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Potency of T3 vs T4 medications

I have read that T3 is "several times" more potent than T4, when taken for hypothyroidism.  Does anyone know specific numbers? range?  For example, if I wanted to replace 25mcg of T4 with T3, how much T3 would that be?
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Avatar universal
I'm sorry to have created a misimpression - I have a complete thyroid, haven't had RAI, been on T4 for almost 11 months, just garden variety hypo.  My problem is that whenever I increase T4, the tachy goes nuts and I have to increase the beta-blocker, which in turn makes me need more T4 (vicious circle).  My TSH is very high, FT3 and FT4 very low normal, and my PCP wants me to keep increasing.  Meanwhile, ALL my hypo symptoms have gone.  I feel great.  The only reason I have for increasing T4 is to appease my PCP and get my labs "right". I pay with the tachy.  I hear NOTHING about people whose labs make them look sick, sick, sick, but who feel just fine.  Am I really the only one?  I suspect that people with similar labs to mine are out there walking around, feeling just fine, which is why they haven't been diagnosed, and I wonder if there is anything to diagnose considering the lack of symptoms

Anyway, the heart issues are a pain in the butt, aren't they?  I don't even know if I can expect them to eventually go away.  They seem to have settled in permanently.

Thanks so much for your comments.  

It's really interesting...here they tell you that you SHOULD take your T4 on the day of your blood work...more contradictions..
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Avatar universal
Very true statement.
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280485 tn?1249013844
I think it's mute point to ask how much T3 should be taken in relationship to T4.   There are SO many variables in that equation everyone.  For instance, Do you have a thyroid or not? How well are you PERSONALLY able to convert T4 into T3?  Are you really having a problem with conversion?  How quickly do you metabolize T3?  

I personally started out post TT with a high dose of T3 in relationship to my T4.  And my body just simply wasn't able to handle it.  I went to T4 only to see how well I could convert my own T4 into T3.  I'd never been on replacement meds prior to my TT for cancer.  I didn't feel nearly as well on T4 only, and just knew I'd not due well on T4 only for the rest of my life. I switched back but at a much higher T4 to T3 ratio.  It works well for me.  But I can only take the T3 first thing in the morning unless I want to be up all night.  *I* metabolize T3 very slowly.  I know others who can take large doses both in the morning and in the evening, not feel any adverse effects and then go straight to sleep.  It's simply a function of your body and it's ability to handle T3 as well as how well it converts it's own T4 into T3.  

I seriously don't think there is one carte blanche answer for everyone.  And I'm a poster child for any and every combo of synthetic T4/T3 med combo.  It takes time and experimentation to find YOUR right dosage.
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Avatar universal
I too have heart problems with Bradycardia and Tachycardia resulting from being born with a heart murmur (born with Rheumatic Fever).It was classified as 'innocent' until I was diagnosed with Graves...and when Hyper my Inderal was increased to a high dose.
I also have Mitral Valve and Tricuspid Valve Prolapse and Regurgitation which is evaluated every year by a Cardiologist...once again only found when I was diagnosed with Graves but prior to that...never picked up.
AJ please dont mess with T3 at the moment.
Give your body time to 'heal' from the RAI.
Take each day as it comes on the Synthroid (I am on Eutroxsig here in Australia which is the proper Thyroxin) and slowly bit by bit, your levels should come under control and the heart episodes subside.
I dont have the fast heartrate anymore, I feel good and my TSH is coming down to nearly 2.0.
Yes its a pain in the butt...yes up until 3 weeks ago I felt like giving up on it all but TIME is the secret to success here.
As hard as it is to be patient, that is what is needed to get to a stage where you can function normally.
Please dont even think about T3 until you have been on the Synthroid at least 6-9 months.
They say it takes a good 12 months for levels to even out.
I was hypo 5 weeks after RAI even on the lowest dose of RAI.The Endo kept demanding 25mlc of RAI but I stood my ground and had 8mlc. I hate to think what wouldve happened if I did have 25mlc as I was T3 toxycosis when I had RAI.
Get your vitamins checked with your bloods......
Selenium, D, B12, Calcium, D, Zinc.
and slowly bit by bit you will know if you need an increase in Synthroid by your symptoms and bloods. Do it in .25mcg increments under your Doctors advise and when you go for bloods , make sure you havent taken any Synthroid that morning.
I go at 8am to get a clear even reading.
It will work out ok.....and it does get easier, I promise you.
And it wasnt my Doc who knew how to do it...it was me.
I basically educated him and we work together now and it is great.
As for the Endo, I saw her before RAI and after RAI then walked out on her as she wanted to increase my thyroxin when bloods showed T3 toxycosis !
I never went back to her.
My primary Doc works with me now and he gives me labs sheets so I can get my bloods done then call him in regards to dosage.
RAI is not an 'easy fix'....it is just as hard as getting your levels right as it was before RAI.
I had weekly appointments with my Doctor to make sure I didnt go Hyper (which I did but was picked up quick).My appointments are 3-4 weekly now.
It is a long slow road but if you tread carefully, you will get there.
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Avatar universal
We have a lot in common.

I'm also drug sensitive.  I have Wolfe-Parkinson-White syndrome, a congenital heart defect that causes tachycardia - super ventricular tachycardia (PSVT) as opposed to AFib.  The  WPW was totally under control without meds before I started taking T4.  PCP put me on 88mcg  T4 to start, and then did the fun begin!

I had to keep backing off, eventually down to 25mcg, and still the tachy raged.  So now I'm on a beta-blocker to counter that.  You're lucky your doc knew enought to do the baby steps.  It sounds like you're getting everything under control.
AJ
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Avatar universal
I'm not building the pyramid, yet...I combine and split when my dose changes.  Let's see...the blue ones are...hmmmmm.  

Isn't it amazing how "(wo)men of science" are so happy to just toss the scientific method out the door once they're in a clinical rather than a lab setting.

Oh yeah, my doc also said that they only give 5mcg to babies!!!
AJ
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