Understanding the Bodybuilder’s Relationship with T3
Any bodybuilder engaged in high-intensity training has likely felt the connection between training intensity and T3 in their own body.
However, not many know the exact mechanism by which these two are connected and operate.
Even top-tier bodyplayers preparing for a stage often stop at the level of, “Ah, I guess I need to add some T3.”
Why?
Because the anatomical and biochemical explanation for that ‘why’ has always been a void. So, this information, shared only among bodybuilders in this field, is not some simplistic, single-celled-level talk like “using growth hormone raises T3.”
This is a briefing that digs deep into what mechanism causes such a change, why T4 alone is insufficient, and how mismanagement of this can lead to a thyroid bottleneck phenomenon, going all the way into the depths.
Especially when growth hormone is combined with anabolic steroids and insulin, the game becomes far more complex.
Going back in time to 1988
It might seem primitive now, but even back then, administering growth hormone to healthy adults resulted in decreased T4 (thyroxine), increased T3 (triiodothyronine), and suppressed TSH (thyroid-stimulating hormone).
The funny thing is that reverse T3, rT3 (the reverse-converted inactive form of T3), remained almost unchanged.
Simply put, GH drastically promotes the conversion from T4 to T3, and underlying this is a mechanism of stimulated peripheral deiodination.
This is not just a simple metabolic change; it’s a systemic feedback suppression that messes with the entire thyroid axis.
Simply put, GH drastically promotes the conversion from T4 to T3, and underlying this is a mechanism of stimulated peripheral deiodination.
This is not just a simple metabolic change; it’s a systemic feedback suppression that messes with the entire thyroid axis.
But research on children with growth hormone deficiency (GHD) is more complicated.
Some studies showed that GH administration actually suppressed thyroid function, slowing the rate of epiphyseal closure, while others found that thyroid levels returned to normal between 6 months and 2 years after treatment, allowing patients to stop thyroid medication.
What does this mean?
It means that GH therapy doesn’t necessarily destroy the thyroid itself, but rather acts as a whistleblower, bringing pre-existing, struggling thyroid function to the surface.
If you don’t understand this properly, bodybuilders can end up ruining their conditioning at the end of the season, wondering, “Why is my body so puffy?”
“Why is my metabolism so damn slow?”
A large-scale study on adult GHD patients paints a clearer picture.
Serum T4 decreased, rT3 (the reverse-converted inactive form of T3) increased.
But T3 and TSH showed little change.
The crucial point here is that 47% of the study subjects, who originally had normal thyroid function, were diagnosed with hypothyroidism after starting GH therapy.
Almost half of them had underlying thyroid problems exposed by GH.
The fact that they were originally GH-deficient adults introduces the concept of baseline thyroid axis sensitivity.
It means that when the body is already in a compromised state and GH hits it, the regulatory system can’t handle it and the balance is disrupted.
This isn’t just a simple side effect; it’s a strong warning that thyroid testing and functional support are mandatory if you’re going to use GH.
Subsequent large-scale studies say the same thing.
GH doesn’t just tweak thyroid numbers; it worsens pre-existing hypothyroidism, and this worsening is powerful enough to erode the very positive effects sought from GH therapy (fatigue recovery, increased muscle density, mental stability, etc.).
This is important because it means we need a protocol-based approach: it’s not just about looking at thyroid numbers as a numbers game; to properly extract the benefits of GH therapy, thyroid replacement therapy (administration of T4 or T3) must absolutely accompany it.
Interestingly, many experts view GH not as directly destroying or suppressing the thyroid, but as acting as a selective stimulant that exposes problems in an already poorly functioning thyroid axis.
However, looking at numerous data and phenomena observed in the actual field, it’s hard to fully agree with this opinion.
Chewing through dozens of papers and data from hundreds of top-level bodybuilders, GH clearly applies a direct physiological drive to thyroid hormones.
Specifically, T4 decrease, T3 increase, TSH suppression.
This isn’t just a minor side effect; it’s a powerful endocrine disruption and intervention induced by GH.
So, what is the core mechanism of this change?
First, GH drastically promotes the conversion process from T4 to T3, i.e., it increases the activity of peripheral deiodinase enzymes (D1/D2).
Second, GH suppresses TSH secretion.
The key player here is somatostatin.
Administering GH indirectly increases somatostatin secretion, and this somatostatin suppresses the hypothalamic-pituitary-thyroid axis, inhibiting TSH synthesis.
That is: GH administration → Increased Somatostatin → Decreased TSH
This kind of feedback loop is formed.
Third, whether all this action is due to GH itself or its proxy, IGF-1, is still debated.
There is no clear conclusion on how independently IGF-1 affects the thyroid axis.
So, how does all this complex information apply in the real world for a top-level bodybuilder aiming to conquer the stage?
That’s the core, isn’t it?
Using growth hormone decreases T4, increases T3, and suppresses TSH.
Looking at it simply, oh, that seems good.
You might think, but if this structure persists for months, the entire thyroid feedback system can go haywire.
If you don’t know this and just shoot GH recklessly, a hypothyroid state can hit you at the end of the season, causing your conditioning to crash completely, your mental state to deteriorate, your metabolism to halt, and your body to swell up—a total disaster.
Therefore, T4 or T3 supplementation must be included as an essential component of the GH cycle, and especially the technique of fine-tuning—when, how much, and how to administer T3—is damn important.
The design of the GH + T3 compound cycle, passed down to professional bodybuilders in the field, comes from this background.
For example, starting with 4IU of GH per day, then introducing 12.5mcg of T3 from week 2 and maintaining it for 6 weeks.
But this is just the starting point; reactions vary tremendously depending on individual body weight, gender, innate thyroid function, and even the type or dose of GH used.
That’s why blood tests, especially Free T3, Free T4, TSH, and rT3, are not an option but a survival strategy, requiring periodic checks to fine-tune the dosage.
Subsequently, check T3 levels via blood test and either increase to 25mcg or maintain the current dose.
A strategy of intermittently mixing in T4 (e.g., 50mcg every other day) is also utilized.
Going a step further, most experts rarely use GH alone.
They use it in complex combinations with anabolic steroids, insulin, and others, and the impact of this combination on the thyroid axis becomes much more complicated.
What about anabolic steroids?
They tend to lower Thyroid Binding Globulin (TBG) levels.
If TBG decreases?
An environment is created where free T3 and free T4 concentrations in the blood can temporarily increase.
Of course, if estrogen levels are excessively high, TBG might increase instead.
This can synergize with GH’s T3 conversion promotion effect, but it also acts as a variable that makes thyroid function even more unpredictable.
Ultimately, you can’t know without looking at blood data.
What about insulin?
This one doesn’t directly perform the magic of converting T4 to T3.
But it drives cellular energy metabolism and nutrient utilization efficiency to the extreme.
Especially when used with GH, these two amplify each other’s anabolic effects while driving the metabolic rate insanely high, and if the thyroid can’t keep up with this pace, the entire system grinds and creaks.
Using insulin incorrectly during the extreme calorie restriction at the end of a diet can actually inhibit the conversion of T4 to T3, accelerating a metabolic shutdown.
This means a situation can arise where the body is getting bigger and the metabolic rate is increasing, but the thyroid is exhausted and gives out.
Ultimately, thyroid management in a stack combining GH, anabolic steroids, and insulin requires a much more sophisticated radar network and feedback loop than with GH alone.
Let’s break it down simply.
GH drastically increases the speed of converting inactive T4 to active T3, while things like anabolic steroids can shake up the actual amount of thyroid hormone (free T3/T4) acting in the blood.
On top of this, insulin completely flips the entire playing field—the metabolic rate itself—of how cells use energy and absorb nutrients.
With these three factors pressuring the thyroid and its environment individually or simultaneously, the thyroid can’t get its act together, and eventually, the entire metabolic system can become a mess.
If you can’t conduct this symphony properly, you might end up not shining on stage, but being carried out to the emergency room.
Such compound cycles are much more favorable for body composition changes, fatigue management during the cycle, and maintaining and recovering metabolic rate at the end of the season compared to running GH alone, but risk management must be equally intense.
As a reference, it’s a famous incident in this field that Dallas McCarver, who once used massive amounts of GH, died young from thyroid cancer.
And it’s an open secret that other top athletes who have used excessive GH have faced similar problems.
Is this just a simple coincidence?
Highly unlikely.
There is a hypothesis that when GH suppresses TSH and abnormally stimulates or alters the thyroid, nodules or malignant cells can grow even without TSH stimulation.
Therefore, when designing a GH cycle, thyroid support therapy is not an option but a mandatory condition for survival.
In conclusion, growth hormone is not just a drug that burns some fat and makes you look younger.
It is a central endocrine regulator that directly manipulates the thyroid axis and is a decisive variable that determines the outcome of conditioning at the end of the season.
The success or failure of the entire cycle depends on when, where, and how you position each T3 pill, each T4 pill.
Especially if used with anabolic steroids and insulin, you must accurately understand the interaction each substance has on the thyroid and metabolic rate.
This is impossible without blood tests, and this is where experts and amateurs are separated.
Considering the complex interactions of growth hormone and other chemicals, this isn’t just a simple T3 patch-up prescription; it’s a high-level engineering domain that requires precisely understanding the role of each hormone, maximizing synergy, and minimizing potential conflicts.
So, don’t just thoughtlessly shove T3 in because you’re using growth hormone; first, properly understand the criteria for when, why, how much, and how to use it, and then dive in.
That is the decisive difference between an expert and an amateur.
References
1. “The Effect of Growth Hormone on Thyroid Function in Growth Hormone-Deficient Adults: A 5-Year Follow-Up Study”
Clinical Endocrinology (Oxf). 1999 Nov;51(5):549-55.
This study is a follow-up observational paper on what changes occur in thyroid function when GH is administered long-term to GH-deficient adults.
It shows that GH therapy can decrease serum T4 levels and, in some patients, unmask previously undiagnosed hypothyroidism or worsen pre-existing hypothyroidism.
https://pubmed.ncbi.nlm.nih.gov/10594515/
2. “Effects of Growth Hormone on Thyroid Function and on T4, T3, rT3 and TSH Concentrations”
British Medical Journal. 1980 Mar 29;280(6218):895-8.
This paper investigates the effects of GH on thyroid hormones T4, T3, reverse T3 (rT3), and TSH concentrations.
It presents results showing that after GH administration, T4 concentration decreases, T3 concentration increases, and peripheral conversion from T4 to T3 increases.
It also suggests that the TSH response may be blunted. This is one of the classic studies that can serve as the basis for the parts in the text stating “GH drastically promotes the conversion from T4 to T3, and underlying this is a mechanism of stimulated peripheral deiodination” and “TSH (thyroid-stimulating hormone) is suppressed.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1601299/
