Thyroid UK
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too much levothyroxine

hello guys,

i know that much of you guys have no thyroid working due inumerous factors, my question here is is it possible to abnourmous quantities of levo might harm or even destroy the healthy thyroid gland, lets suppose that i have hypothyroidism and i still have some part of my thyroid working, is it possible to destroy my part of my working gland destroyd due exagerated dose of levo...sorry im not english native, but i think u got the point of my questio...

tx in advance

7 Replies


Taking excessive amounts of Levothyroxine won't damage your thyroid gland but excessive amounts can cause atrial fibrillation which can cause strokes. If you make sure your FT4 and FT3 remain within range you will not be over dosed.


hey Clutter u ok?tx for the reply

why too much levo wont damage thyroid gland, but taking too much iodine will destroy our thyroid?its a little bit confusing because from what ive read from this site levo contains iodine



I wasn't aware that taking too much iodine would destroy the thyroid gland. Too much iodine can induce autoimmune thyroiditis (Hashimoto's) and because Levothyroxine does contain atoms which convert to iodine patients don't usually need additional iodine supplementation.


clutter if you patience could you pls explain me why too much iodine can provoke hypothyroism, or worsen hypothyroidism to pple who already suffer from it, and why too much levo wont make hypothyroidism get worse in pplr who already have hypo, im confused



I suggest you Google "Iodine + Hashimoto's" and "Iodine + Hypothyroidism".

Iodine has been used to reduce T4 and T3 levels and raise TSH levels in hyperthyroid patients so it is not a suitable therapy for hypothyroid patients.

Over dosing Levothyroxine won't make hypothyroidism worse but it will cause over medication symptoms similar to being hyperthyroid.

I don't understand why you are asking about too much Levothyroxine. Too much Levothyroxine is not a good thing. You should take the minimum dose required to make you feel well and keep your FT3 level within range.

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I think you're confusing iodine with levo. Iodine is an ingredient of thyroid hormone. One molecule of T4 has four atoms of iodine, it's not all iodine.

So, in 100 mcg T4, you have 65 mcg T4, which isn't very much.

Taking large doses of iodine on top of that, will stimulate the thyroid gland. Stimulating a sick gland is not a good idea and will make it die off more quickly, that's all. And, we are talking about sick glands here, not healthy glands.


Hi Veganman,

In answer to your question, I was born with a partial thyroid that has never worked. Was on the same dose of 200 mcg until I was 32 with no problems. After that, my problems did start. (too long a story) Anyway I was told that quote (never forget the words) "Too much levothyroxine is bad for the heart, BUT if you are not getting enough, they (the professionals) will prescribe the higher dose anyway!!!!" The highest dose I have been on is 250 mcg of the levothyroxine and 20 mcg of the Lithyronine. The lowest was 75 mcg (I was dropped from 200 to 75 mcg at the start of my problems)

I did find the 250 mcg was too much for me, I did not feel well on it at all and found it hard to sleep. I am back on my original dose of 200 mcg which is best for me, although it is taking its time to adapt, I feel that I am back to being me. I am also taking 20 mcg of the lithyronine. My last results indicate, I am at the right level.

What dose are you on? You say that your partial gland works, so what is your TSH level? The reason I ask is, that if you have too much levothyroxine, it will suppress your natural levels of hormones, hence being overdosed. The idea is that if you have a thyroid working, the medication is there as a top up to get back to normal levels. Everyone is different. In my case, the medication does all the work for me as my partial thyroid has never worked. There is a big difference.

Hope that makes sense and take care :)


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