Sixty-one trained men had their own testosterone shut off and received 25, 50, 125, 300 or 600 mg of enanthate weekly for 20 weeks. Fat-free mass, strength and fat loss rose with dose in a near-linear line; the two lowest doses left men below their own natural baseline. Hemoglobin and hematocrit rose at the higher doses and HDL fell at the highest. The curve has no plateau in the studied range, and neither does the side-effect curve.
- Design: 61 healthy, weight-trained men, 18–35, own production suppressed with a GnRH agonist, randomised to 25, 50, 125, 300 or 600 mg testosterone enanthate weekly for 20 weeks, no supervised training.
- Fat-free mass changed in a dose-dependent line: losses at 25 and 50 mg (below natural production), gains at 125, larger at 300, largest at 600, about +8 kg at the top.
- Leg-press strength and thigh muscle volume followed the same line; fat mass fell at the higher doses.
- Hemoglobin and hematocrit increased at 300 and 600 mg; HDL cholesterol fell at 600 mg; no plateau in benefits or in these effects within the range.
- The 125 mg group roughly matched natural production; everything above it was supraphysiological.
The study
Bhasin and colleagues, 2001. Sixty-one healthy men aged 18–35 with lifting experience. Their own testosterone was switched off with a GnRH agonist so that the injected amount was the only testosterone they had. Five groups: 25, 50, 125, 300 or 600 mg of testosterone enanthate weekly, for 20 weeks, followed by a 16-week recovery. Training was not supervised or changed. It remains the only controlled dose-response study of this kind and it will not be repeated.
What moved, by dose
| Weekly dose | Where it sits | Fat-free mass | Strength, muscle size | Fat mass | Hemoglobin / hematocrit | HDL |
|---|---|---|---|---|---|---|
| 25 mg | well below natural | fell | fell | rose | unchanged | unchanged |
| 50 mg | below natural | fell slightly | flat to down | rose | unchanged | unchanged |
| 125 mg | about natural | small gain | small gain | flat | unchanged | unchanged |
| 300 mg | supraphysiological | clear gain | clear gain | fell | rose | small change |
| 600 mg | supraphysiological | largest, about +8 kg | largest | fell most | rose most | fell |
The lines are close to straight. Each step up bought more muscle, more strength and more fat loss, and from 300 mg up also bought more red cells, and at 600 mg less HDL. Nothing plateaued inside the range.
Three things the curve tells you
1. Results are proportional. There is no threshold below which nothing happens and above which everything happens. Twice the hormone, roughly twice the gain over 20 weeks, in this range.
2. The side-effect line runs alongside. Hematocrit and HDL moved at exactly the doses that moved muscle most. In the ester article’s terms, the 300 and 600 mg groups were also the groups with the biggest weekly peaks; flatter dosing is one way to keep the benefit line and bend the side-effect line.
3. Below your own production you lose. The 25 and 50 mg groups were hypogonadal and lost muscle. That is what the recovery window after stopping looks like, and why keeping gains is about training and food through that window.
What the study does not tell you
- Training effect. No supervised programme. The 1996 trial by the same group showed training roughly doubles the gain at a given dose. Everything above is a floor, not a ceiling.
- Above 600 mg. Untested and untestable. Observational cohorts of heavier users show the hematocrit, lipid and cardiac lines continue; the muscle line is unknown.
- Other compounds. This is testosterone only. Other steroids have different anabolic-to-androgenic ratios, aromatisation and liver profiles; none has this quality of dose data.
- Duration. Twenty weeks. Results and side effects both continue to accrue with time on, which is why continuous use behaves differently from defined periods.
Using the curve
Pick the point on the line you want, knowing the other axis moves with it, and measure the other axis: blood pressure at home, hematocrit and lipids every two to three months. The study gives you the shape of the trade-off; your bloodwork tells you where you actually landed.
Frequently asked questions
What is the takeaway from the dose-response study?
More hormone, more muscle and strength, in a straight line across the tested range, and more hematocrit and HDL change along the same line. There is no free zone where results rise and side effects do not.
Why did the low doses lose muscle?
Because the men's own production was switched off. At 25 and 50 mg weekly they had less testosterone than before the study, so they lost fat-free mass. This is the same state as the recovery window after stopping.
Did the men train?
They were experienced lifters but training was not supervised or increased. The 1996 trial by the same group showed training roughly doubles the gain at a given dose.
Does the line keep going above 600 mg?
Nobody has tested it in a controlled trial and nobody will. Observational data on heavier users show the side-effect line continues; whether the muscle line does is unknown, and other compounds complicate the picture.
How does this translate to real use?
It tells you what a given amount of testosterone does over 20 weeks in a controlled setting: results are proportional, hematocrit and HDL move with them, and time on matters as much as amount. Where you sit on that line is a choice with a known trade-off on each axis.
Sources
- Bhasin S et al. Testosterone dose-response relationships in healthy young men. American Journal of Physiology, Endocrinology and Metabolism, 2001.
- Bhasin S et al. The effects of supraphysiologic doses of testosterone on muscle size and strength in normal men. NEJM, 1996.
- Pope HG et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. 2014.