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Thyroid UK
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How much T3 to T4

I have been on 100mcg Levo for some time now and although I feel much better (iron & Vit D now much better too), I can quite shift the muscle aches and fatigue. i have purchased some T3 25mcg in the hope that it will help but despite searching for the correct T3/T4 ratio. I would like to start with a very low dose but need to know:

- how much T3 do I need to take?

- how much do I need to reduce my T4 by?

- I take the T4 Levo as soon as I wake up, when do I take the T3?

- Do I need to space out the T3?

Really grateful for any advice.

Thanks, Jlo

9 Replies

Unfortunately there is no correct ratio. Everyone is different. Starting slowly is always advisable. You may wish to start with half a tablet or even a quarter. There is some question over how much t3 is equivalent to a certain amount of t4 but 25mcg t3 is believed to be approximately equivalent to 100mcg t4. In practice this can work very differently though.

Maybe reduce to 75mcg levo and add a quarter tablet initially and then another quarter after a few days or a week or so if you are OK with it.

It really is an individual thing. Some people only need a small amount of t3, some need T3 only and some people do best on t4 only.

Sorry I couldn't be more help. Maybe someone else will have some useful reading for you.

I hope it works for you :)

Carolyn x

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Jlo, can you post your recent thyroid bloods results with the lab ref ranges as it will help members to advise on dosage.

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I was on 100 mcgs T4 before being prescribed 10mcgs T3 and dropped the T4 down to 75.

This is a low dose though........so I don't know if it will be of help for you.

Experimenting with timing is individual.I tend to take some last thing at night and some early morning on waking as that guarantees an empty stomach.

You can make adjustments as you go along depending on how you feel.

Maybe half a tablet 12 1/2 T3 and 75 T 4 would be a starter for you ?

I hope you feel better with the T3 addition.


the main thing is to not give up trying, it can be a long process finding what suits you and sometimes you may not feel your best.

I ended up on no T4 and just 30mcg of T3 taken once a day in the morning.

it just goes to show how different we all are, I finally feel ok after about 18 months of trying.

this site can help you so much, I would never have been feeling so much better without it.

good luck.

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If you can get ARMOUR THYROID,is cheaper & you donot worry about the ratio (Start low & gradually increase guided by symptoms & Temp.) T3 25 mg is TOO high to start with.

I start with 5mg tablets and divide it into 4 pieces. 1/4 daily in addition to T4 x 3days & gradually increase by 1/4 every 3 days guided by temp. & symptoms.


I don't know how much you know about people in the UK buying Armour and T3. For many, Armour is considerably more expensive than T3 (e.g. 100 tablets of each). E.g. around £15 for one source of T3 in 25mcg tablets, whereas a source of Armour is quoting about £66 to £186 for 100 tablets depending on dosage. (The Armour would also attract tax and custom clearance charges.)

I absolutely agree with you, 25mg of T3 is far, far too much. We should be talking about micrograms not milligrams.

So I rather hope you mean that you start people on 5 microgram tablets, divided into four. (Assuming you are at this point writing about T3 rather than Armour?)



Hi I am on 100 Levo and I started T3 in April. I was told not to reduce the Levo and to take half a 20 mcg T3 twice a day for two weeks. Then increase to one 20 mcg pill twice a day. If I had any heart palpitations I was told to stop taking T3 immediately.

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So confusing. Many people don't seem to know the difference between mg and mcg. To clarify T4 and T3 is usually in mcg (micrograms) and I have now introduced half. A tablet a day and will continue to monitor my pulse, temp and symptoms. Thank you to all for your advice :)


Can I ask from where you are able to buy T3?

I'm on quite a hi dose of T3 only and I am constantly made to feel guilty because my perscription costs over £300 per month. I cannot take T4 and not will I ever after my experiences with it. My fear is that I am going to be told the NHS can't afford for me to be on it. (I know some doctors won't prescribe it) so if ever I was told i couldn't have, please where can I buy it?


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