Log in
Thyroid UK
91,924 members106,190 posts

Argument for *not* reducing T4 when adding T3

Found the paragraph below on the site even more belower :)

A further complication of the use of T3 is due to the suppressive effect that it can have on TSH. The level of TSH influences the conversion of T4 to T3. A high TSH results in the maximum level of conversion of T4 to T3. A fully suppressed TSH will result in the conversion rate of T4 to T3 being reduced to the minimum level. For the patient on a combined therapy with T4 and T3 then this is very significant indeed. Some doctors attempt to perform simple mathematical calculations when they add T3 to their patient's T4. They reduce their patient's T4 dosage when T3 is added. Often there is no understanding that the added T3 is likely to have a suppressive effect on TSH and this is likely to downgrade any T4 to T3 conversion rate. Taking some of the patients T4 away as well is only likely to make things worse. So, finding the right balance of T4 and T3 can be an extremely challenging task.


Thoughts? It would appear to be a persuasive argument.



14 Replies

This is an excerpt and is self explanatory:-

Turkish researchers studied 226 obese or overweight female patients with in-range TSH and thyroid hormone levels.[4] The researchers found that obese females had higher TSH levels than lean females. The investigators also found a statistically significant positive correlation between TSH levels and body weight, waist size, and fasting insulin levels. They concluded, “This study strongly supports existing, but contradictory, evidence that TSH levels are positively correlated with the degree of obesity and some of its metabolic consequences in overweight people with normal thyroid function.” (Italics mine.)

The three studies I mention above were published in 2005,[3] 2007,[4] and 2008.[2] They were published in the long-gone wake of a 2000 report from the journal Thyroid.[5] In that study, which has largely been ignored by the endocrinology specialty, researchers compared the treatment of hypothyroid patients to that of thyroid cancer patients. They found that hypothyroid patients on T4 replacement doses (dosages of thyroxine that keep the TSH within range) gained weight. In contrast, thyroid cancer patients didn’t take replacement doses of T4; instead, they took doses of T4 high enough to suppress their TSH levels. And they didn’t gain weight. The researchers concluded that T4 replacement was in fact the cause of the hypothyroid patients’ weight gain: “The excessive weight gain in patients becoming hypothyroid after destructive therapy for Graves’ disease suggests that restoration of serum TSH to the reference range by T4 alone may constitute inadequate hormone replacement.”


1 like

That's interesting and might explain a few things!

But should a patient's dose of T4 be *reduced* when starting combination T4/T3 therapy? Conventional wisdom (and advice usually given here) says yes. But the Paul Robinson article would appear to debunk that, and for compelling physiological reasons.


That's the view of most Endocrinologists, whose main concern is the whereabouts of the TSH and it is usual to reduce T4 usually by 50mcg when adding 10mcg of T3 i.e. 10mcg is equal in effect to approx 40mcg so they usually reduce T4 by 50mcg.

This is another good article in which it says some of us need to have supressive doses to be well.


Personally, I don't think it necessary but whichever hormone T4 or T3 we have to be aware of pulse/temp etc. and reduce slightly if pulse is too fast. Hypo usually have slow pulse rate until optimum meds.


I Don't really understand his reasoning for not reducing the T4. He says that the lower the TSH, the lower the conversion rate. But, when you add T3, the TSH is going to go low. Continuing on the same dose of T4 is going to push the TSH even lower, surely, so having that extra T4 is not going to increase T3, it's just going to mean you have a lot of unconverted T4 sloshing around in the blood.

Have I missed something?


I don't understand either. They reduced mine when T3 was added (only 10mcg) but they wanted to withdraw T3 when next bloods showed very low TSH. I said no I wouldn't stop T3, so they reduced T4 even further. It was sufficient for me to know T3 was the way to go.


Hose, if someone is optimally dosed on T4, adding T3 without reducing T4 will overmedicate them.

If T4 dose isn't optimal then it shouldn't be reduced when T3 is added.

The initial T4/T3 dose prescribed may be a bit of a guesstimate but follow up blood tests should indicate whether the initial dosing was right or needs tweaking.


That's the logical explanation, but doesn't alwasy work that way. And doesn't fit in with Paul's explanation.


Have you seen this? It graphically depicts exactly what you're talking about! tiredthyroid.com/blog/2014/...

I agree, a patient's T4 should not be reduced when T3 is added, for another reason--T4 has it's own properties. Healthy pigs and humans secrete both T4 and T3. T3 adds a synergy. I don't understand why docs don't understand this basic concept!


That's another theory. But what about people, like Shaw's and myself, who can't tolerate T4. And the more the T4 is reduced, the better they feel, until they end up on T3 only, and - whoppee - they get their health back. T4, both synthetic and in NDT, made me very, very ill, and it's taken years to get back to where I was before I was diagnosed and put on Levo. Doctors Don't understand that concept, either!


I wish there were more studies on our different biochemistries, because that would be the only explanation for the differences. But what doctors are preaching, T4-only, simply doesn't even reflect normal thyroid physiology!


GG, I was unable to tolerate T4 only but am okay on T4+T3. I know T3 calms the adverse effects T4 causes and Shaws found the same before she went on T3 only. I don't understand why, though.


On T4+T3, I was better than on T4 alone, but I wouldn't have called it good! All things are relative! But on NDT I was so ill! And put on so much weight! I wouldn't dare try T4 again in any form.


GG, I stopped all the meds I was taking apart from T4 to see if interactions were causing problems. No improvement. Checked the excipients which were in most of the meds I was previously taking and some were common so I don't think fillers were an isssue. T3 has some of the same fillers as Levothyroxine but I was fine on T3 only. Definitely something about Levothyroxine only.


Well, yes, we know that, it's been said over and over again. T4 only doesn't work - or it may work for a little while, but will suddenly stop working. But the fact remains, some of us can't take T4 at all.


You may also like...