Thyroid UK
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Advice on starting T3 please

Hi, Today my Endocrinologist prescribed me some T3 to take alongside my T4. I have been taking 137.5mcg Levo and have been told to switch to 100mcg Levo plus 20mcg t3 to be split and take half in the morning and half in the evening. I am very excited to try the T3 as I have never really felt well on T4 only and first asked to try it 4 years ago. I am just wondering what to expect when I first start taking it. Will I notice a difference straight away? Am I likely to get side effects that will settle later? Do my Endo's recommendations seem reasonable? I'm excited to try it, but also a little nervous about the change. Any advice or insights would be very welcome. Thanks x

4 Replies

Hi Woochan, I'm 7 weeks into T3 in addition to T4. I was told to take the first 10mcg in morning but the second 10mcg dose before 4pm as "its notorious for keeping people awake" - whether that is true or not I don't know and suspect it depends, patient to patient. Within 48 hrs I noticed my fog brain had dramatically reduced and within 4 weeks the fatigue had also reduced but not to same level. Only side affects I have noticed is psoriasis I have is little worse and I have gained/bloated but I really suspect that is down to incorrect dosage that a "tweak" would sort out.

Good luck and hope it brings much needed relief!


Woochan, it won't hurt to take 10mcg for a few days to see how you tolerate it while the higher dose Levothyroxine washes out. You can take the first dose with your Levothyroxine and the second dose 8-16 hours later. I take my second dose at bedtime.

It takes 36-48 hours for T3 to reach the cells before it starts working. The lower your FT3 is the quicker you're likely to notice any benefit, but it still takes 4-6 weeks to metabolise. I found an improvement in brain fog and mental clarity within a week. You may notice slightly faster pulse and heart rate an hour to 90 minutes after ingestion but it will usually subside to normal within an hour. Skip the next dose if it doesn't. It only takes 6 hours for T3 to clear the blood so any discomfort will soon ease.

Adding T3 to T4 was very positive for me. I hope it works as well for you.

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Hello Woochan,

I recently added T3 to my T4 and the positive effect was almost immediate (within two days). I have lost all symptoms expert tinnitus and insomnia.

I would definately recommend as feel so much better.

I take mine 7am with T4 and then second dose at 3pm in afternoon.

My dose is 100/75 mcg alternate days Levo and 20mcg T3.

Good luck & post any more questions//anxieties.



Hi there

With the addition of T3, I too noticed a difference in the first week - less brain fog and tiredness. I have also managed to lose some weight.

When I first started on it I had a few hot sweats and palpitations but they settled down after a couple of weeks and were not as bad as I have felt previously when I increased my Levo.

I am now on 100mcg Levo and 30 mcg T3 of which I take 10mcg when I wake and 20mcg at 2pm. I am still not feeling perfect but am so much improved compared to when I was on Levo only.

Good luck :-)


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