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Ghrelin28 residuesGSSFLSPEHQRVQQRKESKKPPAKLQPREach bubble = one amino acid. Size = residue mass. Color = chemical class.Also known as: GHRL, lenomorelin, hunger hormone
Over 10,000 published studies on PubMed. That puts ghrelin among the most researched peptide hormones in endocrinology. This 28-amino-acid molecule, discovered in 1999, is the only known circulating hormone that tells your brain to eat. It also triggers growth hormone release through the GHS-R1a receptor. The catch: native acylated ghrelin degrades in under 13 minutes after IV administration. Plasma esterases strip the octanoyl modification almost immediately. Clinical trials in cancer cachexia showed 1 to 3 kg of weight gain over 4 to 8 weeks (Lundholm et al.)[1]. Most people chasing ghrelin receptor effects turn to GHRP-2, GHRP-6, or MK-677 instead.
Twenty-eight amino acids with a fatty acid tail that breaks every rule. Ghrelin (CAS 258279-04-4) was identified in 1999 by Kojima and colleagues as the endogenous ligand for the growth hormone secretagogue receptor GHS-R1a [2]. The octanoyl group attached to Ser3 by ghrelin O-acyltransferase (GOAT) is what makes the molecule bind its receptor. Without that lipid tag, ghrelin is biologically inactive at GHS-R1a. The stomach produces ghrelin in gastric oxyntic cells. Levels rise before meals and fall after eating. When ghrelin reaches the hypothalamus, it activates NPY/AgRP neurons and suppresses the satiety pathway (POMC/CART signaling). The result is a strong hunger signal. At the pituitary, it triggers growth hormone release through a calcium-dependent pathway independent of GHRH. That dual action, appetite plus GH secretion, made it a therapeutic candidate for cancer cachexia and wasting diseases. Clinical data backs this up. Lundholm and colleagues tested subcutaneous ghrelin at 0.5 to 13 mcg/kg/day in cancer cachexia patients. Treated subjects gained 1 to 3 kg and increased caloric intake over 4 to 8 weeks [1]. A separate meta-analysis confirmed the appetite-stimulating effect across multiple populations (PMC3644599). The GHS-R1a target is so validated that anamorelin, a synthetic ghrelin receptor agonist, received approval in Japan for cancer cachexia and completed Phase 3 trials globally (eClinicalMedicine 2025). The practical problem is pharmacokinetic. Active acylated ghrelin survives 9 to 13 minutes in plasma after IV dosing. Even subcutaneous delivery extends this to only 30 to 60 minutes. No consumer peptide vendor stocks native ghrelin. Lab-grade material runs $253 or more per milligram from suppliers like Tocris and AnaSpec.
Ghrelin's biological activity starts at the GHS-R1a receptor, a G-protein-coupled receptor expressed in the anterior pituitary, arcuate nucleus, vagal afferents, and throughout the gastrointestinal tract. The receptor requires ghrelin's octanoyl modification at Ser3 for activation; des-acyl ghrelin does not bind. At the pituitary, GHS-R1a activates Gq/11-mediated signaling. Intracellular calcium rises. Growth hormone releases into circulation, independent of the GHRH pathway. Combined ghrelin plus GHRH stimulation testing produces larger GH peaks than either alone [3]. This is the basis for ghrelin-based GH diagnostics. The appetite arm runs through the hypothalamus. Ghrelin activates NPY/AgRP neurons in the arcuate nucleus while simultaneously inhibiting POMC/CART neurons. The net signal is hunger, peaking 30 to 60 minutes after administration. No other peripheral hormone does this; leptin, GLP-1, and PYY all suppress appetite. One detail separates ghrelin from every other peptide hormone. The GOAT enzyme attaches a medium-chain fatty acid (octanoyl, C8) to serine-3. Without this modification, the peptide cannot bind GHS-R1a. Des-acyl ghrelin circulates at 3 to 4 times the concentration of the active form but has zero receptor activity at the target. In the gut, ghrelin activates vagal afferents to speed gastric emptying and increase acid secretion. Peripheral tissues respond through AMPK-dependent signaling, shifting metabolism toward fatty acid oxidation and glucose sparing.
Native acylated ghrelin is effective for appetite stimulation and lean mass preservation in catabolic/wasting populations (cancer cachexia, COPD, heart failure) and reliably triggers GH pulses in clinical GH stimulation testing. All clinical dosing is weight-based (mcg/kg). Practical use is limited by extreme half-life instability (~9-13 min for active acyl-ghrelin IV). Ghrelin receptor agonists (anamorelin) have advanced to Phase 3 / Japan approval for cancer cachexia, underscoring validated therapeutic relevance of the GHS-R1a target.
Lundholm et al.: SC ghrelin 0.5-13 mcg/kg/day in cancer cachexia; PMID 18182992 (Neary et al. JCEM 2004). PMC3644599 appetite stimulation meta-analysis. Anamorelin Phase 3 gastric cancer RCT (eClinicalMedicine 2025).
Active acyl-ghrelin half-life only 9–13 min IV; no validated SC bioavailability measurement in humans. All clinical protocols are IV or weight-based SC: fixed-dose consumer-style tiers are not clinically derived. Native ghrelin is unavailable through consumer peptide channels. Cancer risk through GHS-R1a on tumor cell lines is clinically documented.
Native ghrelin has near-zero community self-administration. The research peptide community uses synthetic GHS-R1a agonists (GHRP-2, GHRP-6, ipamorelin, MK-677) exclusively. No consumer research peptide vendors stock native acylated ghrelin. Community familiarity is primarily informational: "hunger hormone" educational interest.
Science has extensive data (10,000+ PubMed papers, multiple Phase 2/3 trials); community does not use native ghrelin at all: synthetic GHS-R1a agonists serve the same receptor target with practical pharmacokinetics.
| Level | Dose / Injection | Frequency |
|---|---|---|
| Beginner | 50mcg | Daily |
| Moderate | 100mcg | 2x Daily |
| Aggressive | 200mcg | 2x Daily |
Native ghrelin is a lab chemical, not a consumer peptide. You won't find it at the usual research peptide vendors. The only real sources are laboratory suppliers like Tocris Bioscience or AnaSpec, and they charge $253+ per milligram. That price is telling you something about the practical reality of this compound. For the 5 mg vial at 2 mL bacteriostatic water: each 0.1 mL (10 units on an insulin syringe) delivers 250 mcg. A 50 mcg beginner dose is 2 units. A 100 mcg moderate dose is 4 units. The thing most people miss: acylated ghrelin is not the same as des-acyl ghrelin. The octanoyl group at Ser3 is what makes it active at GHS-R1a. Your certificate of analysis must specify which form you have. Temperature sensitivity is extreme; keep this frozen at -20C until reconstitution. After mixing, use within 2 weeks refrigerated. If you want GHS-R1a receptor effects with practical pharmacokinetics, GHRP-2 (100 mcg SC, 2 to 3 times daily), GHRP-6 (100 to 200 mcg SC before meals), or MK-677 (25 mg oral daily) are the community-tested alternatives. Dose on an empty stomach; food blunts the GH response.
Due to potential GHS-R1a desensitization with chronic exposure, cycling is recommended. Clinical research protocols typically use acute or short-term dosing. Monitor appetite, weight, and fasting glucose during on periods.
Chronic continuous GHS-R1a stimulation leads to receptor tachyphylaxis: reduced GH-releasing and appetite-stimulating response over time. Clinical cachexia protocols typically use 4–12 week defined courses rather than indefinite continuous use. A 4-week off-break allows receptor resensitization. No published cycling data exists specifically for native ghrelin; recommendation is extrapolated from GHRP class receptor pharmacology and the 8/4 cycling pattern used in community GHS-R agonist protocols.
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Expected: 1–3 kg body weight gain in cachectic populations over 4–8 weeks; improved appetite and food intake; IGF-1 elevation; potential improvement in lean body mass.
Monitor: Fasting blood glucose before and weekly during treatment. Body weight and food intake log. IGF-1 at 4 weeks if prolonged course.
Allow it to reach refrigerator temperature (2 to 8C) before reconstitution. Do not leave at room temperature.
Direct the stream along the inside wall of the vial. Swirl gently until dissolved. Do not shake.
Concentration after reconstitution: 5 mg in 2 mL = 2,500 mcg per mL. Each unit on a U-100 insulin syringe (0.01 mL) = 25 mcg.
For 100 mcg (moderate): 4 units. For 200 mcg (aggressive): 8 units. Clinical weight-based dosing at 1 mcg/kg for a 70 kg person is 70 mcg, which is approximately 2.8 units.
Pinch skin at the abdomen or thigh. Insert a 29 to 31 gauge needle at a 45-degree angle subcutaneously. Inject slowly. Hold 5 seconds before withdrawing.
Rotate injection sites with each administration.
Timing: for appetite stimulation, inject 30 to 60 minutes before the main meal. For GH release, inject on an empty stomach (minimum 2 hours fasted, 4 hours preferred), ideally morning or before sleep.
Use within 2 weeks. For best acyl-ghrelin retention, use within 24 hours of mixing.
1–5 mcg/kg single bolus for GH stimulation testing
Gold standard for GH stimulation tests and PK studies. Fastest onset (GH peak 15–30 min). Acyl-ghrelin t½ ~9–13 min IV. Requires IV access and clinical monitoring. Not suitable for self-administration.
Rate-controlled to maintain target ghrelin plasma levels; varies by study protocol
Used in PK characterization and metabolic studies. Sustains active ghrelin levels but requires hospital setting. Rebounding GH/insulin/glucagon after infusion cessation is a known clinical concern.
0.5–13 mcg/kg/day SC for cachexia; ~1 mcg/kg for appetite studies
Active ghrelin peak at ~30 min SC. SC bioavailability not formally measured in humans: estimated but unconfirmed. Most practical route outside IV setting. Rapid des-acylation by plasma esterases reduces active fraction significantly.
N/A: peptide degraded by GI proteases and nasal mucosal enzymes
Oral route not viable for native ghrelin. Non-peptide GHS-R1a agonist MK-677 (ibutamoren) was developed specifically to achieve oral bioavailability of ghrelin receptor activation.
Synthetic GHS-R1a agonist that mimics ghrelin's GH-releasing effects with practical pharmacokinetics (t½ ~1h). Community-preferred alternative to native ghrelin for GH release.
100 mcg SC 2–3x daily on empty stomach
Synthetic GHS-R1a agonist; similar mechanism to native ghrelin with stronger appetite drive than GHRP-2. Preclinical and community evidence for GH/appetite effects.
100–200 mcg SC 2–3x daily before meals
Selective GHRP with minimal cortisol/prolactin stimulation compared to native ghrelin. Often paired with CJC-1295 for GH optimization in community protocols.
Oral non-peptide GHS-R1a agonist: the most practical route to sustained ghrelin receptor activation. Eliminates injection issues and half-life degradation problems of native ghrelin.
25 mg oral daily before bed
Directly opposes ghrelin-mediated GH release at the pituitary. Somatostatin analogs (octreotide, lanreotide) are functional antagonists: co-administration eliminates ghrelin's GH-releasing effect entirely.
Do not combineOpposing appetite effects: GLP-1RAs suppress hunger while ghrelin stimulates it. Co-administration creates pharmacological conflict and negates ghrelin's orexigenic indication.
Ghrelin raises blood glucose via GH-mediated insulin resistance and direct hepatic effects. Dose adjustment of diabetes medications required if co-administered; increased monitoring mandatory.
Both ghrelin and glucocorticoids raise blood glucose via separate mechanisms: additive hyperglycemia risk is clinically documented.
The most serious safety concern with ghrelin is the cancer risk. GHS-R1a and GHS-R1b receptors are expressed on multiple cancer cell lines. Acylated ghrelin activates PI3K/Akt proliferative signaling and has been shown to induce cisplatin resistance in some tumor models. Any active or suspected malignancy is a hard contraindication. The irony is that cancer cachexia is ghrelin's primary therapeutic indication. That creates genuine clinical tension requiring oncologist involvement for any use. Blood glucose elevation is the second major concern. Ghrelin raises glucose through two mechanisms: GH-mediated insulin resistance and direct hepatic glucose output. Clinical trial participants required weekly fasting glucose monitoring. If fasting glucose exceeds 126 mg/dL without pre-existing diabetes, discontinuation is the recommended response. Pre-diabetic individuals and anyone on insulin or oral hypoglycemics need dose adjustments and closer monitoring. Corticosteroid co-administration compounds this risk through separate hyperglycemic pathways. Appetite stimulation itself is a safety issue in specific populations. Prader-Willi syndrome patients already have pathologically raised endogenous ghrelin driving extreme hyperphagia. Researchers are actually working on GOAT inhibitors to block ghrelin's effects in PWS. Active eating disorders (binge eating disorder, bulimia) are absolute contraindications. Common side effects from clinical trials include increased hunger (expected and dose-dependent), transient flushing within the first 30 minutes, mild nausea, and diarrhea. Raised gastric acid secretion has been reported. Water retention and mild edema appeared in some study participants, related to sustained IGF-1 elevation from repeated GH pulses. Injection site reactions (redness, swelling) occur with subcutaneous administration, consistent with other injectable peptides. No safety data exists for ghrelin use during pregnancy or breastfeeding. This is an absolute contraindication. The pharmacokinetic profile creates its own practical safety issue. Active acylated ghrelin degrades in 9 to 13 minutes IV, roughly 30 minutes subcutaneously. Temperature excursions during storage destroy bioactivity. Material from non-laboratory suppliers should be treated as unverifiable. Lab-grade product from suppliers like Tocris or AnaSpec requires validated cold-chain handling at $253+ per milligram. Drug interactions need specific attention. Insulin and oral hypoglycemics may need dose adjustment. Somatostatin analogs (octreotide, lanreotide) directly block ghrelin's GH-releasing effect. GLP-1 receptor agonists (semaglutide, liraglutide) create pharmacological conflict by suppressing the appetite ghrelin is trying to stimulate. Exogenous growth hormone adds to IGF-1 elevation risk. Corticosteroids compound the hyperglycemia problem. When to stop: fasting glucose above 180 mg/dL unresponsive to management, any new cancer diagnosis, weight gain goal reached, or beyond 12 weeks of continuous use (long-term safety data past this point is limited). When to see a doctor: persistent hyperglycemia, signs of new mass or unexplained weight changes, or any allergic reaction at the injection site.
Verify Ghrelin dosing and safety with a second opinion
Native acylated ghrelin is not available from consumer research peptide vendors. It is sold exclusively through laboratory chemical suppliers (Tocris Bioscience, AnaSpec, Novo Pro Labs) at research-grade pricing ($253+/mg) for in vitro / animal research. The critical acylation at Ser3 (octanoyl group) required for bioactivity is chemically fragile and temperature-sensitive: even properly sourced material requires validated cold-chain handling. There is no consumer-facing quality standard or certificate of analysis framework applicable here. Anyone receiving ghrelin from a non-laboratory supplier should be treated as extremely high-risk.
| Test | When | Target |
|---|---|---|
| Fasting blood glucose | Baseline, then weekly during active dosing | <100 mg/dL fasting; >126 mg/dL warrants dose reduction or discontinuation |
| IGF-1 | Baseline, then at 4 weeks for courses ≥4 weeks | Age/sex-adjusted reference; avoid supraphysiologic elevation |
| Body weight and food intake log | Daily during active protocol | — |
| HbA1c | Baseline and at 8–12 weeks for extended courses or in pre-diabetic individuals | <5.7%; higher risk monitoring threshold at ≥6.0% |
Ghrelin raises blood glucose via GH-mediated insulin resistance and direct hepatic glucose output; clinically documented in trial populations
Sustained GH stimulation elevates IGF-1; relevant for dose safety and efficacy confirmation
Primary efficacy endpoint in cachexia indication; tracks appetite response and weight trajectory
Chronic GH elevation induces long-term insulin resistance accumulation
Rapid increase in circulating GH levels within 15-30 minutes. Noticeable hunger and appetite stimulation within 30-60 minutes. Possible mild flushing. Effects wane within 2-3 hours due to short half-life.
Consistent appetite increase when dosed pre-meal. GH pulses become more predictable. Some users report improved sleep quality. Possible mild water retention and increased food intake.
Measurable increase in caloric intake and body weight in cachectic populations. Improved gastric emptying rates. IGF-1 levels may begin to rise. Fat-free mass may start improving in catabolic patients.
Clinical studies show meaningful weight gain in cachexia patients (1-3 kg). Sustained GH elevation with continued dosing. Body composition shifts toward lean mass preservation. Some GHS-R1a tachyphylaxis may begin to appear.
Receptor desensitization may reduce GH-releasing efficacy. Cycling off for 4 weeks is recommended to restore sensitivity. Appetite effects may partially persist. Long-term safety data beyond 12 weeks is limited.
First dose (0 to 2 hours): GH spikes within 15 to 30 minutes. Hunger hits at the 30 to 60 minute mark. You might notice mild flushing. Active ghrelin clears plasma fast, 9 to 13 minutes IV, roughly 30 minutes subcutaneously. Effects taper within 2 to 3 hours. No community self-administration data exists for native ghrelin; GHRP-2 users report comparable hunger onset at 20 to 30 minutes through the same receptor. Days 1 to 7: Appetite increases become consistent when dosing before meals. GH pulses settle into a predictable pattern. Some mild water retention and bloating are common. IGF-1 starts climbing with daily dosing. Check fasting glucose at day 7. Weeks 2 to 4: Cachectic populations show measurable caloric intake increases. Gastric emptying rates improve (the gastroprokinetic effect). IGF-1 levels are clearly rising. Fat-free mass may begin recovering in patients with active wasting. Pre-diabetic individuals should be watching fasting glucose closely here. Weeks 4 to 8: The cachexia trial data landed on 1 to 3 kg of weight gain by this point. GH elevation holds steady. Body composition shifts toward lean mass preservation over fat gain. Some GHS-R1a tachyphylaxis may appear; the appetite effect tends to persist more than the GH response. Weeks 8 and beyond: Receptor desensitization is expected with continuous use past 8 weeks. GH-releasing efficacy drops more than appetite effects. Glucose intolerance may accumulate progressively. A 4-week off-period is the standard recommendation to restore sensitivity. Long-term safety data beyond 12 weeks is limited across all published protocols.
GH peaks within 15–30 min of IV or SC administration. Active ghrelin (acyl form) clears plasma in 9–13 min IV / ~30 min SC. Appetite stimulation onset within 30–60 min. Transient mild flushing possible.
Not applicable: native ghrelin not community-used. GHRP-2 (equivalent receptor effect): users report hunger surge within 20–30 min, mild flushing, occasional warmth.
Consistent appetite increase when dosed pre-meal. GH pulses reproducible. Mild water retention possible. IGF-1 begins to rise with daily dosing.
N/A (see GHRP-2/GHRP-6 for community-equivalent timeline)
Measurable increase in caloric intake and body weight in cachectic populations. Improved gastric emptying (gastroprokinetic effect). IGF-1 levels rising. Fat-free mass beginning to improve.
N/A
Clinical cachexia trials: 1–3 kg weight gain. Sustained GH elevation. Body composition shifts toward lean mass preservation. Some GHS-R1a tachyphylaxis may emerge.
N/A
GHS-R1a tachyphylaxis expected with continuous daily use beyond 8 weeks. Efficacy reduction for GH-releasing endpoint more pronounced than for appetite endpoint. Glucose intolerance may accumulate.
N/A
Source: Acyl-ghrelin plasma t1/2 9-13 min (PMID 15080773); SC half-life estimated at 60-90 min based on acyl-ghrelin clearance kinetics
Loading the interactive decay curve.
Ghrelin has no FDA approval for any therapeutic indication. Its regulatory status is research-only. No consumer-facing peptide vendor stocks native acylated ghrelin. The compound is available exclusively from laboratory chemical suppliers (Tocris Bioscience, AnaSpec, Novo Pro Labs) for in vitro and animal research purposes. Anamorelin, a synthetic oral ghrelin receptor agonist, received approval in Japan for cancer cachexia in 2021. No equivalent approval exists in the United States or European Union for native ghrelin or any oral GHS-R1a agonist. WADA prohibits all growth hormone secretagogues under section S2 of the prohibited list. This includes native ghrelin and synthetic GHS-R1a agonists (GHRP-2, GHRP-6, MK-677). Athletes subject to anti-doping testing should be aware that ghrelin and its metabolites are detectable. This content is for educational and research purposes only. It does not constitute medical advice. Consult a qualified healthcare provider before using any research compound. Ghrelin use outside of approved clinical research protocols is at the individual's own risk.
Peptide Schedule Research TeamReviewed Apr 20268 Citations
