The clinical literature spans replacement-dose protocols (100 mg/week — restoring low-end-normal serum testosterone in primary hypogonadism) to supraphysiological investigation arms (600 mg/week — measuring upper-end anabolic response in healthy controls). The landmark dose-response data come from two Bhasin studies that established the framework still used today.
TRT / hypogonadism restoration — the lower bound
Replacement protocols in the published endocrinology literature: 100–200 mg testosterone enanthate per 1–2 weeks. The Bhasin 1996 reference arm used 100 mg/week, producing serum total testosterone in the 500–800 ng/dL range — mid-reference for adult males. This is the dose that puts back what the body stopped making, without exceeding physiological signal.
Clinical TRT in current practice has shifted toward higher cadence (twice-weekly 50–80 mg dosing) and slightly higher weekly totals (140–200 mg/week) to maintain serum testosterone in the 700–1000 ng/dL range, which produces better symptomatic response than mid-reference.
Supraphysiological / hypertrophy research — the published dose-response curve
Bhasin 1996 included a 600 mg/week arm — six times replacement dose. The untrained group on testosterone alone gained ~6 kg lean mass over 10 weeks. The trained group on the same dose gained ~12 kg. Both far exceeded the placebo + training arm.
Bhasin 2001 directly measured the dose-response curve. Twenty-week protocols with healthy men randomised across 25, 50, 125, 300, and 600 mg/week:
- 25–50 mg/week: below endogenous replacement (these subjects had pituitary suppression to standardise); net catabolic, lean mass declined.
- 125 mg/week: maintained lean mass at baseline; the threshold dose for net anabolic effect.
- 300 mg/week: 5–6 kg lean mass gain over 20 weeks; modest hypertrophy with significant strength response.
- 600 mg/week: 7–8 kg lean mass gain over 20 weeks; the upper plateau in the studied range.
The dose-response between 125 and 600 mg/week is approximately linear for lean-mass change. Above 600 mg/week the curve flattens — the published data do not strongly support proportional benefit, while side-effect markers (E2, HCT, lipids) continue scaling roughly linearly. The research consensus is that 600 mg/week is the practical upper bound where benefit-to-side-effect ratio remains favourable; above that, side-effect cost outpaces marginal anabolic gain.
Mechanism — why dose response runs through free testosterone, not total
Exogenous testosterone elevates total serum testosterone proportionally with dose. The biologically active fraction — free testosterone, plus the weakly-albumin-bound “bioavailable” component — depends additionally on SHBG response. Higher testosterone exposure suppresses SHBG production over 4–8 weeks, which amplifies the free-fraction rise beyond what the total-testosterone curve alone predicts. Clinical effect tracks free testosterone, which is why subjective response often exceeds what weekly mg numbers would suggest.
HPTA suppression saturates rapidly: pituitary LH falls below detection within 14 days at any dose above replacement. The user gets full HPTA shutdown at 200 mg/week and full HPTA shutdown at 600 mg/week — the suppression cost is constant past the lower threshold.
Research-framed dosing — practical translation
- First cycle: 300–500 mg/week × 12 weeks. Below 300 mg the response is modest; above 500 mg on a first cycle the side-effect risk is unjustified for the marginal gain.
- Subsequent cycles: 400–600 mg/week × 12–16 weeks. The upper end approaches the supraphysiological response curve’s plateau.
- Cruise / TRT-range research: 150–200 mg/week indefinite. Maintains serum testosterone in optimal range with minimal side-effect drift.
- Recomposition (cutting + lean-mass preservation): 200–300 mg/week paired with caloric deficit and adequate protein. Sufficient anabolic signal to preserve lean mass during deficit; not so high that water retention masks composition change.
Frequency — pharmacokinetic justification for twice-weekly
Testosterone enanthate has a serum elimination half-life of 4.5–5 days. Once-weekly administration produces a peak-to-trough swing of approximately 2× — peak at 36–72 hours post-injection, trough at 7 days. Twice-weekly (Monday/Thursday at half the weekly dose each) cuts the swing roughly in half, producing a flatter serum curve.
Practical effects of twice-weekly dosing:
- Estradiol management is easier — aromatisation rate tracks substrate concentration, so a flatter testosterone curve produces a flatter E2 curve.
- Mood lability around the trough day disappears.
- HCT drift is marginally slower (mechanism unclear; consistent observation in the TRT clinical literature).
- SHBG response stabilises slightly faster.
The trade-off is logistical: twice the injection events per week. For users tolerating once-weekly without symptoms, twice-weekly is optional rather than required. For users with E2 management difficulties or pronounced peak-trough symptoms, twice-weekly resolves most of the variance.
The drift in “standard” community dosing
What forums describe as “standard” first-cycle dose drifted upward across decades — from the 1990s 250 mg/week baseline to the 2010s 500 mg/week assumption. The pharmacological case for the higher dose is weak: 250 mg/week already exceeds physiological replacement by 2.5×, produces measurable lean-mass gain, and carries lower side-effect cost than 500 mg/week. The 500 mg dose is not inherently incorrect — it sits within the published response curve — but the assumption that more is necessarily better at the first-cycle stage does not survive the dose-response data.
For a first cycle, the defensible range is 250–500 mg/week. Lower end produces less but cleaner; upper end produces more but at higher physiological cost. Both are within the research framework.