Thyroid UK
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When IS the right time to test when on T3 only?

Hello everyone - two questions in a row. Sorry but I'm really puzzled.

When is the right moment to test FT3 when on T3 only and multidosing?

I take:

20mcg as a T3 circadian method dose at 5:00.

10mcg at 10:00

10mcg at 13:00

10mcg at 16:00 sometimes more if very active afternoon

5mcg at 19:00

5mcg at lights out

I have been on this regime for four months, I felt better on 70 mcgs but have not been able to raise (debilitatingly low cortisol afternoons, just low mornings).

How and when do I test to see what is really going on?

I have a very good lab near me and can get any tests done at reasonable costs i e I could even test multiple times a day if that's what's needed.

As always any ideas and advice greatly welcome and appreciated.

PS All the usual suspects have been tested and are being supplemented, without great improvememts so far.

18 Replies


There's no restriction on the number of questions you may ask :)

Leave around 12 hours after last dose to avoid the T3 peaking in your serum.


I am not a medical professional and this information is not intended to be a substitute for medical guidance from your own doctor. Please check with your personal physician before applying any of these suggestions.


Thank you on both points!


I take my T3 once daily. I am well and have had not untoward experiences. Just for info this is a link from a doctor (now deceased) who took his dose of T3 (150mcg) in the middle of the night so that nothing interfered with the uptake.

If taking thyroid hormones our stomach has to be empty so that nothing interferes with the uptake. If food has been taken, a two hour wait at least before taking hormones and waiting about an hour afterwards is recommended.

Just for info: this is a link by Dr Lowe with explanation about T3 .

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shaws - how I would love to be able to do that, maybe one day! So far, whenever I try to consolidate into fewer doses the rollercoaster feelings become too strong. I felt good on a trial of hourly small amounts of T3, including a crumb every time I woke up at night --- not possible in the long run.

I have compounded sublingual T3 tablets - don't they bypass the 'empty stomach' rule?

Thank you for the link, it's open and waiting in another window!


I am not medically qualified but as far as I'm aware, your body indicates that the dose has passed optimal when you have unpleasant symptoms and the dose is then reduced slightly till you have none.

Excess normally gives the unpleasant symptoms. Although others might have different optinions.

I've no idea how sublingual T3 works, as far as I know the molecules in thyroid hormones are too large to pass through the tongue. In the USA for instance, it is forbidden by the FDA for thyroid hormones to be taken other than swallowed with water.

I have calculated that your 60mcg of T3 is equal, in effect, to around 230mcg levothyroxine and I do know some take higher doses.

From my own bad experience on levo and I also had severe palpitations on levothyroxoine (about 75mcg to 100mcg levo) but when switched to T3, haven't had one palpitation yet (very thankfully) and whole body calmed down.

Best wishes.

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This link might also be helpful. Dr L used T3 only for thyroid hormone resistant patients. Go to the date February 1, 1998 on the following link:

Extract from another part within December 24, 1997:-

And ". . . caused strokes"? If anything, the use of T3 may help prevent strokes. I scanned MEDLINE for studies on "T3" and "strokes" published between 1966 and 1997. These key words were mentioned in 43 publications. Most publications reported the beneficial effects of T3 on cardiovascular function. The word "stroke" was most often used in regard to the "stroke work in cardiac contractility" (a physiological description)—not in the sense of cerebrovascular accidents (strokes). I'll mention just a few representative publications. These suggest that it is urgent for the physician you mention—for his patients' welfare—to quickly update his knowledge.

In one study, a researcher found that T3 levels were significantly lower in 42 of 65 stroke patients. [Liang, D.S.: Stroke and thyroid hormones. Chinese Journal of Neurology & Psychiatry, 24(6):352-354, 384, Dec., 1991] It is certainly possible that the low levels of T3 were partly responsible for the strokes.


shaws - that is very interesting about the FDA's stance! I asked my compounding pharmacy... and they don't actually know about molecule size and if sublingual take up is possible or not.

Also thank you for pointing me towards hormone resistance, something I definitely need to look into more!


I take my L-T3 twice daily. I don't think we need to worry about absorbing T3 as it is a smaller molecule than T4 and more readily absorbed (95% v ~50%). In terms of when to take blood for an fT3 assay I'd suggest you try a simpler regime of twice daily medication. I found it is important to have sufficient T3 at night for good deep sleep. If you find you can't get to sleep you are probably taking too much. I would have the blood taken 4 to 12 hours after the last dose. In any event you are taking 70 mcg L-T3. Your fT3 will be around 10 - 15 and your TSH 0.01 or less. There! I've saved you the cost of a blood test !!! Seriously, what do you want the blood test for? It will show an above limit fT3 and a suppressed TSH.


Hi jimh111

when do you take your T3 & in what doses?At present I take 25mcgs at 5.30am,20mcgs @ 6pm approx & 10mcgs @ 12pm.I would like to take 2 doses a day as it easier to work around food,drink,supplements.

I tried taking 50mcgs in one go,but my heart pounded.I had supraventricular tachy & ectopic beats on thyroxine for 18 years.Down to virtually zero on T3.Just had 6 weeks trialling adding NDT,reducing T3.Result was a return of tachy & ectopic.Back on T3-only.


Varies between 40 and 50 mcg, equally split between 3 minutes before my breakfast porridge and just before bedtime. e.g. 20 mcg in the morning and 20 mcg at bedtime. If I have a blood test I have it in the morning before taking my L-T3 and then add 10% to the fT3 figure to get a 'real' average level estimate allowing for the short half-life.

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Thanks for the free blood test! Let's see if my doc accepts it...

Last week's was taken four hours after the last dose (10mcg) and was over range for FT3, I will go tomorrow and have it redone at ten hours without T3.

The reason I am keen on numbers is that my symptoms have changed dramatically, suddenly and if I am indeed over range for the first time ever I will then have to search for the reason.

I would like to dose less frequently and am happy for you that it works, but I have not been able to so far, there must be underlying reasons. I seem to run out after three/four hours, no matter how high or low the dose.

I will keep a close eye on the correct nighttime amount as well, there is a definite correlation to quality of sleep (waking up frequently, getting to sleep is never a problem)

Much food for thought, thank you for your input.


I found if my L-T3 dose is too high I don't get to sleep easily, if it is too low I fall asleep but it is light sleep and I keep waking up.

There's another post today about flame retardants and thyroid disorders. I suspect this is a common problem. One hypothesis I have is that as we overcome hypothyroidism our metabolism speeds up and we eliminate these toxins. Consequently we need a lower dose. If we go too low the toxins build up again and vice versa. So if you do feel overactive reduce your dose a little. Changing the dose little and often is better than waiting and doing a big change.


Oh that is interesting, jimg111 - and makes a lot of sense in connection with allergy and hypersensitivity symptoms which are reduced and manageable one day and then return with a vengeance out of the blue, together with a bunch of other nuisances.

Coincidentally I am having an environmental chemicals/MCS bloodtest done tomorrow which includes flame retardants ... I think your hypothesis has merit!


Can you give details of this test? Checking for PBDE flame retardants is very difficult and very expensive, so I wonder what your test is.


The description of the bloodtest talks about type 4 allergies, about anorganic, organic and chemical compounds, about cellular instead of IgE antibody testing methods. The method used is called LTT (lymphozyte transformation test).I will add the gandolinium from my recent mri to the substances tested for.

The flame retardants on the list are TCEP, TBEP, TEHP.

In Germany flame retardant materials are not mandatory for domestic use.

None of this really answers your questions, sorry!


Thanks. It doesn't assay flame retardants, just immune response.


Sorry, I could have worded that more accurately!


No problem at all. These toxicology assays are so specialist and expensive that I jump on any info that might be around.


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