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Thyroid UK
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T3 and potential side effects

I'm on T3-only and wondered if there is a good link anywhere as to the side effects. My T3 is from Greece and the enclosed leaflet is all in Greek.

Yesterday I suffered from severe anxiety and I can say with absolute certainty that it was down to the T3. Aside from this - I have only experienced benefits.

Thank you

22 Replies


Have you checked your FT3 level? High FT3 can cause anxiety.

Possible side effects of T3 are on page 3 of the PDF in medicines.org.uk/emc/PIL.24...


It's not been checked in a while. I meant to before I started on Monday, but didn't. I'll do one.

There won't be any danger of being over range any time soon as on NDT 2.5 grains wasn't enough - TSH still 5.



If TSH was 5 on 2.5 grains NDT it's unlikely your FT3 is high. It's not worth testing FT3 until you have been taking 25mcg T3 for six weeks.


How much T3 are you taking ? Switching from T4 to NDT and then T3 in quite a short space of time must have been quite challenging for your body.

How are your levels of B12 - Ferritin - Folate - VitD ? Sometimes when these are low in range the thyroid hormones are not well metabolised. Also can produce symptoms you have mentioned 😊


I'm only taking 25mcg a day split into 2 doses. I started taking on Monday this week.

I take all the recommended vitamins; although really struggle with fitting the all in since starting T3.

Yes - Levo made me have a depressive episode of two weeks so I wanted off that. It did actually cut my TSH rapidly but FT3 was only just scraping into range.

NDT was much better for me, but didn't reduce my TSHand FT3 was still poor. That's why I'm on the T3-only now.

I know I have switched too quickly - was only diagnosed in October.


Oh dear ! do hope things soon improve for you. Thyroid balancing does take time it seems - I have been taking T3 for over 3 years and my FT3 remained stubbornly in the middle of the range. It could be absorption issues in my case - could it be yours ?

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The beautiful thing about T3 is that it's fast acting and quick to get out of your system

Acute anxiety is adrenal or psychological, not T3.

I had side effects with T3, itching, 20 minutes after Taking the tablet, sensitive to the fillers.

How much did you take? If you sent yourself way hyper you could get palpitations which may bring on anxiety.

Lots of people split their T3 dose to give themselves a more even effect over the day.

If you took a 20mcg tablet and it was your first one, that would have bee. Unwise. 5mcg to start with then build up.


I take 25mcg a day split into two doses.

I was less anxious yesterday. Hmmm maybe it is adrenal. When on Levo/NDT I had my hormones tested and they fell in range (I checked the print out) but they were done on one random day - not like I asked for.

I had morning cortisol blood test as part of a series of tests. The Endo said it was a good level and said my pituitary gland wasn't suffering as a result of the thyroid gland's failings. But I've never done a saliva cortisol test. Should I take one of these, do you think?

Apart from that my only thyroid symptoms are still a bit of fatigue, psoriasis is inflamed at the moment and weight - pretty much stagnant. But the anxiety - that was terrible.


I would try splitting even more, tiny bits every hour. I really don't think anxiety is a side effect.

We all get it now and then and Adrenal issues, whether bad enough to cause your physician to do anything or not can certainly screw with your ability to cope with loud noises new situations etc.

You could try licorice root for a short time, it's not recommended long term but it can support you through a rough patch.

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I had side effects which included hypertension and unless you have your own bp monitor you won't know if the anxiety you are having is also causing hypertension. I would get one if you don't have one already. I had to stop taking it.

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Me too, blood pressure just kept climbing and I had to stop t3 when it got waaay to high


I don't take t3, so can't comment on that, what I do know is if your psoriasis is inflamed then something is not right. It's one of my markers too. Maybe you need to 'start again'get the blood tests & then begin on the slow process of building up the t3.

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Oh yes - I definitely agree with you. My skin lets me know when things are not so good!


Helena, I've been using apple cider vinegar (the fermented one) and found my skin to have improved; softer and less dry. I also take enzymes but the vinegar helps the gut in many ways as well as keeps glucose under control.

Just take a teaspoon or two diluted in the same amount of water and drink just before eating lunch and dinner. It can improve the balance of flora which is at the base of the problems.


I find UniPharma T3 to be weak, compared to the NDT I take. I need two grains of WP Thyroid to three 25mcg UniPharma to feel ok. I now take a a combination of the two.

I experienced idiopathic anxiety attacks before I took THs, which I've read is an adrenal issue caused by low THs.

Try monitoring your temperature & heart rate. My blood tests are always in "normal range" with secondary hypothyroidism, so I go by how I feel.


Leverette, a doctor used to recommend magnesium for women who were having palpitations with success. I also discovered your adrenals need massive amounts when under stress. That may be the underlying adrenal issue.


Thanks, Heloise!

I've been taking magnesium for about 15 years. It wasn't palpitations I suffered with, & I couldn't describe it as anxiety attack. The unexplained incidences were sheer fright, which stopped once I reached an effective dose of NDT. I've never experienced anything like it since.

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This has happened to me as well. I would lower the dose just a bit. Then watch you labs.


Helena877 Side effects listed for Mercury Pharma T3, from their Patient Information Leaflet:

medicines.org.uk/emc/medici... (you need to download the pdf)

• Vomiting

• Insomnia

• Fever

• Intolerance to heat

• Tremor

• Temporary loss of hair in children

• Allergic rreactions such as rash, itching, oedema

• Angina pain

• Irregular, thumping or fast heart beats

• Muscle cramps or weakness

• Diarrhoea

• Restlessness or excitability

• Headache, face and neck redness, sweating

• Loss of weight



I am sorry you are feeling poorly. I notice you are on 2.5 grains of NDT & adding 20mcg T3 split in two doses. You may have made the switch a bit soon, as 2.5 grains isn't a big dose. T3 is a bit tricky to dose & usually a last resort.

I found t3 quite hard to tolerate initially as my adrenals were weak.

It may be worth considering having an adrenal saliva test & dropping t3 back to 5 at each dose. I'm t3 only now and it's also helpful to record your pulse, BP and temp during course of day.


This is an excerpt which you will find helpful and rest your mind about T3:

The physician should call a pharmacy and request the leaflet given to patients when they pick up a Cytomel (T3) prescription. The physician would learn, as the patient leaflet on Cytomel explains, "POSSIBLE SIDE EFFECTS: NO COMMON SIDE EFFECTS HAVE BEEN REPORTED with proper use of this medication." Other than Nystatin, he probably will find that no other drug he might prescribe is as free from adverse effects as T3.


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Helena....I was very interested in your post regarding caution when taking T3

I have been on T3 for 15 months and on the whole have felt very much better. However I have had periods of my Heart rate dropping to the 40s and later recovering back to the 80s. This has happened these last 3 weeks when I have been visiting a hot country, and I'm struggling with a very low heart rate and high BP. With no sign of returning to normal, which I am extremely worried about.

I was interested in the note about myxodaema as I have had it now for 3 years and it has never improved. What does it mean when the guidelines suggest caution when taking T3 if you have the condition myxodeama?

I was advised to begin T3 by a Dr as I was becoming toxic with T4. He knew I had Myxodaema so should I have been taking it at all, and could this be the reason of the rise in BP and low HR? Does anyone have an answer please?


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