Thyroid UK
82,856 members97,889 posts

How long does T4 take to work in the body?

I suffer from Hashimotos as recent blood tests show I have high Anti-TPO antibodies at 41,000 (<34) and due to a very high TSH of 22 back in May last year I have been initially put on 25mcg of levothyroxine. However with my TSH crawling back up again the dose has been increased to 150mcg.

My next blood test is coming up - on the 20th January - and I'm sure the results are going to be abnormal again as I've not felt much better since taking the increased dose since October. How long would it take for the T4 to lower the TSH?

My dose has been as follows:

23 May-6 June: 25mcg

7 June-21 June: 50mcg

22 June-22 September: 75mcg

23 September-7 November: 125mcg

8 November onwards: 150mcg

My blood test results for thyroid function tests are as follows:

January 2013

TSH - 0.69 (0.27-4.2)

Anti-TPO antibodies - 84,000 (<34)

May 2013

TSH - 22 (0.27-4.2)

FT4 - 10.9 (12-22)

**** I was started on Levothyroxine with the above instructed doses in place up to the 75mcg dose****

August 2013

TSH - 4 (0.27-4.2)

FT4 - Not done as TSH within range

Ferritin - 15 (30-400)

****Levothyroxine increased to 125mcg and started on iron meds****

November 2013

TSH - 4.3 (0.27-4.2)

FT4 - 15.3 (12-22)

FT3 (done privately) - 5.5 (3.1-6.8)

****Levothyroxine increased to 150mcg****

December 2013

TSH - 4.6 (0.27-4.2)

FT4 - 15.6 (12-22)

Ferritin - 21 (30-400)

Vitamin D - 43.6 (>75)

Vitamin B12 - 363 (180-900)

Folate - 4.1 (4.6-18.7)

****Levothyroxine not increased despite high TSH but put on Vitamin D meds - not started on folate/Vitamin B12 either****

I'm also considering adding Brazil nuts to my diet as they contain traces of T3 (sounds far fetched I know but this information is on a few sites that I've visited) - would they affect the overall thyroid function test result within 2 weeks or would this result not be seen as a true reflection of my thyroid function?

Thanks for your help.

Jo xxx

9 Replies

It might be a while before you find your optimum dose but hopefully you are getting near.

It is important to make sure the following are all optimal; serum iron, ferritin (70-90), folate (above 10), vitamin b12 (above 500) and Vitamin D. These are very important for your body to use the levothyroxine properly and could be part of the missing link. It would be good to get them tested so you know if you need to buy supplements. If any are below the NHS reference range your doctor should prescribe them. If they are low but in range you will probably have to but supplements yourself.

I hope it starts working for you very soon.

Carolyn x


Hi Carolyn, thanks for your reply. I've edited my question to include all blood test results done along with what the GP has done. Hope this helps.

Jo xxx


I can't see your edit. Are you able to see it? Once I can see it, I will have a look and see if there is anything in those results :D


Hi Carolyn, I'm sure I included my results in the edit. They're in there now. I think I've still had a few problems viewing and replying to posts on here.

I'm sure my T4 isn't working.


Jo xxx


Your b12, folate, ferritin and Vitamin D are all low and really need sorting out.

Hopefully if you get all these sorted out you soulful start to see some improvement :)


Maybe look at a few more websites? I cannot, in a quick search, find any that suggest Brazil nuts contain any T3. It sounds like a mistake than has been propagated.

Brazil nuts certainly contain selenium and that is a vital mineral required to produce the enzymes that process thyroid hormones - including converting T4 into T3.

So, by all means add Brazil nuts (in moderation) to your diet, but do not expect to get any additional T3 directly from them.



Hi Rod, I have included a link which the information came from:


Jo xxx


As I read it, that is simply a poorly worded sentence. It is struggling to say that the nuts contain substance(s) that help to make the enzymes that make T3. Not that they actually contain T3.

Lower down the article specifically mentions Selenium - and that is the main reason that people take Brazil nuts. In moderation!

I can quite see that it reads wrongly. To the best of my knowledge there are no plant-based sources of T4 or T3.


Hi Rod, thanks for clearing that up.

I thought it sounded too good to be true. I have an A Level in English so obviously I haven't put my knowledge to good use. Sorry!

Jo xxx


You may also like...