What causes delayed onset or offset of thyroid hormone?

We all know it takes time for thyroid hormone to act or stop acting on your tissues. Anyone know the exact reason? Is it due to binding activity or something else? I can't find a definitive answer when I read articles about it.

[galathea]

Well, i would think that this is because t4. (Levothyroxine) is an inert storage hormone. It needs to build up in your body over several weeks and when you have enough of it, in theory you start to convert it into t3 the active hormone, when you need some energy. The effect of t3 only lasts a short time. Ifx you stopped taking thyroid hormones, you would still be doing the converting of t4 into t3 for a while, until the stocks of t4 ran down.

We can only store t4 because it has no action until it is converted to t3. We cannot store t3 because. It is active and if we have too much of it zooming round we become hyperthyroid.

Does this help?

G xx

[Hidden in reply to galathea]

But why does it take so long for the hormone to stop acting on tissues for those who are hyperthyroid or over-medicated. All doctors I have been seeing to get over being over-medicated have said it will take a long time to recover, but never explain why.

[Hidden]

Hello Mary,

The time is takes a pill to work in or leave the body is determined by the half life.

The half life is the amount of time is takes to reduce a level by half.

The half-life for T3 in humans is about a day, but can be 1.5 days - 2.5 days depending on height, weight , metabolism, length of time medicated, etc, etc,

The half-life of T4 is 5-7 days so depending on your metabolism and dose it can take many weeks to wash ALL T4 out of your system as each 5-7 days the amount left would be halved.

Most people notice a distinct effect after a week of discontinuing T4 and further dimishment after another week. The remaining becomes more insignificant as the weeks go on and are harder to define.

emedicine.medscape.com/arti...

Flower

[Hidden in reply to Hidden]

I have read that article. Near the end it states that things should return to normal in 6-8 weeks. It doesn't explain why the action of returning to s normal state would take a couple of months. All I can think is that I may still be getting too much T4 even on my lower dose. I still don't sleep at all without sleep meds. This has caused my life as I knew it to stop. Others feel well in 2 weeks or 4 weeks or maybe even less. I'm here at 7 weeks with symptoms of over-medication.

[Hidden in reply to Hidden]

Hello Mary,

I am sorry to hear you are struggling so....I have had troubles with thyroid meds so sympathise hugely that you feel ...so not yourself.

I agree the excess T4 should have left your body or be in such insignificant amounts as to not cause these awful side effects. I think you may find the link below interesting.

I had been unsuccessfully medicating on Levo for 3-4 years which seemed to change "me". I felt different in my thought patterns and was experiencing weird head whooshes together with a jumpy heart and numerous other symptoms. In February this year I consulted with Dr P and added glandulars...(NT & NAX). After so many days and completely out of nowhere ....I experienced a psychotic episode that lasted 3 days & nights.

Dr P later explained about the possibility of blocked receptors clearing or excess reverse T3 which at the time was all a bit beyond me. There are several members who have reacted exceptionally badly to T4 and I think shaws advice in your previous post was good. I have added T3 and feel a lot more "grounded", although am still having a few issues but think it's other health problems interfering with meds doing their job properly. Everyone makes so much reverse T3 but when Levo is not utilised properly ...RT3 is made in excess to clear it out.

I had to instantly reduce my T4 after my bad experience as was suddenly so overmedicated proving Dr P's theory. Dr P is the only doctor I have met who would be willing and able to discuss all this.

Reverse T3 also rises with low iron or cortisol so make sure your levels are optimal....difficult when your poor adrenals are working flat out because you are so stressed through meds making you ill.

The article explains how even after excess T4 has left the body, it can take another 8-14 weeks for RT3 levels to drop.

stopthethyroidmadness.com/2...

Flower

[Hidden in reply to Hidden]

This was interesting. I guess I get frustrated because I keep reading about the half life of T4, but then a Dr will write in the same sentence that it has a much longer biological effect, but doesn't explain why.

[Hidden in reply to Hidden]

T4 lasts longer in the body but is ONLY a storage hormone that converts to the biologically active T3.

Some of us have trouble converting T3 from T4 and that is when you get a build up.

Flower

[Calluna]

Hi Mary,

Were you over-medicated on T4 only? I was over-medicated at one point - my FT4 went too high and I felt awful but my FT3 was still relatively low in range. I felt much better within a couple of days of stopping the T4 (in terms of hyper symptoms of anxiety, diarrhoea, shortness of breath) but I believe your body can convert an excess of T4 into reverse T3, which can then block the receptors, making it harder for the active T3 to do it's job. So my understanding is that it takes a while for the reverse T3 to fall so the T3 in the NDT I now take can do its job. So it takes longer for the hypo symptoms (fatigue etc) to improve.

x

[Hidden in reply to Calluna]

I was over-medicated on T4 only. 7 weeks after stopping the high dose I still have insomnia, anxiety and digestive issues. My one Dr said I could be experiencing this for quite a few more weeks. She doesn't explain why.

[SilverAvocado]

What are you taking now? Have you stopped T4 altogether or lowered your dose? If you are currently taking a lower dose, while that T4 drains out of your system over a period of weeks, as Flower described, you are also adding new medicine on top.

Imagine if you had a big vase of water, and it was leaking at the bottom. Each week half of the contents leaks out. But if you're pouring fresh water in at the top, that will be slowed down.

The thing with half lives is that it takes a long time for things to clear.

[SilverAvocado in reply to SilverAvocado]

To add to that, it takes about 6 week for your body to adjust to a new dose. If you imagine someone increasing their dose - their body has the exact correct dosage from day 1, because they don't need to wait for any medicine to clear out of their system.

But it still takes that person who is increasing 6 weeks to stabilise. I've actually felt differences even 4 months later.

These things just take time. Imagine if you started a new exercise programme. You wouldn't get changed on day 1. You're body moves slowly to adjust to change, make use of the chemicals put in front of it, and stop operating in panic mode as it will have been doing while you were over medicated.

[Hidden in reply to SilverAvocado]

Silver, I read your info and everything you've been through with your cancer. I admire your strength and appreciate you taking the time to answer my questions. I have read do much about thyroid, yet still have so many questions. I am frightened that I have felt so unwell for so long. I just want to sleep again on my own so I am not a zombie for my family. I'd like to go back to work and stop being a doctor's patient. When you go in to ask for meds to get you through the bad anxiety I feel like a failure...that I'm somehow just feeling sorry for myself.

[SilverAvocado in reply to Hidden]

Thank you for your kind words, maryd212.

One of the things that's helped me a lot is that I decided really early on my life wasn't going to be spoiled by whatever happened, just different than what I'd planned.

I don't waste time wishing things where different, I concentrate on making the best of what I've been given. I'm lucky in comparison to some.

It's hard hard work being ill, though. Please don't feel like a failure, you are working very hard. Sometimes it's not possible to do all that and also have a cheery smile. Be kind to yourself!

[Hidden in reply to SilverAvocado]

I was on 100 and lowered to 75 of levo. I skipped a few doses because I felt so awful. I function best with a TSH in the 2 ranges. I know many on here need a much lower TSH, but I'm not like that. Dr tested me at 4 weeks after stopping dose. TSH was 1.1 and Free T4 was 1.45(.8-1.7). That is just too much for me, personally. Clinically I am the picture of an over-medicated patient. I don't care if labs look normal. It's not normal for me.

[Calluna]

Hi Mary,

If you're still taking 75/day and you still have hyper symptoms I'd be tempted to stop all T4 until your symptoms calm down and then reintroduce at a lower level once you feel better and build up to where you're comfortable. I stopped all T4 and felt better quite quickly.

x

[Hidden in reply to Calluna]

Did you go hypo when you stopped?

[Calluna]

Hi Mary,

No more than usual. I had hypo symptoms throughout the time I was on T4-only. Even when my T4 went too high and TSH nearly disappeared and I felt awful with hyper symptoms, my T3 was still relatively low so I had a bizarre mix of hyper and hypo symptoms. But I certainly felt a lot better once I stopped the T4 and the hyper symptoms went away. When I restarted I just took 25 to keep me ticking over while I waited for the NDT to arrive. If you just go by how you feel you'll know when you need more again.

x

[helvella Administrator Thyroid UK]

Thyroid hormone affects the expression of genes - and so the amounts of the numerous proteins created inside cells. When hypothyroid, the cocktails of proteins and the absolute amounts being created are different to how they are in a someone who is not hypothyroid.

Over time (months or years), these differences have significant effects. And these effects do not disappear the moment there is sufficent thyroid hormone. Some will require the turnover of cells to go through a cycle.

For example, red blood cells have a typical life of 120 days. If at one point they are not being created quite right, then it can take around 120 days after correction of that issue for most of the cells to have been replaced. Other cells have lives which are much longer - and consequently turnover is much slower. (Some cells have longer lives, others have shorter.)