Search "HGH peptides" and the results collapse two very different things into one shopping cart. On one side is somatropin — recombinant human growth hormone, an FDA-approved prescription biologic that a doctor prescribes and a pharmacy dispenses. On the other are the growth-hormone secretagogues — sermorelin, CJC-1295, ipamorelin, tesamorelin, MK-677 and the GHRPs — the research compounds peptide vendors actually stock. They are related in what they influence, but they are not the same category, they are not bought the same way, and they do not do the same thing to the body.
That distinction is the whole point of this comparison. No research-peptide vendor sells somatropin, because it is a regulated drug, not a research chemical. So when someone asks "which peptide is like HGH," the honest answer starts by separating the approved hormone from the compounds that nudge the pituitary to make more of its own. This article lays out what somatropin is and what it is approved for, how the secretagogues take the opposite mechanistic route, and how the two compare on efficacy, access, cost and safety — so the terms stop getting blurred.
Research-context information only. The growth-hormone secretagogues discussed below — sermorelin, CJC-1295, ipamorelin, tesamorelin, MK-677 and the GHRPs — are research peptides, sold for laboratory research use only. Somatropin is a prescription biologic (recombinant human growth hormone) obtained only through a licensed physician; it is described here for education, not as something to source outside that route. Protocols, doses and reactions reported below come from published research and self-reported community sources. This article reports what has been documented, not what should be done. Consult a licensed physician for personal medical decisions.
What Somatropin Actually Is
Somatropin is recombinant human growth hormone: a 191-amino-acid protein manufactured to match the growth hormone the pituitary gland naturally produces. Because it is the finished hormone, an injection raises circulating growth hormone directly and immediately, independent of whether the pituitary would have released any on its own. That is the defining feature — and the defining limitation — of hormone-replacement therapy.
It is approved by the FDA and dispensed only on a prescription. Its labeled indications are specific medical conditions, not general wellness: growth hormone deficiency in children and adults, Turner syndrome, Prader-Willi syndrome, chronic kidney disease in children, short bowel syndrome, and HIV-associated wasting, among others. In adults with diagnosed growth hormone deficiency, the Endocrine Society's clinical practice guideline (Molitch et al., 2011) describes replacement that is individualized and titrated against IGF-1 levels rather than dosed by body weight, and monitored by an endocrinologist. It is a maintenance therapy for a diagnosed deficiency, not an enhancement protocol.
Somatropin is prescription-only for a reason that matters to this comparison. Direct growth hormone bypasses the body's own regulation, so it can push IGF-1 above the physiologic range if not carefully monitored, and distribution outside a legitimate medical channel is tightly restricted under federal law. Peptide vendors do not — and cannot — sell it. That is not a gap in their catalogs; it is the regulatory line that separates an approved drug from a research chemical.
One Name to Untangle: "HGH Fragment 176-191"
Search "HGH peptide" and one product muddies the picture further: HGH Fragment 176-191, which some research vendors do stock. Despite the name, it is not somatropin. It is a short fragment — residues 176 through 191 — of the growth hormone molecule, not the full 191-amino-acid hormone. The distinction is the whole point: the fragment carries a slice of growth hormone's structure without the parts that drive systemic IGF-1 and general growth signaling.
Research on the fragment has centered on lipolysis — fat metabolism — rather than the broad anabolic effects of the intact hormone, which is also why it sits on the research-vendor side of the regulatory line that somatropin does not. The stabilized, modified version most research interest has consolidated around is AOD-9604, an analog of this same fragment. So when a "HGH fragment" listing turns up in a peptide catalog, it belongs to that fat-loss fragment lane, not to recombinant growth hormone — see the AOD-9604 buying guide for the compound that lane actually points to.
Secretagogues Take the Opposite Route
The compounds peptide vendors do sell work on the supply chain rather than the product. A secretagogue is anything that prompts a gland to secrete its own hormone. Growth-hormone secretagogues fall into two families that are often combined in research protocols:
- GHRH analogs — sermorelin, CJC-1295, and tesamorelin — mimic growth-hormone-releasing hormone and signal the pituitary to release growth hormone.
- Ghrelin-receptor agonists (GHRPs and ghrelin mimetics) — ipamorelin, GHRP-6, GHRP-2, hexarelin, and the oral compound MK-677 — act on a second receptor that both triggers a GH pulse and amplifies the GHRH signal.
The mechanistic contrast with somatropin is the crux of the whole comparison. Direct rHGH is a flat, exogenous input; the secretagogues instead provoke the pituitary's own pulsatile release, which remains subject to negative feedback from somatostatin and IGF-1. Teichman and colleagues (2006) documented that a single subcutaneous dose of the long-acting GHRH analog CJC-1295 produced dose-dependent GH increases of roughly 2- to 10-fold and IGF-1 increases of 1.5- to 3-fold in healthy adults, with the elevation persisting for days while natural pulsatility was preserved. That preserved feedback loop is the mechanistic argument researchers make for the secretagogue approach: the pituitary is still in the circuit, so the system retains a ceiling that direct hormone injection removes.
Two of these compounds sit in a middle category worth naming precisely. Sermorelin and tesamorelin are themselves the active ingredients in FDA-approved finished products — sermorelin was historically approved for pediatric growth hormone deficiency and diagnostic testing (Prakash and Goa, 1999), and tesamorelin is approved for HIV-associated lipodystrophy. Their research-peptide and compounded forms, however, are not FDA-approved and are sold for research use only. That makes them a useful bridge: they are GHRH analogs with real clinical trial data behind the molecule, even though the vials a research vendor ships are not the approved product.
Efficacy: What the Trials Actually Measured
The fairest way to compare is to put the trial numbers side by side and let the magnitudes speak, with the mechanism explaining the gap.
Direct rHGH produces the larger body-composition signal. The landmark Rudman study (1990) reported that six months of growth hormone in men over 60 with low baseline IGF-1 was associated with an 8.8% increase in lean body mass, a 14.4% decrease in fat mass, and a small rise in lumbar bone density. Those are substantial shifts — and they came from replacing the hormone outright.
The secretagogue trials report more measured effects, consistent with working through a regulated pathway. Nass and colleagues (2008) gave healthy older adults the oral ghrelin mimetic MK-677 for a year and reported that fat-free mass rose about 1.1 kg versus a 0.5 kg decline on placebo, while GH and IGF-1 were restored toward young-adult levels without serious adverse effects in that cohort. For tesamorelin, Stanley and colleagues (2014) reported in a randomized trial that daily injection over six months reduced visceral adipose tissue and liver fat in HIV-infected patients with abdominal fat accumulation — a targeted fat-depot effect rather than a whole-body recomposition claim.
The pattern across these trials is consistent: direct hormone replacement moved the larger numbers, and the secretagogues moved smaller, physiology-bounded numbers while keeping the pituitary in control. Neither the trial literature nor community sources support framing any secretagogue as mechanically equivalent to injected rHGH. They influence the same axis through different doors, and the reported effect sizes reflect that.
Affiliate disclosure: the vendor links below and throughout this article are monetized — The Peptide Catalog earns a commission on purchases made through them. Somatropin is a prescription drug and is not among them.
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