help please switching to thyroxine from NDT - Thyroid UK

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help please switching to thyroxine from NDT


Hi there. I wanted to switch to thyroxine 2yrs ago but copped out. My T3 is too high and other problems on NDTs so I would like to switch. Can anyone give me advice on how best to do it in a gentle way? I have severe ME so am pretty fragile . I am on 2 grains on westhroid. I have been told that 1 grain =75mcg of thyroxine. I take 1 grain in the morning and 1 in the afternoon. Would it make sense to take 1/2 grain plus 1/2 tab of thyrox and then build it up to 1 tab thyrox plus 1 grain westhroid and do it like that? If so, how slowly should I do it? swithc half a grain every two weeks? 4 weeks?. Or should I just go with my GPs advice (I don't have much faith in Gps now) and drop 1 grain for 75 thyrox and then drop the other grain after a few weeks?. Any suggestions gratefully received. I'm a bit replies might be slow but I will be grateful. Thanks in advance. Wendy

12 Replies

Hi Wendy,

Sorry can't offer any advice but it is something I have been thinking of doing for a while now.

I take W.P. Thyroid and have only found a slight improvement over levo.

I switched over to NDT as my G.P. was treating by TSH and I got so fed up with the constant changing of dose that I decided to self treat with NDT.

My Doctor has now, after some research decided he will treat by symptoms, so wants me to go back to levo.

He does not know how I should change back though.

I do hope you get some replies and I watch with interest.

Good luck.


If we are already on thyroid hormone replacement we can switch from one to another easily i.e. stop one make and start another the following day.

RLC labs who make WP thyroid state that 1 grain is equivalent to 100mcg of levo.

So you may have inadvertenly been taking a little too much. You thought you were taking 150mcg when it was 200mcg.

I have never split doses as it would interrupt my life too much so one daily dose suits me fine.

If you are nervous I'd go along with your GP but 1 grain is 100mcg of levo not 75mcg.

lucylocks in reply to shaws

Hi shaws,

what concerns me and possibly Branders, it that when changing back to levo. from NDT, we will be missing the T3 in the NDT, because it will some time for the T4 in levo to build up and the T4 to convert to T3, if this is the case how long will it take for the T4 to T3 conversion.

Thank you.

Branders in reply to lucylocks

yes, that's why I was thinking of doing it slowly Lucy.

lucylocks in reply to Branders

Hi Branders,

I read somewhere (I think it was on the TPAUK forum) that the conversion chart that manufacturers of NDT give is not always accurate.

I like you thought that I may try replacing 1/2 grain of NDT with levo. and do it gradually.

There is a website were called

and the lady who runs it advises treating with a combination of NDT and levo. anyway, as she believes that the ratio of T4 and T3 in NDT does not suit everyone, so I would think when changing back to levo. the combination method should be O.K.

Have a look at the website and see what you think.

shawsAdministrator in reply to lucylocks

There is also T4 in the NDT so it shouldn't be that different. The only difference is that you will have no T3 but levo should convert to T3. T4 is inactive and it's job is to convert to T3.

lucylocks in reply to shaws

Thank you shaws,

what I can't get my head around is, although we will still have some T4 in our system from the NDT then change to levo. will the T4 in levo. convert to T3 straight away or will it need to build up before it converts?

Branders in reply to shaws

thanks Shaws. I was on 2 1/2 grains but my pulse went up to 160 and I ended up in hospital. I dropped to 2 grains but am keen to switch so that my GP can monitor me and my T3 often goes too high. Dr Myhill says 1 grain= 75mcg thyrox but I know the conversion chart says 1 grain= 100mcg. I'm thinking that since I seemed to be hypo, I should maybe take 150mcg and then increase if my bloods show I am low. Och!!! it's all so confusing when you don't trust doctors!. many thanks

shawsAdministrator in reply to Branders

It is confusing but I'd be apt to go with the Manufacturers as they have to state the actual equivalence of NDT. If your pulse went up to 160 I should think you were overdosed.

It is a problem and we seem to be swimming in the dark, i.e. trying this, trying that, increasing, decreasing. It can be never ending but I hope you soon get onto a level dose which makes you feel better.

Branders in reply to shaws

thanks Shaws. D you think it would be ok to just switch from NDTs straight to thyroxine overnight?. I know you can only give an opinion. My T3 is always at the top end of therange or above so I obviously don't have a problem converting t4 to t3....I presume. many thanks

shawsAdministrator in reply to Branders

As far as I've read, yes we can switch from one to another in equivalent dose.

I strongly disagree with the manufacturer conversion charts (as do many others). I felt horrible on an “equivalent” dose of NDT when switching from Synthroid once most of the Synthroid had left my system (somewhere around the 3 week mark). Since then I’ve been self-dosing and have titrated my dose up to 4 grains. I don’t know that I’ll need to stay on this high of a dose, but I’m taking Prilosec at the moment and this is most likely decreasing my absorption due to reduced stomach acid. I believe that most people that don’t feel well on NDT simply aren’t on a high enough dose. For others, NDT simply may not work for them.

Note that 2-4 grains is the typical NDT dose range for most patients according to MULTIPLE docs whose opinions I respect including: Dr. John Lowe, Dr. Henry Lindner, Dr. John A. Robinson, Dr. Dean Ward, Dr. Mark Starr, etc. with the "average" dose probably being somewhere around 3-3.5 grains (Dr. Mark Starr quoted this amount in his book).

I have a Word doc with hundreds of quotes from different docs based on hundreds (if not thousands) of hours of research I've done over the years and all of these docs state that 2-4 grains is the average dose range that their patients end up on when dosing by symptom relief (not blood tests) and watching for irregular pulse, blood pressure, basal temperature elevation, etc. Some need less, some need more.

To the person who mentioned - I’ve read Barb’s book and I think she did a great job with her research. One area where I’m not sure I agree with her however is that we should be trying to replicate physiological (normal) doses of what they human thyroid would make. She also suggested that thyroid labs should be taken 6-8 hours after a dose and I strongly disagree with this. You will always appear to be overmedicated if taking blood 6-8 hours after a dose of NDT or straight T3. If you wait 24 hours to test blood after a dose of NDT, you will get an accurate reflection of the FT3 level in your blood without a falsely elevated result. 2 different studies I've read have confirmed that it takes 18-24 hours for T3 levels to decrease to "normal" after dosing with anything containing T3. For example, a member on this forum stated that they always wait 24 hours after a dose of NDT for blood work. On 2 grains, their FT3 was around mid-range. On 3 grains, their FT3 was near the top of the range after 24 hours. The point being that even though T3 is processed quickly by the body, the levels will still increase over time - even after the last dose is out of your system.

As for trying to replicate physiological doses of thyroid hormone, I'm not sure this works in practice. For example, the average human thyroid might make 80-110 mcg of T4 in a day and 6-10 mcg of T3 per day (the human body likely makes somewhere around 30 mcg of T3 in a day, but most of it is from conversion of T4 and not made directly by the thyroid). Yes, in an IDEAL world where you could take a slow release pill that released a steady amount of hormone over 24 hours or have a slow drip IV infusion of thyroid meds, replacing what the body would make on its own makes perfect sense - in theory. However, when taking thyroid hormone orally once or twice a day, this is in no way similar to what the body does when it makes thyroid hormone a little bit at a time, 24 hours a day. In addition, taking thyroid hormone orally will sharply decrease TSH when the body senses a sudden influx of meds (particularly T3 containing meds) which in turn decreases T4>T3 conversion (TSH helps with this conversion). Therefore it’s sometimes necessary for us to take unnaturally high doses of thyroid medication (i.e. 4 grains of NDT = 152 mcg T4 and 36 mcg T3) to achieve symptom relief.

Also keep in mind that the body doesn’t absorb everything you take in a pill form. Absorption rates vary dramatically. Some people might only absorption 50% of what they ingest orally where as others might absorb much more.

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