Ipamorelin vs Sermorelin: A Canadian Research Comparison of Two Growth Hormone Secretagogues

The comparison between Ipamorelin and Sermorelin is one of the most practically important distinctions in the growth hormone peptide research space, and also one of the most frequently blurred. Both compounds are marketed as growth hormone secretagogues. Both appear in supplier catalogues under the same broad heading. Both claim to increase GH levels. Because they share a functional endpoint, they are often grouped together as though they were variants of the same mechanism or interchangeable tools in the same protocol. They are not.

Sermorelin is a synthetic analogue of growth hormone releasing hormone (GHRH), truncated to the 29 amino acid N-terminal fragment that retains full biological activity at the GHRH receptor. It belongs to the releasing-hormone family, alongside CJC-1295, Tesamorelin, and GHRH itself. Ipamorelin is a synthetic pentapeptide belonging to the growth hormone releasing peptide (GHRP) family, alongside GHRP-2, GHRP-6, and Hexarelin. It is a selective agonist at the ghrelin receptor (GHS-R1a), which is expressed on pituitary somatotrophs and in hypothamic circuits that regulate appetite, energy balance, and circadian GH pulsatility.

The two molecules do not compete for the same receptor. They do not produce the same intracellular signalling pattern. They do not replicate the same pulse dynamics. They do not have the same regulatory history, the same evidence base, or the same side-effect profile in published work. For a Canadian researcher designing a protocol around GH physiology, conflating them is a methodological mistake that can invalidate the experimental question before the first assay is run.

This comparison is written for Canadian researchers who need to decide which compound belongs in a given study, or whether both should be used in combination. It is not a consumer buying guide, a dosing manual, or a wellness recommendation. Nothing here is medical advice. The purpose is to separate the two molecules clearly, compare their evidence bases honestly, and give researchers a defensible framework for choosing between them—or for understanding why the combined GHRH-plus-GHRP protocol produces effects that neither compound produces alone.

A fast summary before the details#

If a Canadian researcher needs the short version before the full comparison:

• Sermorelin is a GHRH-receptor agonist. Its mechanism is additive to the natural GHRH signal from the hypothalamus. It augments GH pulse amplitude, is well characterised in diagnostic and paediatric endocrinology literature, and has a regulatory history (though no longer marketed as a drug in the United States). It is the closer tool when the research question is about GHRH-receptor pharmacology, GH-deficiency models, or endogenous-axis restoration.

• Ipamorelin is a GHS-R1a (ghrelin receptor) agonist. Its mechanism is complementary to GHRH: it increases the number of GH pulses, potentiates GHRH-induced release, and operates through a different second-messenger system (PLC/PKC/Ca²⁺ rather than cAMP/PKA). It is the closer tool when the research question is about ghrelin biology, pulse-frequency modulation, appetite circuitry, or the distinction between GH release and cortisol/prolactin co-release.

• Used together, GHRH analogues and GHRPs produce synergistic GH release that is greater than the sum of either alone. This synergy is a consistent finding across preclinical and human studies and is one of the best-established facts in the GH-secretagogue literature.

• Neither compound is interchangeable with recombinant human GH (somatropin). Recombinant GH bypasses the pituitary entirely and directly elevates circulating IGF-1. Secretagogues stimulate the endogenous GH pulse generator, which produces variable GH and IGF-1 responses depending on age, sex, nutritional status, sleep, and feedback sensitivity. These are different experimental variables and should not be treated as equivalent.

If you are comparing supplier pages#

This article is not a buying recommendation, but comparison readers usually arrive with product tabs already open. Treat the product page as a documentation checkpoint, not as a protocol. For single-compound work, start by comparing the current COA, sequence identity, fill amount, and RUO language for Ipamorelin and Sermorelin. If the question is a dual-receptor GH-secretagogue model, compare that single-vial approach with a documented CJC-1295 and Ipamorelin blend and the separate CJC-1295 without DAC page before assuming the blend's fixed ratio fits the study.

For deeper routing, use the CJC-1295 and Ipamorelin guide when the search intent is specifically about blends, the best growth hormone peptides in Canada page when the reader needs a category-level shortlist, and the growth hormone peptide stacks guide when the research question is about combining GHRH-side and GHRP-side materials. Those internal guides keep the conversion path research-use-only and COA-first instead of turning this comparison into dosing advice.

COA-first product shortlist for this comparison#

If the comparison has moved from mechanism review to supplier due diligence, keep the shortlist narrow. For a clean two-arm study, document Sermorelin against Ipamorelin and confirm that each current lot has HPLC purity, mass-spectrometry identity, stated fill amount, storage guidance, and explicit research-use-only language. For a combination model, compare separate vials with the documented CJC-1295 and Ipamorelin blend; the blend may simplify procurement, but it also fixes the ratio and removes independent titration as an experimental variable.

For adjacent designs, route outward instead of forcing every GH-axis question into this binary. Use the Ipamorelin Canada guide for GHS-R1a-specific endpoints, the Sermorelin Canada guide for GHRH-fragment pharmacology, and the where to buy Ipamorelin in Canada research guide or where to buy Sermorelin in Canada research guide when the next step is supplier documentation rather than mechanism selection. Product links on Northern Compound may include attribution parameters for Lynx Labs; readers should still verify the live batch COA before any research purchase.

If the comparison expands from Sermorelin into a modified GHRH fragment, send that sourcing decision to the where to buy CJC-1295 without DAC in Canada research checklist. It keeps the no-DAC Modified GRF record separate from both Sermorelin and Ipamorelin, which matters when a study depends on receptor lane, half-life, and independent COA traceability.

Structural lineage: two families, one axis#

The growth hormone axis is regulated at multiple levels. The highest level is the hypothalamus, where GHRH neurons and somatostatin neurons compete to set GH pulse timing. GHRH stimulates GH release; somatostatin inhibits it. The resulting pattern is episodic: GH rises in discrete pulses, largely during slow-wave sleep and in response to exercise, stress, and nutritional cues.

At the pituitary level, somatotroph cells express both the GHRH receptor and the ghrelin receptor (GHS-R1a). GHRH binds its receptor and activates the cAMP/PKA pathway, increasing intracellular calcium and driving GH exocytosis. Ghrelin and its mimetics bind GHS-R1a and activate the PLC/PKC pathway, also increasing calcium but through IP₃-mediated release from intracellular stores and voltage-gated calcium channel opening. The two pathways converge on GH secretion but arrive there through different molecular machinery.

Sermorelin occupies the GHRH-receptor side of this map. It was developed by replacing the first 29 amino acids of human GHRH with a synthetic fragment that retains full receptor affinity. Ipamorelin occupies the GHS-R1a side. It was developed as part of a systematic effort to find smaller peptides that could activate the ghrelin receptor with high selectivity for GH over other pituitary hormones.

Understanding that lineage matters because supplier catalogues often file both compounds under "growth hormone peptides" without distinguishing receptor families. A researcher who orders Ipamorelin thinking it is "like Sermorelin but newer" or orders Sermorelin thinking it is "the natural option compared to Ipamorelin" is operating with a categorisation error that distorts experimental design.

Sermorelin: the GHRH fragment#

Sermorelin corresponds to human GHRH(1-29)-NH₂, the minimal sequence required for full biological activity at the GHRH receptor. The full-length GHRH peptide is 44 amino acids, but the C-terminal residues beyond position 29 do not add receptor affinity in most species. Sermorelin therefore acts as a high-potency, shorter synthetic substitute.

The GHRH receptor is a Gs-coupled seven-transmembrane receptor. Activation increases adenylyl cyclase activity, raises cAMP, activates protein kinase A (PKA), and phosphorylates proteins involved in vesicular trafficking and calcium handling. The net effect is an increase in GH pulse amplitude: the same pulses occur on roughly the same schedule, but the amount of GH released per pulse is larger.

Sermorelin has been studied extensively in diagnostic endocrinology. The Sermorelin stimulation test was once a standard method for evaluating GH deficiency in children and adults. Intravenous or subcutaneous Sermorelin produces a rapid, dose-dependent rise in serum GH that peaks within 30–60 minutes. The test is sensitive to pituitary reserve: a robust response indicates intact somatotroph function, while a blunted response suggests deficiency.

The clinical literature on Sermorelin is larger and older than the literature on Ipamorelin. That gives Sermorelin an advantage in terms of established pharmacokinetics, safety profiles, and regulatory familiarity. It also means that much of the evidence was generated in paediatric and diagnostic contexts, which are not always directly transferable to adult research models.

Ipamorelin: the selective ghrelin mimetic#

Ipamorelin is a pentapeptide with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH₂. It was developed in the late 1990s as a selective agonist at the growth hormone secretagogue receptor (GHS-R1a), the same receptor activated by the endogenous hormone ghrelin.

Ghrelin was identified in 1999 as the endogenous ligand for the orphan receptor GHS-R. It is produced primarily in the stomach and is the only known circulating orexigenic hormone. Beyond appetite, ghrelin potently stimulates GH release from pituitary somatotrophs, raises prolactin and ACTH/cortisol to a lesser degree, and influences sleep, mood, reward circuitry, and glucose homeostasis.

Ipamorelin was designed to retain the GH-releasing potency of ghrelin while improving selectivity. Early preclinical studies reported that Ipamorelin released GH in a dose-dependent manner in rats and pigs, with minimal effects on prolactin, ACTH, and cortisol compared with GHRP-2 and GHRP-6. That selectivity profile was a primary development goal: earlier GHRPs were known to raise cortisol and prolactin substantially, limiting their clinical appeal.

The GHS-R1a receptor couples to Gq/11 and activates phospholipase C, producing IP₃ and diacylglycerol. IP₃ releases calcium from intracellular stores; diacylglycerol activates protein kinase C. The resulting calcium signal is distinct from the cAMP-driven mechanism of GHRH, and the two pathways synergise when co-activated: GHRH primes the somatotroph, and ghrelin mimetics provide the calcium trigger that amplifies exocytosis.

This synergy is one of the most robust findings in the secretagogue literature. In vitro studies on rat pituitary cells, in vivo rodent studies, and human clinical studies all show that combined GHRH plus GHRP produces a GH response that is larger than the arithmetic sum of the individual responses. The mechanism is well understood: the two receptors act on different but convergent signalling nodes, and their co-activation produces supra-additive calcium signalling and vesicular release.

Mechanism in depth: cAMP/PKA vs. PLC/PKC, and why the difference matters#

For a researcher designing an endpoint assay, the signalling distinction is not academic. It determines which downstream variables will be affected and which will not.

Sermorelin: cAMP, PKA, and amplitude augmentation#

When Sermorelin binds the GHRH receptor, the Gs protein activates adenylyl cyclase. cAMP rises, PKA is activated, and the catalytic subunit of PKA phosphorylates voltage-gated calcium channels (increasing calcium influx) and proteins involved in vesicle docking and fusion. The net effect is an increase in the amount of GH released per secretory event.

Importantly, GHRH also stimulates somatotroph proliferation and GH gene transcription. Chronic GHRH exposure increases somatotroph number and GH mRNA levels in animal models. This transcriptional effect is mediated by CREB phosphorylation and is part of why GHRH deficiency leads not only to low GH secretion but also to reduced somatotroph mass.

Sermorelin, as a GHRH analogue, reproduces these transcriptional effects at the receptor level. A researcher studying somatotroph biology, pituitary histology, or GH gene regulation should therefore consider whether the experimental model requires acute secretion only or also chronic cellular adaptation. Sermorelin is the more appropriate tool for the latter question; Ipamorelin has minimal direct transcriptional effect on GH synthesis.

Ipamorelin: IP₃, DAG, PKC, and frequency augmentation#

Ipamorelin binding to GHS-R1a activates PLC-β, producing IP₃ and DAG. IP₃ binds its receptor on the endoplasmic reticulum, releasing stored calcium. DAG activates PKC, which phosphorylates proteins that modulate vesicle priming and calcium sensitivity. Additional calcium enters through voltage-gated channels opened by depolarisation.

The result is a different pattern of GH secretion. GHS-R1a activation does not just augment existing pulses; it can initiate new pulses, increase pulse frequency, and shift the timing of GH release relative to sleep and circadian cues. This is because GHS-R1a is expressed in hypothalamic neurons that regulate GHRH and somatostatin release, not only on pituitary somatotrophs. Ghrelin mimetics therefore act at both the hypothalamic and pituitary levels, creating a more complex and distributed signal.

That distributed action is experimentally relevant. If a protocol is designed to study hypothalamic pulse-generator function, appetite-GH coupling, or the integration of metabolic and reproductive signals, Ipamorelin is the closer tool. If the protocol is designed to study pituitary reserve, GHRH-receptor pharmacology, or somatotroph transcriptional responses, Sermorelin is the closer tool.

Evidence map: what the literature actually says#

A responsible comparison separates the evidence by species, endpoint, and regulatory context. Collapsing preclinical rat data with human clinical data produces false confidence. Treating Sermorelin's paediatric diagnostic history as equivalent to Ipamorelin's selectivity profile produces false equivalence.

Sermorelin evidence#

Diagnostic endocrinology. Sermorelin was approved by the FDA in 1997 as a diagnostic agent for evaluating GH deficiency in children and as a treatment for idiopathic GH deficiency. It was withdrawn from the US market in 2008 for commercial reasons, not because of safety concerns. The paediatric literature includes multiple studies showing growth acceleration in GH-deficient children treated with subcutaneous Sermorelin. Adult studies are sparser but include growth hormone stimulation tests and small trials in age-related GH decline.

Pharmacokinetics. Subcutaneous Sermorelin produces a rapid rise in serum GH, peaking at 30–60 minutes and returning toward baseline by 2–3 hours. The peptide is cleared by renal filtration and proteolysis, with a plasma half-life estimated at 10–20 minutes. This short half-life is why multiple daily injections or continuous infusion were required in therapeutic protocols, and why long-acting analogues such as CJC-1295 with DAC were developed.

Safety profile. The safety literature from paediatric use is relatively reassuring: local injection-site reactions, flushing, and headache are the most commonly reported adverse effects. Because Sermorelin stimulates endogenous GH release rather than bypassing the axis, feedback inhibition via IGF-1 and somatostatin limits excessive GH elevation in most subjects. The risk of acromegaly, leptin resistance, or uncontrolled IGF-1 rise is therefore lower than with exogenous GH, though not zero in susceptible individuals.

Limitations. The main limitation for adult research is that Sermorelin's short half-life makes it less convenient for chronic protocols than long-acting analogues. Its GH-releasing potency is also lower per microgram than some synthetic alternatives. For research protocols requiring sustained GH elevation over 24 hours, CJC-1295 or other modified GHRH analogues may be more suitable. Sermorelin is best viewed as the reference compound for GHRH-receptor pharmacology rather than the most potent tool for every GH-related question.

Ipamorelin evidence#

Preclinical selectivity. The most cited Ipamorelin paper is the 1998 study by Raun et al. in Endocrinology, which reported that Ipamorelin released GH in a dose-dependent manner in rats and pigs, with a potency similar to GHRP-6 but with markedly reduced effects on cortisol, prolactin, ACTH, aldosterone, and TSH. This selectivity profile was described as a major advance because earlier GHRPs raised cortisol and prolactin substantially, producing side-effect profiles that complicated clinical development.

Human pharmacology. Human data on Ipamorelin are limited compared with Sermorelin. Published studies include small Phase I trials and pharmacodynamic studies in healthy volunteers. One human study reported dose-dependent GH release after intravenous Ipamorelin, with a short half-life and rapid clearance. Another examined the combined effect of Ipamorelin and GHRH, confirming the synergistic interaction predicted by preclinical models. At the time of writing, Ipamorelin has not received FDA or Health Canada approval for any therapeutic indication.

Mechanistic relevance. Ipamorelin's value in research is not primarily clinical; it is mechanistic. It is one of the most selective tools available for studying GHS-R1a signalling in isolation from other GHRP receptors or from the broader hormonal effects of ghrelin itself. Because ghrelin also targets motilin receptors, corticotrophs, and central reward circuits, using the endogenous hormone as a research tool introduces confounds that Ipamorelin avoids.

Limitations. The principal limitation is the thinness of the human evidence base. Preclinical rat and pig data are informative but do not automatically translate to human somatotroph pharmacology. The short half-life is similar to Sermorelin, requiring multiple injections for sustained protocols. And while Ipamorelin's selectivity for GH over cortisol and prolactin is better than GHRP-2 or GHRP-6, the absolute magnitude of that selectivity in humans is less well quantified than in animals.

The synergy question: why GHRH plus GHRP produces more than the sum#

If the comparison were limited to Sermorelin vs. Ipamorelin individually, the choice would be simpler. But growth hormone research often involves combined protocols, and the synergy between GHRH analogues and GHRPs is one of the best-supported findings in the field.

Multiple rodent studies have shown that co-administration of GHRH and GHRP produces a GH response that is approximately additive to synergistic, depending on dose and timing. In vitro work on dispersed rat pituitary cells showed that GHRP-6 and GHRH together produced more GH than the sum of either alone, and that the synergy depended on intracellular calcium signalling.

Human studies confirm the principle. Combined GHRH and GHRP administration in healthy adults produces GH responses that are large, reproducible, and greater than either peptide alone. This is the rationale behind the widely used GH secretagogue test in endocrinology: GHRH plus arginine (or GHRP-6, where available) is one of the most sensitive ways to assess somatotroph reserve.

For Canadian researchers, the practical implication is that a protocol using Sermorelin and Ipamorelin together is not simply "double the GH." It is a mechanistically distinct state: co-activation of cAMP/PKA and PLC/PKC pathways, convergence on enhanced calcium signalling, and amplification of both pulse amplitude and pulse frequency. Any study comparing single-agent vs. combined protocols should measure endpoints that can distinguish these mechanisms—such as GH pulse frequency (measured by frequent sampling), IGF-1 trajectory (reflecting chronic exposure), and somatostatin response (reflecting feedback integrity).

Side-effect and safety profiles from a research perspective#

Neither peptide is approved by Health Canada as a medicine when sourced through research-supply channels. Both are research-use-only materials. The safety profiles discussed below are drawn from published literature and regulatory documents, not from clinical prescribing experience in Canada.

Sermorelin#

The paediatric diagnostic and therapeutic literature is the largest safety dataset. Common reported effects include injection-site erythema, headache, flushing, and transient hyperglycaemia. Anti-GHRH antibodies were rarely reported in long-term use but were described in some paediatric cohorts. The immune response did not appear to neutralise efficacy in most cases.

Because Sermorelin stimulates the endogenous axis, GH and IGF-1 elevations are feedback-limited. This is generally considered safer than exogenous GH, where dose escalation can override feedback and produce uncontrolled IGF-1 rises. However, in individuals with pituitary adenomas or other intracranial pathology, any GH secretagogue could theoretically promote unwanted growth. Contraindications included intracranial lesions and closed epiphyses in children.

Ipamorelin#

The human safety dataset is smaller. Preclinical toxicology in rats and dogs showed no significant organ toxicity at doses producing GH elevations. Human Phase I data reported no serious adverse events at tested doses. The most common effects were mild injection-site discomfort and transient flushing.

Because Ipamorelin is more selective than GHRP-2 and GHRP-6, the cortisol and prolactin elevations seen with older GHRPs are expected to be smaller. This is a theoretical advantage, though the magnitude of the difference in chronic human use is not well characterised. The cardiovascular effects of ghrelin-receptor agonism—heart rate, blood pressure, and vascular tone—are areas of ongoing research and should be considered in any protocol measuring cardiometabolic endpoints.

Comparative safety#

For research purposes, both compounds are best characterised as "endogenous-axis stimulators" rather than "direct hormone replacements." That framing carries a safety advantage: the pituitary's feedback mechanisms can partially blunt excessive GH release. It also carries a research complexity: inter-individual variability in GH response will be large, and control-group design must account for baseline age, sex, BMI, sleep quality, and nutritional status.

A researcher running a combined Sermorelin-plus-Ipamorelin protocol should be especially attentive to the synergistic GH peak. While the GH response to either agent alone is usually within the physiological range, the combined response can be substantially larger. Protocol safety monitoring should include IGF-1, fasting glucose, and insulin sensitivity markers if the model allows.

When to choose which: an experimental decision framework#

The choice between Sermorelin and Ipamorelin should be driven by the research question, not by supplier marketing or compound novelty.

Choose Sermorelin when:

• The question is about GHRH-receptor pharmacology, cAMP/PKA signalling, or somatotroph transcriptional responses.
• The endpoint is GH pulse amplitude augmentation.
• The model involves GH-deficiency replacement or diagnostic stimulation testing.
• A well-characterised regulatory history and larger clinical dataset are valued for protocol design or grant justification.
• The study duration benefits from a reference compound with established paediatric and adult pharmacokinetics.

Choose Ipamorelin when:

• The question is about ghrelin-receptor signalling, GHS-R1a selectivity, or appetite-energy-GH integration.
• The endpoint is GH pulse frequency, novel pulse initiation, or hypothalamic-pituitary integration.
• The protocol requires a selective GH secretagogue with minimal direct cortisol or prolactin co-release.
• The study compares receptor families (GHRH vs. ghrelin) or tests synergy hypotheses.
• The researcher wants a compound that can be combined with a GHRH analogue to model the physiological dual-receptor activation of the GH axis.

Consider the combination when:

• The research question explicitly involves the dual-receptor synergy that characterises natural GH physiology.
• The endpoint requires maximal GH release within a defined window (e.g., stimulation testing, pulse-generation research).
• The protocol is designed to compare single-agent vs. combined effects, with mechanistic endpoints that can distinguish amplitude from frequency.
• The protocol is explicitly built around a documented GHRH-plus-GHRP combination, and the researcher accepts the fixed-ratio limitation if using any pre-formulated blend.

The fixed-ratio limitation is worth emphasising. A blended product fixes the molar ratio of the two compounds. In research, that ratio may not be optimal for every model. Individual vials of Ipamorelin and Sermorelin allow independent titration, whereas a blend simplifies logistics at the cost of experimental flexibility. The choice between a documented blend and individual compounds is a research-design decision, not a convenience decision. Northern Compound does not treat unavailable or undocumented blended SKUs as live product recommendations.

Sourcing, quality control, and Canadian context#

What a COA should prove#

For both Sermorelin and Ipamorelin, the minimum documentation standard is the same:

1. Identity: Declared sequence, confirmed by mass spectrometry. For Sermorelin, the expected molecular weight of the acetate or free-base form should be stated. For Ipamorelin, the amidated pentapeptide mass should be confirmed.
2. Purity: Lot-matched HPLC with chromatogram, showing a major peak at ≥98% area and resolved minor peaks.
3. Salt and counterion: Clear disclosure (acetate, trifluoroacetate, HCl, or free base), because this affects mass calculations.
4. Fill amount: Mass per vial, not merely "X mg" without specification of peptide content vs. total salt mass.
5. Storage and stability: Lyophilised storage temperature, light/moisture protection, and reconstitution stability guidance.
6. Research-use-only language: Explicit statement that the product is for research and not for human consumption, diagnostic, or therapeutic use.

Canadian regulatory framing#

Health Canada does not list Sermorelin or Ipamorelin as controlled substances. They are available for research purposes through specialised Canadian suppliers. The legal boundary is the intended use: research is permissible; marketing as a medicine, wellness product, or performance enhancer is not.

Northern Compound's position is that both compounds should be sourced with full batch documentation and handled with the same rigour as any other research peptide. See the Canadian researcher's guide to buying research peptides for a detailed framework on evaluating suppliers, reading COAs, and understanding the regulatory environment.

Storage and handling#

Both Sermorelin and Ipamorelin are supplied as lyophilised powders and should be stored at −20°C in a desiccated environment, protected from light and moisture. Reconstitution, if required by the protocol, should use bacteriostatic water or the vehicle specified in the literature, with attention to pH, osmolality, and shelf-life after reconstitution. The reconstitution guide covers these principles in detail.

Because both peptides are small (29 and 5 residues respectively), they are relatively stable as lyophilisates but can degrade rapidly if exposed to moisture, heat, or repeated freeze-thaw cycles. Vials should be inspected for caking, discoloration, or dissolution before use. Any change in appearance from the documented standard is grounds for replacement.

Relationship to neighbouring compounds#

The growth hormone archive on Northern Compound includes several compounds that intersect with Sermorelin and Ipamorelin.

CJC-1295 with DAC and CJC-1295 without DAC are modified GHRH analogues with extended half-lives. They occupy the same receptor family as Sermorelin but offer different pharmacokinetic profiles. Researchers comparing product documentation can review CJC-1295 with DAC beside CJC-1295 without DAC, then use the CJC-1295 DAC vs. no-DAC comparison to interpret the trade-offs.

Tesamorelin is a stabilised GHRH analogue with FDA approval for HIV-associated lipodystrophy. It is structurally related to Sermorelin but has a longer plasma half-life and a different clinical indication.

GHRP-2 and GHRP-6 are earlier-generation ghrelin mimetics with less selectivity than Ipamorelin. They raise cortisol and prolactin more substantially and are useful comparator compounds in selectivity studies.

HGH is recombinant human growth hormone. It bypasses the pituitary and directly elevates circulating GH. Comparing secretagogue protocols to exogenous GH protocols is a common and important experimental design question, but HGH should be treated as a separate control-path candidate, not as an interchangeable substitute for either secretagogue.

Summary: the comparison table#

The table simplifies a complex comparison, but it captures the essential distinction. Sermorelin is the reference GHRH-receptor agonist with a paediatric diagnostic history and a well-understood amplitude-driven mechanism. Ipamorelin is the selective ghrelin mimetic with a frequency-driven mechanism and a cleaner selectivity profile than its GHRP predecessors. For many research questions, the better answer is not either/or but both, because natural GH physiology is governed by the interplay of both receptor systems.

Selected research and regulatory references#

• Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999.
• Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. Endocrinology. 1998.
• Mayo KE, Miller LJ, Bataille D, et al. International Union of Pharmacology. XXXV. The glucagon receptor family. Pharmacological Reviews. 2003. Includes GHRH-receptor family context.
• Bowers CY, Momany FA, Reynolds GA, Hong A. On the in vitro and in vivo activity of a new synthetic hexapeptide that acts on the pituitary to specifically release growth hormone. Endocrinology. 1984. Foundational growth-hormone secretagogue work.
• U.S. FDA Orange Book discontinued-drug data files are useful for confirming whether historical products are currently marketed before extrapolating from old regulatory language.
• Health Canada. Drug product database. Useful for confirming whether a peptide is authorised as a Canadian drug product before interpreting research-supply claims.