Does Synthroid contain iodine??

I'm just wondering. It was mentioned on another thread, and I can't find any info to confirm or deny.


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Yes, and here's an explanation from ThyCa's Yahoo group:

> The facts are these:
> 65% of T4 tablets are iodine.
> In the body, T4 is metabolised and, ultimately, 80% of this iodine is
> removed (deiodinated) from the organic component of the T4 and
> released into the plasma pool where it is available for re-use or
> excretion. The other 20% is released in bile and a small component of
> this may be available again before excretion. Since this iodine comes
> from the body's 'store' of T4 (not just today's tablet) it will
> continue to be around for as long as the T4 is around (gradually
> decreasing over a period of weeks).
> This means that half of the micrograms of T4 that you take end up as
> micrograms of iodine to compete with RAI for uptake. (Example: if you
> take 100mcg of T4 daily then 100mcg * 65% * 80% = 52mcg of iodine per
> day)

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Um, wow. I had no idea... so, how are you supposed to successfully achieve the goals of low-iodine for RAI when you are staying on your meds and having Thyrogen??

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Wow. This poses a very interesting conundrum for me. I take 225mcg of synthroid so by the math i'm taking in 117 mcg of iodine a day, not considering any that naturally occurs in the food I eat. This doesn't sound right; is there any way around this?

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I do believe it contains povidone, which is the source of iodine.

From memory, I think it is one of the last inactive ingredients in synthroid.

Not all manufactured levos have povidone as an inactive ingredient.

hope that helps some :)

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Jani-- you are mistaken. ALL synthetic T4 contains iodine, as it is a component of the hormone. It isn't 'free iodine', but is attached to the rest of the molecule (and might be broken down upon metabolism of the drug).
There is a picture of the chemical structure if you search thyroid hormone on Wikipedia.

Sigma - 117mcg of iodine is not a large amount (the recommended daily value for adults is 150mcg -- and "Ingestion of up to 20 times the RDA has no known side effects.")...aside from iodized salt, there is not a huge amount in the average American's diet, unless you eat a lot of seafood (which is why they started iodizing salt because iodine deficiency used to be pretty common).

I am not sure how this plays into the LID if you are having thyrogen injections rather than going off of Synthroid. It is an interesting point.

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There was a member, who was being switched from synthroid to a different manufactured levo for RAI because of the povidone, according to her account of her doctor's orders.

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additionally, humans need iodine to function, hence the low iodine and not no iodine.

it doesn't surprise me that iodine would be part of the molecular structure of levo.

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here's another wiki tidbit :)

"Iodine is required by higher animals, which use it to synthesize thyroid hormones, which contain the element. Because of this function, radioisotopes of iodine are concentrated in the thyroid gland along with nonradioactive iodine. "

another reason it makes sense that iodine is part of the levo molecular structure :))

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I've heard of a *very* small number of doctors having their patients stop their T4 medication a few days before their Thyrogen injections and RAI. On the other hand, Thyrogen has been in use for years and there aren't any major problems with people having to repeat treatment because they had iodine in their system from their T4 pill.

I know a number of nuclear medicine physicians who swear that hormone withdrawal before RAI is more effective than Thyrogen injections and staying on T4...Genzyme, the maker of Thyrogen, seems to argue there is no big difference.

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I commented on this topic on an earlier post when preparing for my LID. I looked into this on my own. I called the mail order pharmacy where I get my medications and inquired if any of my medications including L-Thyroxine (synthroid) contained iodine or red dye. I was told that the L-Thyroxine contained povidone (iodine). The pharmacy told me that Sandoz brand does not contain the povidone. I then told my Endos office about my finding. They said that's the first time they had heard that. I asked for a prescription for the Sandoz brand and it was called in for me. The same was true for my blood pressure medication Atenolol. I had that changed to Mylan brand. Both brands were available at CVS pharmacy.

I don't know how much this matters. I took both of my original medications with the first two rounds of RIA in 2009 and 2010 when I was unaware.


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Wow. I'm glad I asked. Thanks for all the info. I learn something every day from our group and love it!

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"I called the mail order pharmacy where I get my medications and inquired if any of my medications including L-Thyroxine (synthroid) contained iodine or red dye. I was told that the L-Thyroxine contained povidone (iodine)."

Yes, but this doesn't matter..the point is that ANY brand of L-thyroxine will contain iodine, by the very nature of the drug (if iodine is not part of the molecular structure, then it is not the T4 hormone anymore). If the drug is metabolized in such a way that this iodine becomes free iodine, then you'll have iodine in your system from the drug (no matter what else is in the formulation).

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Well, T4 is a molecule made up of, among other things, four iodine atoms, which your body breaks down into T3 by removing one of the iodine atoms, and so forth. So it stands to reason that those "ones" would become free iodine in your body no matter whether there was any added iodine or not. I just wonder if this is something that endos/oncos already know about and accept as far as low iodine diet prior to RAI with thyrogen. I definitely plan to ask mine.

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possibly it's the whole crux of the LID/thyrogen combo, so docs (like mine) don't even mention LID when thyrogen is used.

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obviously, the pharmacist and the doctor were not thinking of the element of iodine in the molecular structure, only the additive of iodine, as an inactive ingredient.

the doctor (and pharmacist) must not have connected the dots of the structure of levo or did not think it was pertinent to address, seeing as how the doc gave an Rx for the povidone free levo.

Arlin was taking responsible steps to try to implement as low of an iodine diet as possible, which I think is greatly commendable!

I don't know if I would have even thought to ask. :))

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a snippet:

“Thyrogen studies permit patients to continue on their thyroid replacement hormones before and during the studies.” However, patients are taking levothyroxine, which is a significant source of dietary iodine and doctors are concerned that the levothyroxine in addition to the iodine in the diet may have a negative effect on the outcome of the 131-I thyrogen scan among these patients."

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Re: "the pharmacist and the doctor were not thinking of the element of iodine in the molecular structure, only the additive of iodine, as an inactive ingredient"
Jani, I feel certain that you "hit the nail on the head". The pharmacist read the ingredients to me over the phone which included the providone.

Secondly, I happened by the endos office on my way to visit my son at the time and left a note of my finding and requesting the different brands. So, the prescription may have been called in by the NPA or the nurse. It may have bypassed the doctor completely.

Lastly, in reading the Thyroid Disease, General Information About the Low-Iodine Diet #3 "vitamin preparations have IODINE ADDED as an essential nutrient" and #4 "The problem with food colors is specific to Red dye FD&C #3"... "For medications, the best source is the Physicians (word missing on my print out - probably Desk Reference) states the ingredients." This is what prompted me to check my medications not only for the Iodine content but the Red Dye FD@C#3. Likewise, I'm may have continued to take my multiple vitamin Centrum Silver without the above resource. This article also prompted me to check into shampoos, toothpaste, etc.

Had I read Teresas response in time (today was the scan) I most likely would have gone without the synthroid for a couple of days before the scan.

This forum continues to be a learning experience for all of us and I treasure each person on it. It's good to question things - that's how we learn.

Have a good evening.

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Wow, this is really interesting! Maybe that's why my iodine level was so high before RAI. It was 117.2 and I had read somewhere online that on the LID it could get as low as the 20s (the doc confirmed this but he did say anything under 400 was acceptable). I was REALLY good about the diet- I checked everything carefully and did not eat a single thing that was not allowed- so I was surprised my level wasn't super low. Maybe it's because I stayed on Synthroid. WIsh my endo had warned me about the iodine content in Synthroid.

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Great comments. But I don't think that leaving your Synthroid off for a few days would help much, since T4 has a half-life of around 6-9 days. Right? And I would not leave mine off without consulting my doctor.

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Good point Carbo. I was feeling very hypo on the strict diet for 21 days. In fact, coming home from the hospital yesterday I had trouble concentrating on the traffic and getting home. I was very concerned. That combine with virtually no sleep (up until 4:30 am from the laxative the night before). It would not have been a good idea to stop the synthroid. If what you said is true about the half life then stopping the synthroid for me would not have lowered the iodine level anyhow and doing so may adversely affect ones abiility to drive safety to and from the hospital.


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