Somatropin vs sermorelin
Last updated: October 3, 2026 · 6 min read · By the Grey Peptides Editorial Board
- Somatropin is growth hormone itself. Sermorelin is a fragment of the hypothalamic hormone that tells the pituitary to release growth hormone, so it only works if the pituitary can respond.
- Somatropin is approved for many conditions on the strength of large trials and decades of follow-up. Sermorelin was approved in the US as Geref for children with growth hormone deficiency and has been discontinued.
- Neither is approved for anti-ageing or bodybuilding, and a meta-analysis of growth hormone in healthy older adults found small body-composition changes and frequent side effects.
Side by side
Somatropin High and sermorelin Medium both act on the growth hormone system, from opposite ends. The table is read from our encyclopedia entries.
| Field | Somatropin (HGH) | Sermorelin |
|---|---|---|
| Encyclopedia entry | Somatropin (HGH) Full entry | Sermorelin Full entry |
| Molecule class | Protein, not a peptide | Peptide |
| Category | Growth Hormone | Growth Hormone |
| FDA status | FDA Approved | Discontinued |
| Approved elsewhere | None recorded | None recorded |
| Evidence grade | High | Medium |
| Half-life | ≈ 3.5 hours | Not established in our sources |
| Formula | C990H1528N262O300S7 | C149H246N44O42S |
| Molecular weight | 22,124.0 g/mol | 3,357.9 g/mol |
| WADA 2026 | Prohibited at all times (S2.2.3) | Prohibited at all times (S2.2.4) |
| WADA 2027 | Prohibited at all times (S2.2.3) | Prohibited at all times (S2.2.4) |
| In one line | FDA-approved recombinant human growth hormone — the direct hormone replacement, with multiple clinical indications, prescription-only status, and specific federal criminal provisions against off-label distribution. | GHRH's first 29 amino acids, sold in the US as Geref (approved 1990 and 1997) to test and treat childhood growth hormone deficiency until it was discontinued, not for safety reasons. |
| Mechanism | Binds dimerized GH receptors on target tissues, triggering JAK2/STAT5 signaling. Direct effects include lipolysis (adipocyte), gluconeogenesis and insulin antagonism (hepatic), and anabolic effects on muscle, bone, and cartilage. Indirect effects are mediated by hepatic IGF-1 production, which drives most of the somatic growth effects. Exogenous administration suppresses endogenous pulsatile secretion via negative feedback on hypothalamic somatostatin and GHRH neurons. | GHRH receptor agonist: the 29-amino-acid active fragment of GHRH, which stimulates growth hormone secretion from the anterior pituitary. Used as a 1 µg/kg intravenous test of pituitary reserve (a normal response cannot exclude hypothalamic deficiency) and, as Geref, as a nightly treatment for children with idiopathic growth hormone deficiency. |
| Sources in the entry | 13 | 9 |
| Study cards | 8 | 6 |
| Dosage page | None | Dosage page |
The hormone and its releasing signal
Growth hormone is made by the pituitary gland, and its release is driven by growth-hormone-releasing hormone (GHRH) from the hypothalamus. Somatropin is recombinant human growth hormone, the 191-amino-acid protein itself, made in cells and injected. It bypasses the pituitary entirely: whatever dose is given is what the body receives, whether or not the pituitary works 1.
Sermorelin is GHRH(1-29), the first 29 amino acids of GHRH, which carry its activity. It does not contain growth hormone. It stimulates the pituitary to release its own, so its effect depends on a pituitary that can respond, and the body's own feedback systems still limit how much is released 1. That difference explains most of what follows: somatropin can treat deficiency caused by pituitary damage; sermorelin cannot.
Somatropin's evidence
Somatropin has one of the deepest evidence bases of any peptide or protein drug. In a randomised trial in 154 Canadian girls with Turner syndrome, growth hormone raised adult height compared with observation 2. A Growth Hormone Research Society consensus drew on more than 30 controlled studies in Prader-Willi syndrome 3. Long-acting versions have been tested in phase 3 trials, such as weekly lonapegsomatropin against daily somatropin in 161 children with growth hormone deficiency 4. Long-term safety has been studied in 24,232 European patients treated in childhood and followed for up to 25 years 5. Its approved uses run from childhood growth hormone deficiency to adult deficiency and several genetic conditions 1.
What somatropin has not been shown to do is reverse ageing. A meta-analysis of 18 randomised trials of growth hormone in healthy older adults found small changes in body composition, with more fat lost and lean mass gained, but no clear gains in strength or fitness and higher rates of side effects such as swelling, joint pain and carpal tunnel syndrome 6.
Sermorelin's evidence
Sermorelin's human evidence is older and smaller. As an intravenous test, a review described it as a rapid and relatively specific way to diagnose growth hormone deficiency in children, with fewer false positives than other stimulation tests 7. In children with short stature, it raised growth hormone promptly when given as a nasal spray 8, and six days of injections restored the growth hormone response in some children who had not responded to a first test 9. FDA approved it as Geref for the diagnosis and treatment of idiopathic growth hormone deficiency in children; both Geref products were later discontinued 1.
The large modern trials that somatropin has do not exist for sermorelin, and it has not been tested for the adult uses it is now marketed for, such as anti-ageing, sleep or body composition. A 1990 study in 23 healthy young adults found better word recall two hours after an intravenous dose 10, a single small experiment, not a basis for treatment.
Why sermorelin is marketed as a 'gentler' alternative
Since Geref's discontinuation, sermorelin has been offered by compounding pharmacies and wellness clinics, often as a 'natural' way to raise growth hormone with fewer risks than somatropin. The logic is that because the pituitary's feedback limits release, sermorelin cannot push growth hormone as high. That is plausible as physiology, but it is not the same as evidence of benefit or safety in adults, which has not been established in modern trials. Our sermorelin guide covers its history and current use in more detail.
Safety
Somatropin's side effects are well characterised; in healthy older adults they included swelling, joint pain and carpal tunnel syndrome, and its long-term safety in treated children has been studied over decades 5 6. Sermorelin's safety record is much thinner: its trials were small and short, mostly in children, and it has not been studied for long periods in adults 1. Both are prohibited at all times by WADA 1.
How the differences add up (as of October 3, 2026)
For a person with diagnosed growth hormone deficiency, somatropin is the established, approved treatment, and it works whether or not the pituitary does. Sermorelin was an approved option for some children decades ago and no longer is; its modern use in adults rests on physiology rather than trials. Neither is approved or proven for anti-ageing. Any decision about either belongs with an endocrinologist after proper testing.
Frequently asked questions
Is sermorelin the same as HGH?
No. Somatropin is human growth hormone itself; sermorelin is a fragment of the hormone that signals the pituitary to release growth hormone, so it depends on a working pituitary.
Is sermorelin FDA-approved?
It was approved in the US as Geref for the diagnosis and treatment of idiopathic growth hormone deficiency in children, and both Geref products were discontinued.
Which is safer, sermorelin or somatropin?
Somatropin's safety is well documented from decades of trials and follow-up. Sermorelin has much less long-term data, especially in adults, so it cannot be called safer on the evidence.
Related on Grey Peptides
Sources
- Grey Peptides dataset records for somatropin and sermorelin (approval details, status, half-life and studied doses as sourced on each entry); read October 3, 2026.
- Stephure, D. K. (2005). Impact of growth hormone supplementation on adult height in turner syndrome: results of the Canadian randomized controlled trial. J Clin Endocrinol Metab, 90(6), 3360-6. PMID: 15784709
- Deal, C. L., et al. (2013). GrowthHormone Research Society workshop summary: consensus guidelines for recombinant human growth hormone therapy in Prader-Willi syndrome. J Clin Endocrinol Metab, 98(6), E1072-87. PMID: 23543664
- Thornton, P. S., et al. (2021). Weekly Lonapegsomatropin in Treatment-Naïve Children With Growth Hormone Deficiency: The Phase 3 heiGHt Trial. J Clin Endocrinol Metab, 106(11), 3184-3195. PMID: 34272849
- Sävendahl, L., et al. (2020). Long-term mortality after childhood growth hormone treatment: the SAGhE cohort study. Lancet Diabetes Endocrinol, 8(8), 683-692. PMID: 32707116
- Liu, H., et al. (2007). Systematic review: the safety and efficacy of growth hormone in the healthy elderly. Ann Intern Med, 146(2), 104-15. PMID: 17227934
- Prakash, A., et al. (1999). Sermorelin: a review of its use in the diagnosis and treatment of children with idiopathic growth hormone deficiency. BioDrugs, 12(2), 139-57. PMID: 18031173
- Borkenstein, M. (1986). The effects of intranasal insufflation of growth hormone releasing factor analogue GRF 1-29 NH2 on growth hormone secretion in children with short stature. Acta Endocrinol Suppl (Copenh), 279, 135-8. PMID: 2877535
- Bueno, G., et al. (1994). Priming with GHRH (1-29) NH2: an aid in differential diagnosis between hypothalamic and pituitary deficiencies. J Pediatr Endocrinol, 7(4), 309-16. PMID: 7735368
- Alvarez, X. A., et al. (1990). Effects of GRF (1-29) NH2 on short-term memory: neuroendocrine and neuropsychological assessment in healthy young subjects. Methods Find Exp Clin Pharmacol, 12(7), 493-9. PMID: 2087150
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