 and stop converting the T4 > T3. It then converts it to active and inactive RT3 as well as other hormones. Just wondering which is the case?


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## joplin1975 (Jul 21, 2011)

Yes, I think that's probably the case for lots of people. I also think that everyone metabolizes these hormones differently so I don't think there are hard and fast rules.


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## Lovlkn (Dec 20, 2009)

My theory is that once T3 is added, the body adjusts how much FT-4 hormone converts.

In my case on several occasions - FT-4 went into high range and needed to be lowered.

Eventually I was able to go back to my original T4 dose of 125mcg with the added Cytomel. My thinking is that some RT3 must have been created and it took awhile for my body to adjust but eventually it did. I have been on the same dose for 6 years now.

Prior to adding Cytomel I tried higher doses of T4 only hormone to try and get my FT-3 up but my conversion was not sufficient. I also gave Selenium a short trial and it did increase my FT-3 slightly. I wish I would have given it more time - I was impatient and made my final switch over to adding Cytomel.


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## ssMarilyn (Nov 15, 2013)

*I tried Cytomel once. I took the smallest dosage they had and CUT IT IN HALF and it still made me feel like I was on speed. It was horrible.*


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