Human Growth Hormone (HGH)
HGH · Somatropin · GH
Recombinant growth hormone; supports lipolysis, recovery, IGF-1 elevation.
Key takeaways
- Recombinant growth hormone approved for GH deficiency; identical to the pituitary 191-amino-acid peptide.
- Short ~4-hour serum half-life, but the IGF-1 effect persists — daily dosing sustains the signal.
- 1 mg ≈ 3 IU; the dataset range 0.5–4 mg spans replacement through supraphysiological community dosing.
- Fluid retention, carpal tunnel symptoms, and insulin resistance are the documented dose-dependent risks.
Overview
What it is
Somatropin is recombinant human growth hormone, identical to the 191-amino-acid pituitary peptide. It's approved for growth hormone deficiency in children and adults and used off-label for recovery, fat loss, and anti-aging. Effects run through direct receptor action and hepatic IGF-1 production.
Pharmacokinetics
Subcutaneous somatropin has a short serum half-life of roughly 4 hours, peaks around 5 hours post-injection, and shows about 63% bioavailability. Downstream IGF-1 elevation persists far longer than the GH pulse itself, so once-daily dosing sustains the effect. One milligram is roughly 3 IU.
What the evidence says
For genuine deficiency, replacement is backed by decades of randomized trials showing body-composition and quality-of-life benefits. Supraphysiological use in healthy people rests on thinner ground: fluid retention, carpal tunnel symptoms, and insulin resistance are well documented, and the long-term safety of sustained IGF-1 elevation is unresolved.
Reported dosing protocols
Protocols reported in research literature and clinic/community use — informational context, not a dosing recommendation.
| Use case | Dose | Route | Frequency | Duration |
|---|---|---|---|---|
| Adult GH deficiency (label) | 0.15–0.3 mg (~0.5–1 IU) start | SubQ | Once daily | Chronic |
| Recovery / body composition (community) | 1–4 IU (~0.3–1.3 mg) | SubQ | Once daily | ≥12 weeks |
Pharmacokinetic summary
- Model tier
- Advanced (t½ + Cmax + Tmax + F)
- Half-life
- 4.1 hours
- Cmax
- 622.9 ng/mL
- Tmax
- 0.2 days
- Bioavailability
- 63%
- Typical dose
- 0.5–4 mg
Frequently asked questions
Why is the half-life so short but dosing only daily?
The ~4-hour half-life describes circulating GH, but the biological effect runs through IGF-1, which stays elevated for many hours after each pulse. The serum GH level at any moment is a poor proxy for total daily effect.
Does growth hormone build muscle in healthy adults?
Trials in healthy adults show increased lean body mass, but much of it is water and connective tissue rather than contractile protein, and strength gains are inconsistent. It reduces fat mass more reliably than it builds functional muscle.
What are the real risks of long-term use?
Documented dose-dependent effects include fluid retention, carpal tunnel syndrome, joint pain, and insulin resistance. Whether sustained IGF-1 elevation raises cancer risk is unresolved; acromegalic features appear only at extreme, prolonged exposure.
References
- Nature / PMC HGH PK — 1 mg ≈ 3 IU.
- PK profile of IV and SC recombinant hGH (Pediatric Research 1988) — Source of the dataset half-life and bioavailability values.
Related compounds
MK-677 (Ibutamoren)
Orally active growth hormone secretagogue (ghrelin receptor agonist) that elevates GH and IGF-1; the non-peptide counterpart to injectable GHRPs.
MGF (Mechano Growth Factor)
IGF-1 splice variant produced in response to mechanical load; involved in muscle repair signaling.
PEG-MGF (Pegylated MGF)
Pegylated mechano growth factor with extended half-life versus native MGF; used for recovery research.
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