Response to testosterone varies several-fold between people at the same exposure. Androgen receptor genetics (CAG repeat length) sets sensitivity and cannot be changed. Training age, calories and protein, sleep, and whether the product is what the label says can be changed and together explain more of the gap than genetics. Product quality alone is a coin flip: a third of black-market products are counterfeit and another third substandard.
- Shorter androgen receptor CAG repeats mean higher receptor activity; response to testosterone treatment was inversely related to CAG length in hypogonadal men (Zitzmann and Nieschlag).
- Even in Bhasin's controlled trials, individual fat-free mass changes at the same dose spanned a wide range around the group mean.
- Training roughly doubled the gain at a given dose in the 1996 trial; untrained or under-trained users leave half the effect on the table.
- A systematic review of 5,413 black-market samples found 36% counterfeit and a further 37% substandard: the labelled amount is often not the delivered amount.
- Sleep restriction lowers testosterone, impairs recovery and shifts weight loss toward muscle; it is the most under-rated variable in results.
The spread is real
In Bhasin’s trials, men on the same dose for the same weeks gained very different amounts. The group mean is what gets quoted; the individual values scatter widely around it. Five factors account for most of the scatter.
1. Receptor genetics
The androgen receptor gene contains a repeated CAG sequence. Fewer repeats, more active receptor. Zitzmann’s work in hypogonadal men found that the response to testosterone treatment, in body composition and other androgen-dependent traits, was inversely related to CAG length: same hormone, larger effect in men with shorter repeats. You cannot change it. You can stop comparing yourself to someone who drew a different number.
2. Training age and stimulus
Testosterone amplifies the training signal. In the 1996 trial, training roughly doubled the gain at a given dose. A novice with a big remaining growth window plus the drug outgrows an advanced lifter near his ceiling on the same amount, and someone training badly on the drug can be outgained by someone training well without it. How to train while on.
3. Food
The hormone raises the rate at which muscle protein can be built; the protein and energy still come from the plate. In a surplus with enough protein, the higher ceiling is reached. At maintenance, gains are modest. In a deficit, testosterone preserves muscle and improves the ratio of fat to muscle lost, but it does not add tissue. Bulking numbers, cutting numbers.
4. Sleep
Short sleep lowers your own testosterone, blunts recovery, raises cortisol, degrades training quality and shifts weight change toward muscle loss. Androgens can worsen sleep in some people, especially via sleep apnoea in heavier lifters. Seven-plus hours is part of the dose.
5. The product
A systematic review of 5,413 black-market samples: 36% counterfeit, 37% substandard. The labelled amount is often not the delivered amount, and sometimes the compound is not the one on the label. Two people “on the same thing” may be on different things. The check is a trough testosterone at steady state and, for anything beyond testosterone, a lab test of the product. How to spot and verify.
Smaller factors
- Estrogen management. Too high blunts through water and mood; too low blunts directly, because estradiol contributes to the anabolic response and to joint tolerance of heavy loads.
- Body fat. More fat, more aromatase, more estrogen per milligram; leaner people get a cleaner response.
- Age. Older lifters respond somewhat less in absolute muscle and more in side effects.
- Consistency. Missed injections and erratic timing create swings that cost results and cause side effects.
What to do with this
Fix the changeable ones in order of size: training, food, sleep, product. Then measure: trough testosterone, hematocrit, lipids, waist, gym numbers. If the numbers say the hormone is there and the results are not, the answer is in the gym or the kitchen, not the vial.
Frequently asked questions
Why does my friend get more from the same amount?
Receptor sensitivity (genetic), a different training age, more food, better sleep, or a product that actually contains what yours claims. Usually two or three of those at once.
Can I test my androgen receptor sensitivity?
CAG repeat length can be sequenced by a genetics lab, but it explains only part of the variance and there is nothing you can do about it. Bloodwork and your own response are more useful.
Is it the product?
Often. With roughly a third of black-market products counterfeit and a third under- or over-dosed, an unexpectedly weak or strong response is a reason to suspect the vial before the body. Trough testosterone on a blood test at steady state is the check.
How much do calories matter?
Enormously. Testosterone raises the ceiling on muscle synthesis; the materials still come from food. In a deficit it preserves muscle; it does not build it out of nothing.
Does training age matter on steroids?
Yes. Novices gain fast with or without, and the drug amplifies whatever stimulus exists. Advanced lifters gain less in absolute terms from both training and the drug, because they are closer to their ceiling.
Sources
- Zitzmann M, Nieschlag E. Androgen receptor gene CAG repeat length and body mass index modulate the safety of long-term intramuscular testosterone undecanoate therapy in hypogonadal men. JCEM, 2007.
- Zitzmann M. Pharmacogenetics of testosterone replacement therapy. Pharmacogenomics, 2009.
- Bhasin S et al. Testosterone dose-response relationships in healthy young men. 2001.
- Fake anabolic androgenic steroids on the black market: a systematic review and meta-analysis. 2022.
- Bhasin S et al. The effects of supraphysiologic doses of testosterone on muscle size and strength in normal men. NEJM, 1996.