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Thyroid UK
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Can someone tell me the best way to introduce t3.

Ive been on t4 for thirty years and never felt well; usual problems too numerous to mention, so i thought i would try some t3 my GP agrees with me trying it, i have had to buy it from abroad it is Cynomel from Mexico. I am taking 125mcg t4 and my recent blood test is Free t4 22.6 and TSH 0.01, i have to keep at this level because if i drop my dose my eyes flare { I had Graves and TED} I also have very low cortisol, very bad skin problems, extremely cold, huge weight gain 6st, raging tinnitus, vitiligo all my pigment has gone so i thought it was worth trying the t3 having read a lot of good reports about it i would appreciate some advice on how to start. I had my t3 tested and it came out at 5.00 which says im converting some but obviously not enough

11 Replies

i believe my husband simply subsituted 25mg of t4 for 10mg of t3 but someone else will be better versed on current ratio as cynomel is more potent than UK stuff

However since you are like my husband and had Graves and TED and Hashimotos you may well find that you will only really respond to NDT since it contains t1 t2 t3 t4 and calcitonin


Daval, it's helpful if you can include lab ref ranges when you post results as the lab values differ all over the country :)

25mcg Cynomel (T3) is roughly equivalent to 75mcg Levothyroxine (T4).

Reduce your T4 to 75mcg and cut a 25mcg Cynomel in half and take 12.5mcg daily with your T4. If you feel overmedicated (racing heart, jittery, palpitations, diarrhoea etc) cut the tablet in quarters and take 6.25mcg with T4 and a second dose of 6.25mcg 4/6 hours later. You should stay on this dose while you are feeling improvement but increase when you feel a bit 'blah' and feel the need for more.

Increase your Cynomel to 25mcg. You can take this in one dose or split into two or three doses 4/6 hours apart. It will take some experimentation to see what suits you. If 25mcg isn't sufficient you can raise it 12.5mcg increments every few weeks but you may need to decrease your T4. Do have 6 weekly blood tests to make sure you don't overmedicate and go hyper.

T3+T4 combination will keep your TSH suppressed and should improve your FT3 although your FT4 may drop as you are orally bypassing the need for T4 to T3 conversion.

Are your ferritin, vitamin D, B12 and folate good? Ferritin needs to be 70-90 and the others high in range for good absorption and conversion.




Hi Clutter, in the conversion chart 25mcg T3 is equal to 100mcg levo.



Shaws, I use the 3:1 ratio outlined in ncbi.nlm.nih.gov/pubmed/204...


Am glad your GP is supportive :) -though it's a shame he/she wasn't prepared to prescribe on the NHS...ah well. Am not clear if yur paln is to mix some T3 in with your levothyroxine or if your planning on taking T3 on it's own?

You might find reading 'Living with T3' by Paul Robinson really useful to read as it has lots of advice around T3 use alongside support with vits and minerals. It also has an approach to using T3 to support your adreanals called CT3M. He also has a website and site on facebook if you wantto look him up. Paul uses T3 only but I use combined thyroid medication ( natural dessciated thyroid) and found it a helpful read/ resource.

Using dessicated thyroid my FT4 has maintained at the top of the range ( needed for me) and FT3 is in the upper range too - never had a problem with the combined approach lowering my Ft4. T3 only medicaiton will lower your Ft4 as you are not feeding in any T4. Ft3 blood test will variy hugely once on T3 whether in combination or taken on it's own so you will not find this a very useufl guide. Paul found he had to rely on symptoms and signs -his own GP gave up testing his TSH, Ft4 or Ft3 as the results were so erractic and did not match how he was feeling.....

I don't have Graves, just classic hypothyroidism but also have extensive Vitiligo. Have you had your Vitamin D checked? You GP can do a blood test to check your level. I have to take D3 regularly as i cannot tolerate any sun -even Englsh spring sunshine burns me -so it is a case of cover up or get out of the sun. Vitamin D is important and helps your immune system to tackle autoimmune attacks on the body, as well as being essential to maintain bone density. The Vitamin D Council has very useful info on this. Symptoms of low vit D also mimic symptoms of hypothyroidism --such as fatigue, pooor restorative sleep, aches and pains.... sorry digressed but hope this is useful!


Hi Clutter, thankyou for your very helpful reply, i am listing all my blood results with lab reference ranges, Free T3 5.0 lab ref range pmol/ 3.1-6.8. Serum free T4 22.6 range pmol/L 11-25. TSH0.01 range 0.27-4.2. Ferritin 162 ug/L range15- 300. B12 468 ng/L range 180-900. Vitamin D3 R25 [OH] 39nmo/L Range 25-125 Vitamin D2 NA then it says Vit D insufficient this test was in 2012 all the rest are are very recent. I hope you can make sense of all this it gives me brain fog, I have been taking Vit D for a couple of years now started on 2000mg but doc said too much so now im taking one he has prescribed 800ius regards Daval


Sadly your GP is not up to speed on dosing for VitD. Take a look at


You will see a chart at the top of the page indicating the dose required according to your result. Divide your result 39 by 2.5 = 15.6 ng.mL - the measurement used on the chart. You will need 1000 IU's for every 10 points below 60 - the optimal result. So 4000 IU's would not be too much - and maybe even more in the beginning....

Hope you soon feel stronger....

B12 is also far too low - needs to be at the top for optimal health. Clutter has given you a good website for B12....have a good read and let us know if there is anything more we can add.....


What kind of vitamin D supplements are you taking?

If it is vitamin D2 (ergocalciferol) then you need to change it. D2 supplements are painfully slow to raise vitamin D levels - that is if they raise them at all! What you should be taking is vitamin D3 (colecalciferol).


Daval, your vitamin D is far too low. Consider a sublingual or liquid D supplement as you may not be absorbing it in capsule form.


Hi Daval, Click on the yellow Reply button underneath the post you want to answer and an email alert will be sent advising the member there is a response.

I think it will take forever to raise your vitD on 800iu. I'd take 5,000-8,000 daily for a month to fill up then drop to 2,000-5,000iu daily thereafter or until you are high in range but make sure to supplement Oct-April as light spectrum isn't good enough for skin conversion.


Hi Waveylines thankyou for your reply and all your helpful advice, i am planning to take t3 and t4 if it helps me, bit scary after all this time on t4 only but i feel so awful i think its worth a try. Ive posted blood tests to Clutter and yes i am deficient in vit d and i too burn even if the sun is behind clouds not much fun is it. Will look at Paul Robinsons book, wish id had access to a group like this back in the early eighties i would never have had RAI im sure there is another way to overcome this horrible condition, its very comforting to know if you have a question you can get so much help from all our fellow sufferers, thankyou again for taking the time to read and answer my question it is so much appreciated regards Daval


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