Evidence standard: Claims graded by study type. Human RCT data cited by author or trial. Speculative claims labelled.
Regulatory note: GHRP-2 is not FDA-approved. All dose figures reflect published research and investigational use, not therapeutic guidance.
Key Takeaways
- The most-studied single injection dose is 100 mcg subcutaneously, derived from 1 mcg/kg body weight in typical adult subjects and used as the standard GH stimulation test dose in multiple published human studies.
- Doses above roughly 300 mcg per injection show diminishing returns on GH release and increase cortisol and prolactin co-secretion, a pattern documented in human pharmacology studies including work by Arvat et al.
- A 5mg vial reconstituted with 2.5 mL bacteriostatic water yields 2,000 mcg/mL; a 10mg vial with 5 mL gives the same concentration, making 100 mcg equal to exactly 0.05 mL on a U-100 syringe either way.
- GHRP-2 reliably co-stimulates cortisol and prolactin alongside GH, unlike ipamorelin, a distinction most dosage pages omit entirely.
- Fasting for at least 90 minutes before injection is consistently required in human GHRP-2 study protocols because postprandial somatostatin tone measurably blunts GH pulse amplitude.
Direct Answer: What Is the Standard GHRP-2 Dosage?
The most evidence-backed GHRP-2 dosage is 100 mcg per injection, 2 to 3 times per day, for a daily total of 200 to 300 mcg. This reflects the dose used in human GH stimulation studies. Doses beyond 300 mcg per injection do not proportionally increase GH release and raise off-target hormone effects. No FDA-approved dosing regimen exists.
Table of Contents
- Evidence Ledger: What Do We Actually Know?
- How GHRP-2 Triggers GH Release (With Specific Numbers)
- Dosage Table by Goal and Body Weight
- Vial Math: 5mg and 10mg Reconstitution
- Timing and Fasting: The Chemistry Behind the Rule
- What Most GHRP-2 Dosage Pages Get Wrong
- Honest Head-to-Head: GHRP-2 vs. Ipamorelin vs. GHRP-6
- Label and COA Literacy: Reading a GHRP-2 Product
- Side Effects That Are Dose-Dependent
- FAQ
- Sources
What Do We Actually Know? The Evidence Ledger
| Claim | Best Evidence Type | Effect Direction | Confidence |
|---|---|---|---|
| Single IV or SC dose of ~1 mcg/kg raises GH acutely in healthy adults | Human RCT / crossover studies (Arvat et al., Ghigo et al., multiple groups) | Consistent GH increase | High |
| GH response plateaus or diminishes above ~300 mcg per injection | Human dose-response studies | Non-linear ceiling effect | Moderate |
| GHRP-2 co-stimulates cortisol and prolactin at clinical doses | Human controlled studies (Arvat et al. 1997, Ghigo group) | Consistent elevation | High |
| GHRH co-administration produces synergistic GH release | Human crossover studies | Greater GH pulse vs. either alone | High |
| Repeated daily dosing improves body composition over weeks | Animal studies; very limited human data at research doses | Positive in animals, unclear in humans | Low |
| Fasting preserves GH pulse amplitude post-injection | Human pharmacology studies (protocol requirement across labs) | Fasting increases peak GH | Moderate |
| Optimal dosing frequency of 3x/day for IGF-1 elevation | Extrapolated from half-life data and animal studies | Plausible but unconfirmed in long-term human RCT | Very Low |
How GHRP-2 Triggers GH Release (With Specific Numbers)
GHRP-2 (pralmorelin; sequence Ala-D-2Nal-Ala-Trp-D-Phe-Lys-NH2) is a synthetic hexapeptide that acts as a full agonist at the growth hormone secretagogue receptor type 1a (GHS-R1a), also called the ghrelin receptor. GHS-R1a is expressed on pituitary somatotroph cells and in the hypothalamus.
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Try the BMI Calculator →Binding GHS-R1a triggers a Gq/11-coupled phospholipase C pathway, raising intracellular calcium in somatotrophs and directly driving GH granule exocytosis. Simultaneously, GHRP-2 acts at the hypothalamic level to suppress somatostatin release, removing the brake on GH secretion. These two actions are why GHRP-2 produces a larger GH pulse than simple somatostatin withdrawal alone.
Plasma half-life: GHRP-2 has a short plasma half-life estimated at roughly 15 to 30 minutes in human pharmacokinetic observations, which explains why dosing more than once daily is needed to generate multiple GH pulses and why a single morning dose is insufficient for sustained elevation of GH pulsatility across 24 hours.
What this mechanism does NOT prove: A measurable GH pulse does not automatically translate to meaningful downstream IGF-1 elevation, improved lean mass, or fat loss in healthy adults over a research course. GH pulses are physiologically normal many times daily; adding pharmacological pulses on top of intact pulsatile GH secretion may produce proportionally smaller incremental benefit than in GH-deficient patients, where most clinical GH literature is based.
Dosage Table by Body Weight and Common Research Protocols
| Body Weight | 1 mcg/kg Dose | 2 mcg/kg Dose | Common Protocol Total/Day | Note |
|---|---|---|---|---|
| 60 kg (132 lb) | 60 mcg | 120 mcg | 180 to 240 mcg (3 injections) | Use lower end; hunger effect significant |
| 75 kg (165 lb) | 75 mcg | 150 mcg | 225 to 300 mcg (3 injections) | 100 mcg flat dose also commonly used |
| 90 kg (198 lb) | 90 mcg | 180 mcg | 270 to 300 mcg (3 injections) | Ceiling effect begins near 300 mcg/injection |
| 100+ kg (220+ lb) | 100 mcg | 200 mcg | 300 mcg max recommended per injection | No evidence supports exceeding 300 mcg/injection |
Vial Math: How to Reconstitute GHRP-2 5mg and 10mg Vials
Peptide vials contain lyophilized powder measured in milligrams. To get an injectable solution you add bacteriostatic water (BW). The goal is a concentration that lets you draw a practical, accurate volume on a standard U-100 insulin syringe (where 1 unit = 0.01 mL).
| Vial Size | BW to Add | Resulting Concentration | Volume for 100 mcg | Units on U-100 Syringe |
|---|---|---|---|---|
| 5mg (5,000 mcg) | 2.5 mL | 2,000 mcg/mL (2 mg/mL) | 0.05 mL | 5 units |
| 5mg (5,000 mcg) | 5.0 mL | 1,000 mcg/mL (1 mg/mL) | 0.10 mL | 10 units |
| 10mg (10,000 mcg) | 5.0 mL | 2,000 mcg/mL (2 mg/mL) | 0.05 mL | 5 units |
| 10mg (10,000 mcg) | 10.0 mL | 1,000 mcg/mL (1 mg/mL) | 0.10 mL | 10 units |
Reconstitution technique: Angle the needle against the glass wall and let the water run down the side slowly; do not jet liquid directly onto the powder cake, as this can cause mechanical degradation of fragile peptide bonds. Swirl gently, do not vortex. Inspect for cloudiness or particulates before each draw; discard if present.
Always cross-check the COA. A vial labelled "10mg" from a research supplier may have an actual peptide content verified by HPLC of, say, 9.2mg or 10.6mg. Use the COA-confirmed mass in your concentration calculation, not the label alone.
Timing and Fasting: The Chemistry Behind the Rule
Every published GHRP-2 human study that aimed to measure GH response required subjects to be fasted. This is not arbitrary.
After a carbohydrate or mixed meal, blood glucose rises, which triggers hypothalamic somatostatin release. Somatostatin binds SSTR2 and SSTR5 on pituitary somatotrophs and directly inhibits both GH secretion and GHS-R1a signaling through Gi-coupled pathways. In plain terms, a fed state primes a hormonal brake that partially blocks GHRP-2's mechanism of action at the pituitary level.
The practical implication: injecting GHRP-2 after a carbohydrate-rich meal does not simply lower the GH response a little; it can substantially blunt the pulse. Research convention of 90-minute pre-injection fasting is a minimum, not a preference. A 30-minute post-injection fast is also standard to protect the tail end of the GH pulse from the same somatostatin surge that follows eating.
Moderate protein intake does not raise somatostatin as sharply as carbohydrates or fat, but most protocols still require full fasting to keep conditions standardized and to maximize pulse amplitude.
What Most GHRP-2 Dosage Pages Get Wrong
1. They ignore the cortisol and prolactin co-secretion. GHRP-2 is not selective for GH. Multiple human studies including Arvat et al. (1997, published in the Journal of Clinical Endocrinology and Metabolism) documented that GHRP-2 reliably elevates ACTH, cortisol, and prolactin alongside GH in healthy volunteers. This is not a rare side effect; it is a pharmacological property of GHS-R1a agonism outside the pituitary somatotrophs. Pages that list only "water retention and hunger" as side effects are omitting a clinically meaningful effect.
2. They treat lyophilized stability as equivalent to reconstituted stability. Dry GHRP-2 powder stored at reasonable temperatures is relatively stable. Once reconstituted in bacteriostatic water, the peptide is in aqueous solution where hydrolysis of peptide bonds proceeds continuously. The rate accelerates with heat, light, and repeated freeze-thaw cycles. There are no published peer-reviewed stability kinetics for this specific peptide in BW at refrigerator temperatures, so any page giving you an exact "good for 30 days" number is either extrapolating from other peptides or fabricating precision. Reasonable convention from compounding pharmacy practice is use within a few weeks and refrigerate consistently, but that is convention, not peer-reviewed kinetic data for GHRP-2 specifically.
3. They quote a fixed dose without noting the ceiling effect. GHRP-2's GH-releasing effect is not linear with dose. Human dose-response data show a plateau, and exceeding roughly 300 mcg per injection adds mostly cortisol and hunger, not proportionally more GH. A blanket recommendation of "100 to 300 mcg" without explaining where the ceiling is leaves readers to assume bigger is better.
4. They omit purity risk. Research-grade GHRP-2 from unregulated suppliers is not pharmaceutical-grade. HPLC purity of 98% is claimed routinely; independent testing by organizations that have analyzed research peptides has repeatedly found products in this category with lower purity, incorrect concentrations, or contamination. This is a real sourcing risk, not a theoretical one.
Honest Head-to-Head: GHRP-2 vs. Ipamorelin vs. GHRP-6
| Property | GHRP-2 | Ipamorelin | GHRP-6 |
|---|---|---|---|
| GH release potency (relative) | High | Moderate to high | Moderate |
| Cortisol / ACTH elevation | Yes, consistently at clinical doses | Minimal, most selective GHS-R agonist studied | Yes, moderate |
| Prolactin elevation | Yes | Minimal | Moderate |
| Hunger / appetite stimulation | Moderate to strong | Low | Strong (more than GHRP-2) |
| Human RCT data available | Yes (multiple GH stimulation studies) | Limited; animal data stronger | Yes (GH stimulation studies) |
| Where GHRP-2 loses | Off-target hormone effects vs. ipamorelin; less selective | N/A | N/A |
| Regulatory status (US) | Not FDA-approved; research chemical | Not FDA-approved; research chemical | Not FDA-approved; research chemical |
Bottom line: If cortisol co-elevation is a concern (stress recovery, adrenal context, HPA axis sensitivity), ipamorelin's selectivity profile is a meaningful advantage over GHRP-2. If raw GH pulse amplitude alongside a GHRH analog is the goal and cortisol effects are acceptable, GHRP-2 is among the more potent options studied in humans. GHRP-2 concedes selectivity to ipamorelin; that is a real trade-off, not marketing.
Label and COA Literacy: Reading a GHRP-2 Product
Before calculating any dose, assess the product itself using these checkpoints:
| What to Look For | What It Tells You | Red Flag |
|---|---|---|
| HPLC purity percentage | Fraction of material that is actually GHRP-2 | Below 98%; no HPLC data at all |
| Mass spectrometry confirmation | Correct molecular identity (MW 817.97 g/mol for GHRP-2) | No MS data; only "certificate" with no method stated |
| Peptide content by weight | Actual mcg in the vial to use in reconstitution math | Label mass with no analytical verification |
| Sterility / endotoxin testing | Safety for subcutaneous injection | No LAL endotoxin result on COA |
| Lot number on COA matches vial | COA is for this specific batch | Generic undated COA with no lot number |
A degraded or impure product looks identical to a good one in solution. Cloudiness, particulates, or an unusual color after reconstitution are discard signals, but a clear solution is not proof of purity; only analytical testing is.
Side Effects That Are Dose-Dependent
These effects are drawn from published human pharmacology studies and investigational reports, not FDA-reviewed drug labeling:
- Hunger: The most consistent dose-dependent effect. GHS-R1a agonism in the hypothalamus drives appetite signaling via ghrelin-mimicry pathways. More pronounced at doses above 100 mcg. GHRP-6 causes stronger hunger; ipamorelin causes significantly less.
- Cortisol and ACTH elevation: Documented in human studies at 1 to 2 mcg/kg doses. Magnitude is dose-related and is additive over multiple daily injections. Chronic cortisol elevation carries its own metabolic risks.
- Prolactin elevation: Seen in human studies, mechanism is GHS-R1a-mediated at the pituitary lactotroph level. Clinical significance at research doses in otherwise healthy adults is not well characterized.
- Water retention: Common at initiation; likely GH-mediated via renal effects on sodium handling. Tends to reduce over time.
- Injection site reactions: Expected with any subcutaneous peptide injection; rotate sites.
- Transient hypoglycemia: Reported rarely; GH itself can transiently lower blood glucose in the acute post-injection window before GH's insulin-antagonizing effects dominate.
Frequently Asked Questions
What is the standard GHRP-2 dosage per injection?
Research protocols most commonly use 100 mcg per injection subcutaneously. Clinical GH stimulation tests have used doses from 1 mcg/kg up to 2 mcg/kg body weight. Doses above 300 mcg per injection do not proportionally increase GH release and add side-effect burden.
How many times per day should GHRP-2 be dosed?
Research protocols typically use 2 to 3 injections per day. More frequent dosing takes advantage of GHRP-2's short half-life (roughly 15 to 30 minutes in plasma) and allows each pulse to land during a natural GH trough, maximizing each pituitary response.
What is the GHRP-2 dosage per day in total?
A commonly studied daily total is 200 to 300 mcg, split across 2 to 3 injections. This is not an FDA-approved therapeutic dose; it reflects typical research and investigational use patterns observed in published peptide literature.
How do I reconstitute a GHRP-2 5mg vial?
Adding 2.5 mL of bacteriostatic water to a 5mg vial yields 2 mg per mL (2,000 mcg/mL). Drawing 0.05 mL (5 units on a U-100 syringe) delivers 100 mcg. Always confirm your vial's exact peptide content on the certificate of analysis before calculating.
How do I use a GHRP-2 10mg vial?
Adding 5 mL of bacteriostatic water to a 10mg vial also yields 2 mg per mL (2,000 mcg/mL), keeping the math identical. A 0.05 mL draw on a U-100 insulin syringe delivers 100 mcg. Refrigerate after reconstitution and discard per your supplier's stated expiry window.
Should GHRP-2 be taken on an empty stomach?
Yes. Somatostatin tone rises after carbohydrate or fat intake, which blunts the pituitary GH response to GHRP-2. Research protocols typically require at least 90 minutes of fasting before injection and 30 minutes afterward to protect the GH pulse amplitude.
Is GHRP-2 more effective combined with a GHRH like CJC-1295?
Human studies show that combining a GHRH analog with GHRP-2 produces a synergistic GH release greater than either alone. The two peptides act on different receptor classes (GHRH-R and GHS-R1a), and when used together the GH peak can be several-fold higher than with GHRP-2 alone.
What side effects are associated with GHRP-2 dosing?
Reported effects include increased hunger (via ghrelin receptor agonism), transient water retention, elevated cortisol and prolactin at higher doses, and injection-site reactions. Hunger is the most consistent and dose-related effect. These are research observations, not FDA-reviewed safety data.
Does GHRP-2 cause a cortisol or prolactin spike?
Yes. Published human studies show GHRP-2 raises both cortisol and prolactin alongside GH, particularly at doses at or above 1 mcg/kg. This effect is GHS-R1a-mediated and is more pronounced with GHRP-2 than with ipamorelin, which is considered more selective.
How should reconstituted GHRP-2 be stored?
Reconstituted GHRP-2 should be refrigerated at 2 to 8 degrees Celsius and protected from light. Lyophilized (dry) powder is more stable and can typically be stored at room temperature short-term, but reconstituted solution degrades faster due to hydrolysis of peptide bonds in aqueous solution.
Is GHRP-2 legal to buy and use?
GHRP-2 is not FDA-approved as a drug. In the United States it is classified as a research chemical and is not legal for human use outside of clinical trials. It is also prohibited by WADA in competitive sport. Regulatory status varies by country; always verify local rules before acquiring.
How long does it take to see results from GHRP-2?
GHRP-2 produces a measurable GH pulse within 15 to 60 minutes of injection in human studies. Downstream outcomes like changes in body composition or recovery take weeks to months of consistent administration and have limited controlled human trial data at research doses.
Sources
- Arvat E, et al. "Preliminary evidence that Ghrelin, the natural GH secretagogue (GHS)-receptor ligand, strongly stimulates GH secretion in humans." Journal of Endocrinological Investigation. 2000; 23(8):493-5. (GHRP-2 comparator context.)
- Arvat E, et al. "GHRP-2 stimulates GH, ACTH, cortisol, and prolactin secretion in humans." Journal of Clinical Endocrinology and Metabolism. 1997. (Foundational human cortisol/prolactin co-secretion data.)
- Ghigo E, et al. "New approach to the diagnosis of growth hormone deficiency in adults." European Journal of Endocrinology. 1996;134(3):352-6. (GHRP-2 as GH stimulation test agent.)
- Bowers CY. "Growth hormone-releasing peptide (GHRP)." Cellular and Molecular Life Sciences. 1998;54(12):1316-29. (Mechanism and dose-response review.)
- Petersenn S, et al. "Structure and regulation of the human ghrelin receptor gene." Endocrinology. 2001;142(6):2649-59. (GHS-R1a receptor biology.)
- Kojima M, et al. "Ghrelin is a growth-hormone-releasing acylated peptide from stomach." Nature. 1999;402:656-660. (Endogenous ligand for GHS-R1a, mechanistic foundation.)
- World Anti-Doping Agency (WADA). Prohibited List 2026. https://www.wada-ama.org/en/prohibited-list. (GHRP-2 prohibition classification.)
- US FDA. "Compounded Drug Products That Are Essentially Copies of Approved Drug Products." FDA Guidance 2018. (Regulatory context for compounded peptides.)
- United States Pharmacopeia (USP). General Chapter 797: Pharmaceutical Compounding - Sterile Preparations. (Bacteriostatic water reconstitution and sterility standards.)