MESO-Rx

Anabolic Steroids

The T3/T4 Trap: How Thyroid Hormones Destroy Your Hard-Earned Muscle

Type-IIx

Type-IIx

Member
image_square_no_preview.webp

Author​

Cormac Mannion (Type-IIx)

Date​

Friday, October 03 2025

Introduction​

Key Takeaways​

Key Takeaways

  1. Exogenous T3 significantly breaks down muscle protein
  2. T3 selectively destroys growth-responsive type IIA muscle fibers
  3. GH naturally increases peripheral conversion of T4 to T3, which is beneficial
  4. The reduction in serum T4 from GH use is typically not problematic for healthy individuals
  5. Thyroid hormone supplementation is irrational for bodybuilders as it accelerates muscle loss
  6. Exogenous GH cannot cause central hypothyroidism but may reveal pre-existing conditions
  7. Thyroid hormone misuse carries serious health risks including cardiac arrhythmias
  8. Common bodybuilding practices of using T3 deep into competition prep can be extremely destructive to muscle mass
Share

Introduction​

Here’s another Q&A format article that was asked by a user in the Team Ampouletude Telegram group and led to a fruitful discussion… and fleeting references to still widespread bad practices among bodybuilders with respect to thyroid hormone use… something so destructive to muscle mass deep into prep when it’s typically applied… commonly with a hand-wave to the effect that “he’s on Halo, he won’t notice any muscle loss…“

Thyroid hormone is potently muscle catabolic. It chews through muscle aggressively and selectively, especially the growth-responsive type II fibers.

Question​

Since exogenous growth hormone (exogenous GH) reduces serum T4, should a healthy bodybuilder supplement exogenous T4 (Levothyroxine; Synthroid; Tiromel) or T3 (Liothyronine; Cytomel) as a rule with exogenous GH?
Click to expand...

Definitions​

T3: Triiodothyronine

T3 (exogenous) [Cytomel, LT3]: Liothyronine

T4: Thyroxine

T4 (exogenous) [Tiromel, Synthroid, LT4]: Levothyroxine

T3 in its endogenous (triiodothyronine) and exogenous (liothyronine) form is the actively catabolic hormone among the thyroid hormones (e.g., T2, T3, T4). T4, despite some endogenous effects, for enhanced bodybuilding discussion is effectively the prodrug to the active T3.

fT3; FT3: free T3, the bioactive fraction in blood

RMR: resting metabolic rate

REE: resting energy expenditure

UCP: uncoupling protein

LBM: lean body mass

Dose-Response​

Metabolic Rate​

Given a seventy-five microgram (75 µg) Cytomel dose (daily for 14 days):

  • fT3 increased by 1.7-fold
  • RMR increased by 15% (adjusted for LBM)
  • UCP2 increased 1.7-fold and UCP3 increased 2.4-fold. [1]
A trend was also seen for a direct correlation between REE/LBM and increases in fT3 levels, with an average 0.11 kcal/kg/d increase in REE/LBM for each 10 pg/dL increase in fT3.
Click to expand...

Read More on Substack​

Substack | Read​

 
Sort by date Sort by votes
aaronben said:
Personally when I was 20, about 30 years ago with 3-400mcg max of T4 a day and few steroids on me, I was ripped, I never tired, I was always hungry and at night I could eat even 4 large bowls of ice cream with related croissants
Click to expand...
300-400mcg of T4 is in the toxic range....are you sure you were taking that much? And for how long? Also no sides ,like high heart rate, anxiety etc?
 
Upvote 0 Downvote
Any thoughts on how Sobetirome GC-1 might fit into this and if it would lead to a differrent outcome that T3 use?

I am also supplementing T4 while running GH, currently 100mcg pre-bed with 8IU hgh. On an 8am blood draw my T3 and T4 come back in range. Without it my T4 seemed to keep lowering on blood tests, and I assumed that would eventually lead to lowering T3.

Is this a misconception? I'm very keen to know.
 
Upvote 0 Downvote
JPMOTM said:
Any thoughts on how Sobetirome GC-1 might fit into this and if it would lead to a differrent outcome that T3 use?

I am also supplementing T4 while running GH, currently 100mcg pre-bed with 8IU hgh. On an 8am blood draw my T3 and T4 come back in range. Without it my T4 seemed to keep lowering on blood tests, and I assumed that would eventually lead to lowering T3.

Is this a misconception? I'm very keen to know.
Click to expand...
Yes, it's a misconception. It's normal for GH to "pull" on T4 to increase T3 – it's abnormal for T4 to go out of range. If it goes out of range substantially, then it just means you already had central hypothyroidism
 
Upvote 0 Downvote
Type-IIx said:
Yes, it's a misconception. It's normal for GH to "pull" on T4 to increase T3 – it's abnormal for T4 to go out of range. If it goes out of range substantially, then it just means you already had central hypothyroidism
Click to expand...
Ok great, I'll drop the T4 and do bloods in a month and see how I look. The less I have to take the better.

8IU GH, 500mg L-Carnitine and 100mcg T4 turns me into a furnace overnight! I also think the T4 might be responsible for elevating my RHR. During prep it was about 61. Since adding reta, GH, T4, reducing cardio and gaining 16kg in 4 months its up to 80! I've added in some more cardio now but hopefully this help too.
 
Upvote 0 Downvote
This is interesting, I'm on armor thyroid now, but I used to be on t3 20 mcg a day. One time I did very fast prime/cut and was at 60mcg a day, lost 40 lbs in a month and was the leanest I've ever been before I started my cycle, I may have gone up to 100 during that time but can't remember. I had all my muscle back in a matter of weeks if not more muscle and then of course a successful cycle with further muscle gain. I've dieted harshly other times and didn't get near as good of results as this. Muscle retention was a lot better and I lost more bodyfat using the t3.
 
Upvote 0 Downvote
Who cares (outside of bodybuilders who I consider as pussies) about losing 5-10 percent of your muscle mass as long as your gettin down to sub 10 percent bf . T3 is magic to keep up your metabolism while losing fat even when your sub 10 percent.
 
Upvote 0 Downvote

Type-IIx said:
View attachment 352276

Author​

Cormac Mannion (Type-IIx)

Date​

Friday, October 03 2025

Introduction​

Key Takeaways​

Key Takeaways

  1. Exogenous T3 significantly breaks down muscle protein
  2. T3 selectively destroys growth-responsive type IIA muscle fibers
  3. GH naturally increases peripheral conversion of T4 to T3, which is beneficial
  4. The reduction in serum T4 from GH use is typically not problematic for healthy individuals
  5. Thyroid hormone supplementation is irrational for bodybuilders as it accelerates muscle loss
  6. Exogenous GH cannot cause central hypothyroidism but may reveal pre-existing conditions
  7. Thyroid hormone misuse carries serious health risks including cardiac arrhythmias
  8. Common bodybuilding practices of using T3 deep into competition prep can be extremely destructive to muscle mass
Share

Introduction​

Here’s another Q&A format article that was asked by a user in the Team Ampouletude Telegram group and led to a fruitful discussion… and fleeting references to still widespread bad practices among bodybuilders with respect to thyroid hormone use… something so destructive to muscle mass deep into prep when it’s typically applied… commonly with a hand-wave to the effect that “he’s on Halo, he won’t notice any muscle loss…“

Thyroid hormone is potently muscle catabolic. It chews through muscle aggressively and selectively, especially the growth-responsive type II fibers.

Question​


Definitions​

T3: Triiodothyronine

T3 (exogenous) [Cytomel, LT3]: Liothyronine

T4: Thyroxine

T4 (exogenous) [Tiromel, Synthroid, LT4]: Levothyroxine

T3 in its endogenous (triiodothyronine) and exogenous (liothyronine) form is the actively catabolic hormone among the thyroid hormones (e.g., T2, T3, T4). T4, despite some endogenous effects, for enhanced bodybuilding discussion is effectively the prodrug to the active T3.

fT3; FT3: free T3, the bioactive fraction in blood

RMR: resting metabolic rate

REE: resting energy expenditure

UCP: uncoupling protein

LBM: lean body mass

Dose-Response​

Metabolic Rate​

Given a seventy-five microgram (75 µg) Cytomel dose (daily for 14 days):

  • fT3 increased by 1.7-fold
  • RMR increased by 15% (adjusted for LBM)
  • UCP2 increased 1.7-fold and UCP3 increased 2.4-fold. [1]


Read More on Substack​

Substack | Read​

Click to expand...
@Type-IIx what is your opinion about GC-1 Sobetirome and the claim of it having similar fatloss effects as T3 while not beeing (nearly as) catabolic?
 
Upvote 0 Downvote
I've used t3 in eighty percent of competition preps. After trial and error , I use it 5-6 weeks out. 50 mcg is highest I've gone this prep and last few. Some people's t3 is normal range on 50 mcg


Can you get peeled inside out with low t3 levels? Yes

It's basically insurance

I've gone 75 mcg which is highest I would go but 50 mcg to be safe. I've gone 100 mcg for a short while before. 37.5 if you're really scared or on the super safe side. 25 mcg is a replacement dose usually

Again lab results are key to see how t3 works

T3 generally come back swiftly.. after 5-6 weeks mine are in normal range . Some say 2-3 weeks

My sister and I took 5-6 weeks to get labs done after stopping thyroid drugs. She was in t4 and hers came back fine, as did mine, after 6 weeks, which I think the doctor recommended that time frame to test
 
Upvote 0 Downvote
Im on 150mcg t4 and 20mcg of t3, because i was hypothyroid, that combination puts me within the range, but i feel very flat, even when i eat 4000 calories, (im not hyperthyroid). and weight stalls, should i increase the calories? im trying to gain weight atm
 
Upvote 0 Downvote
AnabolicTacos said:
Im on 150mcg t4 and 20mcg of t3, because i was hypothyroid, that combination puts me within the range, but i feel very flat, even when i eat 4000 calories, (im not hyperthyroid). and weight stalls, should i increase the calories? im trying to gain weight atm
Click to expand...
Remove the t3/t4 and that should fix it. Too much thyroid will make you flat and catabolize your muscle.
What's your TSH first thing in the morning before taking your thyroid meds?
 
Upvote 0 Downvote
AnabolicTacos said:
i tried going without them, but im always hypothyroid, as i said its just a "replacement" dose
Click to expand...
I gotcha. I was just trying to find out if it's replacement to like a 3 tsh, which is still normal range" or to what's more considered "trt optimized" TSH of 1 or less. That could just be a little too much and maybe you need to split the dose in half or divide up the t3. That's all. I tried the to do the thyroid optimization with my trt doc to understand what is all about. My natural TSH was a 3 which is still in range but on the middle to higher side. He got me down to around 1.2 TSH but I just didn't like it. I was hungry all the time. It was harder to stick to a diet. I felt hotter in the sun than normal, etc.
In the end it just worked more against my progress than to help it
 
Upvote 0 Downvote
You must log in or register to reply here.

Similar threads

Type-IIx
How Exogenous GH Blunts GH Secretagogues' Effects – And How to Deal with It
Replies
8
Views
1K
MrTexas2
M
godt240
complete info guide on HGH
2
Replies
30
Views
10K
serkan
S
colossus25
Why you should be running T4 with your GH
2 3 4
Replies
77
Views
8K
Jeffg353
Jeffg353
C
  • Question Question
Fat loss notes
Replies
12
Views
3K
IndividualMan
I
bigrobbie
Acronyms, abbreviations, etc...for the newbie to discussion forums!
Replies
5
Views
1K
mchef168
mchef168

Sponsors

Latest posts

Back
Top