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Thyroid UK
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Help with t3 + t4 dosages

I am just about to start taking t3 a well as t4, but don't really trust my doctor who does not seem very well informed about thyroid issues.

I am taking 50 mcg levothyroxine. Should I start the t3 at 25mcg as instructed, or a lower dose to begin with - say 10mcg? And should I lower the t4? If so - by how much?

What is a 'normal' dose?

I do not want to change my doctor as at least he is willing to prescribe t3.


6 Replies

Your dose of levo is very small, so I am sure you will benefit from the T3. I am not medically qualified. but this is an extract.

Liothyronine is four times more potent than levothyroxine. Levothyroxine 100 mcg daily would be equal to 25 mcg of liothyronine. This is approximately equivalent to one grain of the desiccated thyroid medications.

To add liothyronine to levothyroxine, the dose of levothyroxine may need to be lowered first. Someone taking levothyroxine 100 mcg daily might be changed to levothyroxine 75 mcg with liothyronine 5 mcg daily. This would be roughly the same as 95 mcg of levothyroxine, not exactly the same dose but a close approximation.


As you are on 50mcg I would halve the T3. If you should feel overstimulated just reduce it the following day and increase gradually over the next few weeks.

I was on 75 mcg levo and reduced to 50 and took half T3. I found taking T3 very calming after taking levo only.

I hope all goes well. Levo is the inactive hormone and T3 the active. The purpose of T3 is that it enters your cells very quickly but the benefits of the action on the cells lasts between 1 and 3 days.



Thank you very much indeed! This is really helpful and encouraging. Stay well....



There is no normal dose. It depends on pulse rate and body temperature. It also depends on how you feel. Your body produces both t4 and t3 , why not replace them both? Some people take 7 grains of dessicated thyroid while others take 1 grain. I feel way better on dessicated thyroid than I did on straight t4.

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Thank you for this - it is really helpful and encouraging. I am starting to hope I'll get my life back!

Stay well....


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I'm no expert, but +1 on the often published x 4 or 5 rule of thumb. That 1mcg of T3 is roughly equivalent to 4 or even 5 of T4.

As a rule of thumb it isn't always reliable. If as in my own experience a person is taking a given quantity of T4 (say 160mcg) and at that is close to being fully replaced but hasn't in fact been able to utilise all of it because of e.g. a conversion issue - then it's quite possible that taking the nominally equivalent 160/4 = 40 mcg of T3 could leave them over replaced. That is if it turns out that they are able to properly use all of the (more easily utilised) T3.

That sort of thing might happen because e.g. they were maybe only using 120mcg of the 160mcg dose of T4. Which if the x4 rule is applied might mean 30mcg of T3 would be a more correct equivalent for them. i.e. 40 mcg could easily leave them hyper/over replaced.

Especially since the excess of 10mcg of T3 is actually quite a large amount of hormone - equivalent by the same rule to 40 or even 50mcg of T4.

Another consideration as the others say is that not everybody does best on the same proportion of T3 to T4. The possibilities seem to range from feeling perfectly well on T4 only, to needing 100% T3 to feel well - with others needing a proportion somewhere in between to feel best.

There's in my experience quite a lot to be said for staying on as much T4 as works. It's for example more widely available, and is less sensitive to the timing of when it's taken during the day, avoids the need to break the daily dose into several lots taken through the day, results in minimal effects if you e.g. have supply problems and miss a day or two compared to T3 and and so on.

My story is different to many, but I for example started on only 10mcg daily of T3 with around 150mcg of T4, and while it wasn't enough for me (i was still prone to fatigue issues) it transformed my life compared to the full blown hypo symptoms I experienced while taking T4 only. It was stepped up to 20mcg of T3 with 125mcg of T4 after a few years, which was even better.

It's only very recently that I've started to experiment with even higher proportions of T3. Which have produced some further improvement, but in mostly mental and motivational terms. This at the price of a certain peakiness in energy as the T3 kicks in and fades out - i'm actually going to seek to try increasing my T4 dosage a bit more in the hope of a better compromise.

The other basic factor is how much hormone in total a person may need anyway. If for example they have a part functioning thyroid the dose required to give proper replacement may be quite low. If on the other hand they have e.g. no thyroid following a thyroidectomy then they will likely require a higher total dose of hormone. There's another commonly quoted rule of thumb that suggests a given dose in mcg of T4 per kg of body weight for example.

From what i've been able to glean it's factors like this (and there are more) that mean that most doctors and endos will seek to ramp both the total dose of hormone and the proportion of T3 fairly gradually. Most are especially cautious around T3, and it does need care - too much too quickly is capable of producing very unpleasant effects....




I was on t4 only, and was feeling terrible, fatigue and bloated, difficult to loose weight. Here in Brazil it's VERY difficult to find a doctor that gives t3 too, and here the dissected thyroid is not selled. So I went to another doctor and he gave me 15mcg T3, 3 times a day, 9 AM, 3 PM and 7 PM , with t4 100 mcg at the morning together with the T3. I feel much better, and I'm taking it two weeks ago. But I feel hypo at night and the morning, as a result of having less T3, so it means my T4 is not being converted to t3, or that it is rT3. I am also taking Selenium or Brazil Nuts, and Lugol (inorganic iodine).


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