Growth hormone: the GH axis
How the body controls growth hormone, and every drug and peptide that acts on it, with sources.
Checked 2026-10-22 Researched and written by Kymata Health Editorial · Sources cited inline Report an error
Short answer
The hypothalamus sends GHRH to switch growth hormone release on and somatostatin to switch it off; ghrelin from the stomach adds a second push. The pituitary releases GH in pulses, largest in early sleep, and GH makes the liver release IGF-1, which feeds back to slow it. Drugs act at each step.
How does the body control growth hormone?
The axis, step by step
- HypothalamusGHRH switches GH release on; somatostatin switches it off. (Mayo 1992, Mol Endocrinol; Dimaraki 2003, Am J Physiol)
- Stomach and hypothalamusGhrelin acts on its own receptor (GHS-R1a) and adds to GHRH, partly by overriding somatostatin. (Howard 1996, Science; Popovic 1995, JCEM)
- PituitaryReleases GH in pulses, about 14 a day when fed, largest at the first deep sleep (about 70% of daily GH in men). (Hartman 1992, JCEM; Van Cauter 1998, Sleep)
- Liver and tissuesGH raises IGF-1, which carries much of its effect. In adolescent boys, a GH pulse blunted the next GHRH response, more so with higher IGF-1. (Richmond 2002, JCEM)
The growth hormone family
GH itself, the drugs that make the pituitary release more of it, and IGF-1 downstream. Half-lives are human values.
Three ways to raise GH
| Class | Acts on |
|---|---|
| GHRH analog | GHRH receptor on the pituitary (cAMP) |
| Ghrelin-receptor agonist | Ghrelin receptor (GHS-R1a) in hypothalamus and pituitary |
| Growth hormone (daily) | GH receptor directly; bypasses the pituitary |
| Growth hormone (weekly) | GH receptor directly, released over a week |
| IGF-1 | IGF-1 receptor, downstream of GH |
Compared
16 agents| Agent | Class | Labelled product | Half-life (human) | Taken |
|---|---|---|---|---|
| Somatropin (rhGH) | Growth hormone (daily) | Genotropin, Humatrope, Norditropin, Omnitrope, Zomacton, Serostim | 2 to 3.8 h (SC, across labels) (Humatrope label) | Daily injection (label) |
| Somapacitan | Growth hormone (weekly) | Sogroya | about 2 to 3 days (adults) (Sogroya label) | Weekly injection (label) |
| Somatrogon | Growth hormone (weekly) | Ngenla | 37.7 h (effective, children) (Ngenla label) | Weekly injection (label) |
| Lonapegsomatropin | Growth hormone (weekly) | Skytrofa | about 31 h (prodrug, children) (Skytrofa label) | Weekly injection (label) |
| Tesamorelin | GHRH analog | Egrifta SV, Egrifta WR | 8 to 38 min (by formulation and study) (Egrifta WR label) | Daily injection (label) |
| Sermorelin | GHRH analog | None | 6 to 7 min IV (EU product information) (Geref 50 SPC (HPRA)) | Daily injection in studies |
| CJC-1295 with DAC | GHRH analog | None | 5.8 to 8.1 days (Teichman 2006, JCEM) | Weekly or every other week in studies |
| CJC-1295 without DAC (mod GRF 1-29) | GHRH analog | None | No human value published | No human study published |
| Ipamorelin | Ghrelin-receptor agonist | None | 2 h (IV infusion) (Gobburu 1999, Pharm Res) | Single IV infusions in the human study |
| GHRP-2 | Ghrelin-receptor agonist | None | No human value published | IV test doses in studies |
| GHRP-6 | Ghrelin-receptor agonist | None | 2.5 h (IV) (Cabrales 2013, Eur J Pharm Sci) | IV test doses in studies |
| Hexarelin | Ghrelin-receptor agonist | None | No human value published | IV test doses in studies |
| MK-677 (ibutamoren) | Ghrelin-receptor agonist | None | No human value published | Daily by mouth in studies; GH raised over 24 h |
| Macimorelin | Ghrelin-receptor agonist | Macrilen | 4.1 h (Macrilen label) | One oral dose, as a diagnostic test (label) |
| Mecasermin (rhIGF-1) | IGF-1 | Increlex | 5.8 h (children) (Increlex label) | Twice daily with a meal (label) |
| IGF-1 LR3 | IGF-1 | None | No human value published | No human study published |
Questions people ask about the GH axis
Articles8
- Why tesamorelin pairs with ipamorelin and not with sermorelinTwo receptors, one ceiling, and the combinations no one has tested in people.
- Timing a GH secretagogue: bedtime or before a workout?The body's own GH rhythm, when the studies dosed, and the head-to-head that does not exist.
- Long-acting growth hormones explainedThree once-weekly products, three different ways of making GH last a week.
- Growth hormone vs GH secretagoguesGiving the hormone itself, or asking the pituitary to make more of its own.
- Somatropin brands comparedOne molecule, several names, and which are still on the US market.
- IGF-1 monitoring on GH-axis treatmentWhy IGF-1 is the test, when to draw it on weekly GH, and what the labels say to do with it.
- Tesamorelin and liver fat: what the trials showTwo randomised trials in HIV, registry-only data without HIV, and what neither shows.
- Tesamorelin vs sermorelinSame receptor, different molecule, very different evidence.
Frequently asked questions
Questions
- What is the difference between GH and IGF-1?
- GH is the pituitary hormone; IGF-1 is made mostly by the liver in response to GH and carries much of its growth effect. IGF-1 is the blood test used to monitor GH-axis treatment.
- Which GH-axis drugs have US labels?
- Daily somatropin (several brands), three weekly growth hormones (Sogroya, Ngenla, Skytrofa), tesamorelin (Egrifta SV, WR), mecasermin (Increlex) and the diagnostic macimorelin (Macrilen).
- Are GH-axis agents allowed in sport?
- No. WADA prohibits GH, its analogues, GHRH analogs, growth hormone secretagogues and IGF-1 at all times (S2).
Not medical advice This page summarises published labels and studies. It is not a recommendation to use any product; a clinician decides.