# T3 (Triiodothyronine)

Category: Hormones

Also known as: T3, triiodothyronine, liothyronine

T3 (triiodothyronine) is the metabolically active derivative of thyroxine, the hormone that directly promotes respiration and energy production in virtually all tissues. Peat identified T3 as the basic anti-stress hormone, a co-factor for cellular energy production whose…

12 passages · 2 authors · 1993–2022 · Most-cited: [Ray Peat](https://bioenergeticoracle.com/md/voices/ray-peat/index.md)

Canonical page: https://bioenergeticoracle.com/concepts/t3-triiodothyronine

## Synthesis

**T3 (triiodothyronine)** is the *metabolically active derivative of thyroxine*, the hormone that directly promotes respiration and energy production in virtually all tissues. [Source 3] Peat identified T3 as the **basic anti-stress hormone**, a co-factor for cellular energy production whose presence reinforces the organism's structure and function. [Source 4] While the thyroid gland secretes a small portion of active T3, approximately 70% is produced in the liver through the enzymatic conversion of thyroxine (T4), a process that depends critically on the availability of glucose and allows metabolism to be sensitively adjusted to nutritional status. [Source 3, 7, 12]

The distinction between T3 and its pro-hormone T4 is central to Peat's critique of modern thyroid therapy. Peat argued that T4 alone, when administered to women or stressed individuals, often fails to restore metabolism because it can suppress the pituitary's thyroid-stimulating hormone and shut off the gland's own T3 output without being adequately converted to the active hormone in the liver. [Source 7] He cited experiments showing that T4 added to brain, heart, and muscle tissue *suppressed oxidative metabolism*, while T3 universally increased respiration. [Source 3, 7] This conversion block is frequently driven by estrogen, which interferes with liver function and shifts metabolism toward fatty acid oxidation, wasting oxygen and preventing T4-to-T3 conversion. [Source 10] Consequently, Peat observed that women are about five to ten times more likely to have thyroid problems than men, and that a physiological mixture of T3 and T4—imitating the gland's natural secretion ratio—is the most practical therapeutic approach. [Source 7, 8]

The biological activity of T3 is not reliably indicated by standard lab measurements. Peat stressed that **free T3** is a laboratory concept, and that T3 bound to its transport proteins, particularly transthyretin, can demonstrably enter cells, mitochondria, and nuclei. [Source 5] Because T3's actions can be inhibited by polyunsaturated fatty acids, reverse T3, and excess thyroxine, the absolute serum level of T3 cannot be used alone for diagnosis. [Source 5] Reverse T3 partly occupies the same response sites as active T3, competing against it, and can accumulate when local clearing enzymes are blocked by stress substances. [Source 11] Peat instead recommended functional assessments: T3 promotes rapid cholesterol utilization, so serum cholesterol rises in hypothyroidism; it prevents unnecessary lactic acid production, making blood lactate a useful marker; and it regulates serum sodium, magnesium, calcium, and glucose. [Source 5] He also noted that a person's temperature and pulse rate before and after T3 administration reveal whether it is affecting metabolic rate. [Source 1]

Therapeutic T3 use requires attention to dosage, ratio, and route. Peat noted that a typical effective oral dose is 5 mcg of T3 with each meal, and that the half-life of T3 is only about 12 hours to a day, compared to T4's two-week half-life, meaning TSH changes can occur within hours of T3 supplementation. [Source 6, 8] The optimal ratio of T3 to T4 varies by individual; those under estrogenic or stress-induced conversion blocks often do better on higher T3 ratios such as 1:2 or 1:1, and Georgi Dinkov has reported preferring a ratio closer to **3:1** by supplementing additional T3. [Source 10] Topically applied T3 can be very beneficial for rashes and other skin problems, with local concentration remaining high if the solution penetrates about half a centimeter before dilution by blood, though Peat doubted enough would be absorbed to correct general hypothyroidism. [Source 1, 9] T3 is also the precursor for **pregnenolone**, produced from active thyroid hormone, cholesterol, and vitamin A in the mitochondria, positioning T3 as foundational to all downstream steroid hormone synthesis. [Source 2]

## People also ask

### How does T3 differ from T4 in its effects on metabolism?

Peat argued that T3 universally increases respiration and energy production, while T4 can suppress oxidative metabolism in tissues like brain, heart, and muscle, especially when conversion to T3 is blocked.

### Why might women need a higher T3 to T4 ratio in thyroid therapy?

Peat observed that estrogen often interferes with liver function and blocks T4-to-T3 conversion, making women more prone to thyroid issues and often benefiting from a physiological mixture with a higher T3 ratio.

### What functional signs did Peat recommend for assessing T3 activity instead of blood tests?

Peat recommended tracking cholesterol levels, blood lactate, serum minerals, and body temperature and pulse rate before and after T3 administration, as these reflect its metabolic effects more reliably than serum T3 measurements.

## Related concepts

- [Thyroid](https://bioenergeticoracle.com/md/concepts/thyroid/index.md)
- [Adrenaline](https://bioenergeticoracle.com/md/concepts/adrenaline/index.md)
- [Arthritis](https://bioenergeticoracle.com/md/concepts/arthritis/index.md)
- [Cortisol](https://bioenergeticoracle.com/md/concepts/cortisol/index.md)
- [Dental Health](https://bioenergeticoracle.com/md/concepts/dental-health/index.md)
- [Endotoxin (Lipopolysaccharide, LPS)](https://bioenergeticoracle.com/md/concepts/endotoxin-lipopolysaccharide-lps/index.md)

## Cited passages

Passage numbers match the `[Source N]` markers in the synthesis above.

### Source 1 — Ray Peat Email Advice Depository — Post 322

Ray Peat · Email · Dec 18, 2016

> **Question:** Dear Dr. Peat, Coffee consistently causes diarrhoea, insomnia, anxiety and jitteriness, while caffeine dissolved in vodka or ethanol applied in even large amounts topically doesn't even interfere with sleep, and actually improves alertness within half a minute of application. Orally consumed thyroid also gives me very similar symptoms and curiously seems to increase oestrogenic symptoms like bloat and emotional lability. In your most recent KMUD interview, you spoke about how the gut finds it relatively difficult to process pure chemicals, and thus I was wondering if you think topically applied T3 could be beneficial? If so, would ethanol be a viable solvent? Also, can you provide some references showing that good thyroid function leads to a sterile gut?
>
> **Ray Peat:** On the skin it can be very beneficial for rashes and other skin problems, but I doubt that enough would be absorbed to correct a general hypothyroidism. If you check your temperature and pulse rate before and after, you can tell whether it’s affecting your metabolic rate.

### Source 2 — Becoming Stress Proof

Danny Roddy · Article · http://www.thepeatwhisperer.com/email0

> - Triiodothyronine (T3) - Two of the most prominent thyroid hormones in the body are thyroxine (T4) and the more metabolically active triiodothyronine (T3). T3 is made from an enzymatic conversion from T4 predominantly in the liver.
>
> - Youthful Protective Hormones - Pregnenolone, progesterone, thyroid (triiodothyronine, or T3), testosterone, and dehydroepiandrosterone (DHEA)

### Source 3 — Thyroid: Misconceptions

Ray Peat · Newsletter · Nov 1993

> It is the metabolically active derivative of thyroxine, somewhat as insulin is the activated form of proinsulin. When thyroxine is added to brain tissue in vitro, it suppresses respiration; but when triiodothyronine is added to any tissue, respiration is increased. Triiodothyronine (T3) is mostly produced in the liver, depending on the availability of glucose to the liver, allowing a sensitive adjustment of metabolism to nutrition.
>
> Armour thyroid, USP, is often said to be of imprecise dosage, but in fact every batch is biologically standardized, and studies have shown it to be reliably within 1 of the labeled potency. The best known brand of the supposedly chemically precise levothyroxine, however, was for a long time 30 below the labeled potency.
>
> If the liver is the main source of the thyroid problem, then thyroxine pills can make the problem worse, by suppressing the portion of T3 still coming from the thyroid gland. Armour thyroid, USP, Thyrolar, Euthroid, Proloid, and a few other products contain both thyroxine and T3, in approximately the proportion secreted by a normally functioning gland.
>
> Unsaturated oils interfere with thyroid function in several ways, including blocking the digestive proteolytic enzymes involved in the release of hormone from the globulin. Unsaturated fatty acids interfere with binding of the hormone to a transport protein, and with the conversion of T4 to T3 in the liver and in the pituitary. Linoleic and linolenic acids are roughly twice as toxic to these systems as oleic acid is. The tissue response to the hormone is inhibited by unsaturated fats in proportion to the number of double bonds in the fat. A deficiency of polyunsaturated fatty acids is anti-estrogenic, partly by allowing the thyroid-stimulated liver to excrete estrogen, and partly by failing to activate the pituitary secretion of gonadotrophins.
>
> G. W. Crile found that the basal metabolism of the people in Yucatan, where coconuts are a staple food, is 125 of that of people in the United States. Animal experiments show that coconut oil added to a normal diet can lower serum cholesterol levels. There is a very reliable inverse relationship between the level of serum cholesterol and thyroid hormone action.

### Source 4 — Danny Roddy - Why Sugar Is Healthy, Stress, Hormones & Reversing Baldness With Diet

Danny Roddy · Interview · Oct 29, 2012 · https://www.youtube.com/watch?v=2ELOooPT2As

> **Justin:** And you know what's cool about the work on the thyroid and the hormones is that, you know, someone may be listening to this and, you know, they've got a great head of hair and they're blessed in that way, which is great. But the, you know, having proper thyroid health affects, doesn't it, just about everything, which directly affects your hormones. But then after that, it's sort of the master switch for everything, isn't it?
>
> **Danny Roddy:** Yeah, I think it's, Peat calls it the basic anti-stress hormone. And a lot of the idea that the adrenals are, the adrenal glands are more important. Peat kind of, his work kind of summarizes suggest that that's not true, but I really do think the thyroid, active thyroid hormone triiodothyronine or T3 is the basic anti-stress hormone. I think physiologically it makes sense. It's a co-factor for your cells to produce energy. And then if you think about the organism's ability to produce energy being the most important important thing for reinforcing the structure in every part of you, it makes kind of more sense in that context. At least that was kind of what helped me wrap my head around it.

### Source 5 — Preventing and treating cancer with progesterone.

Ray Peat · Article · 2007 · https://raypeat.com/articles/articles/hypothyroidism.shtml

> Because the actions of T3 can be inhibited by many factors, including polyunsaturated fatty acids, reverse T3, and excess thyroxine, the absolute level of T3 can't be used by itself for diagnosis. "Free T3" or "free T4" is a laboratory concept, and the biological activity of T3 doesn't necessarily correspond to its "freedom" in the test. T3 bound to its transport proteins can be demonstrated to enter cells, mitochondria, and nuclei. Transthyretin, which carries both vitamin A and thyroid hormones, is sharply decreased by stress, and should probably be regularly measured as part of the thyroid examination.
>
> When T3 is metabolically active, lactic acid won't be produced unnecessarily, so the measurement of lactate in the blood is a useful test for interpreting thyroid function. Cholesterol is used rapidly under the influence of T3, and ever since the 1930s it has been clear that serum cholesterol rises in hypothyroidism, and is very useful diagnostically. Sodium, magnesium, calcium, potassium, creatinine, albumin, glucose, and other components of the serum are regulated by the thyroid hormones, and can be used along with the various functional tests for evaluating thyroid function.
>
> Stereotypes are important. When a very thin person with high blood pressure visits a doctor, hypothyroidism isn't likely to be considered; even high TSH and very low T4 and T3 are likely to be ignored, because of the stereotypes. (And if those tests were in the healthy range, the person would be at risk for the "hyperthyroid" diagnosis.) But remembering some of the common adaptive reactions to a thyroid deficiency, the catabolic effects of high cortisol and the circulatory disturbance caused by high adrenaline should lead to doing some of the appropriate tests, instead of treating the person's hypertension and "under nourished" condition.
>
> [references]

### Source 6 — Ray Peat Email Advice Depository — Post 207

Ray Peat · Email · Jan 14, 2016

> **Question:** Dear Ray, I am in the UK and wanted to obtain some T3 and T4 to start taking for type one diabetes. The Mexican Pharmacy are only selling a product called Triyotex now. I can't seem to find out if this is T3 or T4 or a combination. Would this be suitable and how would I split the tablets to begin. With Cynoplus you said 5/6 pieces built up over a few weeks plus some T4 to suppress TSH.
>
> **Ray Peat:** I think Triyotex is T3, 75 mcg, which would be three times as much as Cynomel, but I haven’t tried it, and don’t know how effective it is. Usually, a 5 mcg dose of T3 with each meal is effective. Anti-aging Systems in England has a large variety of thyroid products.

### Source 7 — Politics & Science: Thyroid and Regeneration

Ray Peat · Interview · Sep 11, 2008 · http://www.l-i-g-h-t.com/files/politics-science-thyroid-and-regeneration.mp4

> ## T3 vs. T4: The Active Hormone
>
> **Ray Peat:** In the 1950s, it was discovered that one molecule called T3, triiodothyronine, is the active promoter of respiration. But it took decades for that information to circulate through the American medical community. The Japanese, Israelis, and Russians were the first ones to really assimilate that information. Since estrogen inhibits the activity of the thyroid, women are about five or ten times as likely to have thyroid problems as men. But when one form of synthetic thyroid, T4, which isn't the active respiration promoter, was created chemically and became a product, it was tested on 25-year-old male medical students in good health. It was found to act just like the desiccated thyroid glands that had been used at that time for 50 years. The marketers began selling it to females without really testing it on females, because it worked on young men. But in fact, it very often interferes because the pituitary and brain will respond to it and shut off the thyroid stimulating hormone. It's good at turning off a woman's thyroid gland without necessarily being converted in the liver into the active form. An experimenter in the 1960s who hadn't assimilated the knowledge of the two hormones—which normally exist in a ratio of three or four to one—sliced up pieces of muscle, kidney, liver, heart, and brain, and then added what he called the thyroid hormone thyroxine, or T4, to the solution. He found that it suppressed oxidative metabolism in the heart, muscle, and brain. The liver was the only gland that was strongly responsive to increasing its respiration rate in proportion to the amount of added thyroxine. He said he had demonstrated that respiration isn't the important thing done by the thyroid hormone, because how could it be important if the thyroid hormone suppresses the metabolism of the brain and the heart? But in fact, the liver is the source of about 70% of the active thyroid hormone that circulates in the bloodstream.

### Source 8 — One Radio Network: Ray Peat with Patrick Timpone — September 21, 2021

Ray Peat · Interview · Sep 21, 2021

> **Patrick Timpone:** But they work the same well, if I understand correctly. They work just as well?
>
> **Ray Peat:** They have both... Active components, T3 and T4.
>
> **Patrick Timpone:** So the ones that are going around now, they're T3 and T4?
>
> **Ray Peat:** They're a mixture? That's the most practical physiological mixture. It imitates the natural glandular balance.
>
> **Patrick Timpone:** And the natural glandular balance, what does that have in it? All of them as well?
>
> **Ray Peat:** Yeah, it also has a little bit of of the precursors, T1 and T2. T2 works just the same as T3, practically, but there's only a very tiny amount of that.
>
> **Patrick Timpone:** Dr. Ray Peat Patrick Timpone tomorrow we're going to talk with Charlie Sewell Charlie's got a very concise we think well thought out he has a whole team of one page religious exemption for this jab we're going to talk about it tomorrow we'll go through it line by line it's just one page Not guaranteeing it's going to work, but if someone is forcing you to do something, you might want to get this. We'll send it to you, and you make two copies, send one, and we'll tell you how to do it. That'll be tomorrow at 10 o'clock. Charlie's a very smart guy. He's got some Supreme Court things in there, and pretty interesting. And then Dr. Thomas Cowan and Andrew Kaufman are going to be here tomorrow at 1 o'clock, and we'll talk more about their work tomorrow. Dr. Peat, while I've got you here, I know that you've liked their work, Kauffman and Cowan, but you've disagreed with a few things. What's the number one thing you kind of disagree with their show-me-the-virus theory?

### Source 9 — Ray Peat Email Advice Depository — Post 388

Ray Peat · Email · Jun 21, 2017

> **Question:** So if T3 is converted into T2 by healthy mitochondria then topical T3 does not sound like it would have negative effects besides the possibility of taking too much at once . Would the threshold be quite lower than for an oral dose since the effects are regional?
>
> **Ray Peat:** If it penetrates about half a centimeter into the skin before it’s greatly diluted by the blood, the local concentration could be high with moderate absorption. People have had good results using a solution with 10 mcg in 100 ml. on skin rashes.

### Source 10 — #80: World War 3  |  Heavy Metals  |  Progesterone for Hair Loss  |  T3 to T4 Thyroid Ratio with Ray Peat

Ray Peat · Interview · Mar 4, 2022 · https://www.youtube.com/watch?v=LDWVtsqEOF0

> ## Thyroid Health: T3 and T4 Ratios
>
> **Danny Roddy:** I've been noticing a theme where people are doing significantly better on a 1:2 or 1:1 ratio of T3 to T4, rather than the traditional 1:3 or 1:4. Why would someone do better on a higher ratio of T3?
>
> **Ray Peat:** If you are under the influence of something like estrogen, which interferes with liver function and oxygen use—causing a shift to fatty acid oxidation—this wasting of oxygen prevents the conversion of T4 to T3. The conversion requires a certain level of glucose. High-estrogen women frequently have a block between T4 and T3. In a healthy young man, T4 works almost exactly like T3. In women, it's about 10 times less likely to be adequate because estrogen is a deterrent to conversion. Similarly, men under stress who have done too much aerobic exercise can't get their T3 to come back because factors like aromatase have been activated. So, if you give a ratio that has enough T3 to keep the oxidative system running, and just enough T4 to fill in when there's a dip in energy availability, that helps. Everyone has their optimal ratio.

### Source 11 — Ask the Herb Doctor: Rheumatoid Arthritis

Ray Peat · Interview · Oct 21, 2016

> ## Thyroid Hormones: T3, T4, and Reverse T3
>
> **Caller:** Does T3 affect TSH?
>
> **Ray Peat:** Yes. Normally T4 suppresses TSH because the pituitary converts T4 to T3 locally. But if you get enough T3 into your brain and pituitary, it is at least as effective as T4.
>
> **Caller:** What about Reverse T3?
>
> **Ray Peat:** Reverse T3 partly occupies the same response site that active T3 would, simply competing against it. Local enzymes can eliminate Reverse T3, but if those are blocked by stress substances, Reverse T3 can accumulate.
>
> **Sarah Murray:** That's why taking temperatures and pulses will tell you if you're getting enough T3 or converting T4 properly.

### Source 12 — The Thermo Diet Podcast Episode 78 - Life, Liver Health, & More with Danny Roddy

Danny Roddy · Interview · Apr 25, 2021 · https://www.youtube.com/watch?v=eo4LvSaq_9Q

> **Danny Roddy:** Yeah, Ray has called it the chemist of the body. And I think one of the immediate things that I think of is there's like deiodinase enzymes that convert thyroxin into triiodothyronine or T3. And so I forget the exact percentage. You might know. It's like how much thyroxin is produced in the thyroid gland.

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