Testosterone dose–response relationships in healthy young men
Bhasin et al. suppressed endogenous production and assigned healthy men to graded weekly testosterone doses. The controlled design helped isolate how circulating testosterone relates to lean mass, fat mass, strength and physical power.
Design
Controlled dose-response
Endogenous production suppressed
Doses
25–600 mg/week
Five graded weekly doses
Measured
Lean mass, strength, fat
Fat-free mass, leg strength and power
Result
Graded response
Gains rose across the dose range
Structured abstract
Method
Endogenous testosterone production was suppressed so that every participant started from the same place. Healthy men were then assigned to one of five graded weekly testosterone doses, so the resulting serum levels — and their effects — could be attributed to the dose rather than to individual differences.
Result
Fat-free mass increased progressively across the tested dose range. Leg strength and power rose with higher exposure, and fat mass decreased at the higher doses. The tissue effects did not plateau at the top of the ordinary physiological range.
Conclusion
Muscle and fat respond in proportion to how much hormone is actually circulating. The trials describe dose response; they do not define a universal treatment target and do not establish long-term safety at supraphysiological doses.
Why it matters
Fat-free mass and power rose across the graded weekly doses.
Study design
Same men, same conditions, only the dose changed
The design is tightly controlled because the starting point was set by the investigators rather than observed.
Step one
Suppression
The participants' own testosterone production was switched off, removing individual baseline differences from the comparison.
Step two
Five graded doses
Men were assigned to weekly doses from 25 mg to 600 mg, producing a wide and deliberately spaced range of serum levels.
Step three
Direct measurement
Fat-free mass, muscle size, leg strength and leg power were measured rather than inferred from how participants felt.
Body composition
Fat-free mass and fat mass
Function
Leg strength and leg power
Exposure
Serum testosterone per dose group
Duration
20 weeks of treatment
Five weekly doses, five different outcomes
The lowest doses did not simply do less — at the bottom of the range, men lost lean mass and gained body fat.
Fat-free mass
Progressive
Lean mass rose across the whole tested dose range, without plateauing inside the ordinary physiological range.
Leg strength and power
Rising
Strength and power increased with higher circulating testosterone.
Fat mass at higher doses
Falling
Fat mass decreased at the higher doses, completing the graded body-composition response.
The detailed per-dose figures used elsewhere on this site — including the mean on-treatment testosterone for each group — are shown in the dose-response graphic in the article library, drawn from the same publication.
Why the low-dose result matters most
The clinically interesting part of this experiment is not the top of the range but the bottom of it.
Low doses were not neutral in this trial
At the lowest doses, participants lost lean mass and gained body fat while still nominally being treated.
Lowest dose groups in the same trial
Tissue versus mood
Muscle and fat kept responding as exposure rose, whereas drive, mood and libido tend to level off within the ordinary range.
Interpretation across the wider literature
Why protocols differ
In this trial, body-composition response scaled with circulating level; it did not measure symptoms or long-term outcomes.
Practical reading of the dose-response curve
Clinical interpretation
Level, not label
In this trial, response tracked the level actually achieved rather than the fact of being treated, which may help explain why men on similar therapy respond differently.
It does not show which level is right for an individual man; that is a clinical judgement made with a physician.
None of this justifies supraphysiological dosing. The two highest arms are evidence about biology, not a protocol, and long-term safety at those levels was not established here.
Your own numbers
In this trial, response tracked the level reached.
Before any of this applies to you, the starting point has to be measured properly.
- Total testosterone and SHBG by LC-MS/MS
- Free testosterone calculated from both
- Haematocrit as a baseline safety marker
- A physician to set and review the target