GHRP-2 vs GHRP-6 (Growth Hormone Releasing Peptide-6)
A ghrelin-receptor agonist that triggers a growth hormone pulse from the pituitary. Approved in Japan — but only as a single 100 μg intravenous dose for DIAGNOSING growth hormone deficiency, not as a treatment [6]. The one chronic human study, 8 months in 6 children, raised GH but left IGF-I unchanged [5].
A synthetic hexapeptide that signals your pituitary to release growth hormone through a unique pathway, with emerging evidence of heart-protective benefits.
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Quick comparison
Dose range
GHRP-2
100–100 mcg
GHRP-6 (Growth Hormone Releasing Peptide-6)
100–100 mcg
Frequency
GHRP-2
Single dose (approved diagnostic use)
GHRP-6 (Growth Hormone Releasing Peptide-6)
Multiple times daily
Administration
GHRP-2
Intravenous (approved diagnostic use)
GHRP-6 (Growth Hormone Releasing Peptide-6)
Subcutaneous injection
Cycle length
GHRP-2
Not established — the approved use is one injection
GHRP-6 (Growth Hormone Releasing Peptide-6)
8-12 weeks
Onset speed
GHRP-2
Rapid (hours to days)
GHRP-6 (Growth Hormone Releasing Peptide-6)
Moderate (1-2 weeks)
Evidence level
GHRP-2
Approved diagnostic agent in Japan; no treatment approval anywhere
GHRP-6 (Growth Hormone Releasing Peptide-6)
Limited human trials
Benefit ratings
GH Release
Recovery Speed
Sleep Quality
Muscle Recovery and Growth
Cellular Health and Protection
Appetite and Nutrient Intake
Compound specifications
GHRP-2
Molecular formula
C45H55N9O6
Molecular weight
817.97 g/mol
Half-life
15-60 minutes
Bioavailability
High (subcutaneous)
CAS number
158861-67-7
GHRP-6 (Growth Hormone Releasing Peptide-6)
Molecular formula
C46H56N12O6
Molecular weight
873.0 g/mol
Half-life
~2.5 hours
Bioavailability
<1% oral, high subcutaneous
CAS number
87616-84-0
Dosing compared
GHRP-2
Intravenous
100 mcg
Single dose, once — this is a diagnostic test · One administration
The only dose of GHRP-2 approved by any regulator. Japan approves pralmorelin hydrochloride as GHRP Kaken 100 for diagnosing growth hormone deficiency: dissolve the vial in 10 mL of saline immediately before use and inject 100 μg slowly into a vein, fasted, for anyone 18 or over. Children aged 4 to under 18 get 2 μg/kg, capped at 100 μg above 50 kg. Blood is then sampled to see how much growth hormone the pituitary releases [6]. It is a one-off test. Nothing about this approval extends to repeated dosing or to injecting under the skin.
Subcutaneous
0.3 – 3 mcg/kg/day
Once daily · 2 months per dose level, 8 months in total
The only chronic subcutaneous dosing ever published, and it was in 6 growth-hormone-deficient children, not adults: 0.3, then 1.0, then 3.0 mcg/kg per day, each for 2 months [5]. Overnight GH rose with dose and growth velocity improved, but serum IGF-I and IGFBP-3 did not increase at any dose, and each injection's effect was brief. For a 75 kg adult these levels would be about 22 to 225 mcg a day — which is where the commonly quoted per-dose figures roughly land, though no trial has given them to an adult on that schedule.
100 – 300 mcg per dose
1-3 times daily (community practice) · Undefined — no trial has run this schedule
Community-reported, not peer-reviewed and not on any label. This is the schedule most people asking about GHRP-2 mean, and it is worth being plain about what stands behind it: no human trial has dosed an adult subcutaneously one to three times daily at these amounts. The previous version of this page attributed the range to a study that does not contain it. What IS known at comparable exposures is that GHRP-2 raises food intake substantially — 33.5% above placebo at 1 mcg/kg/hour in 19 adults [7] — and that in the one chronic study IGF-I did not move [5].
GHRP-6 (Growth Hormone Releasing Peptide-6)
Subcutaneous
~100 mcg per injection (approx. 1 mcg/kg)
1-3 times daily, on an empty stomach · Open-ended in research practice
Research-practice GH-secretagogue dosing; the ~100 mcg anchor reflects the validated 1 mcg/kg GH-saturating dose, though no isolated subcutaneous human dose-response trial exists [6].
Intravenous
1 mcg/kg bolus (optionally followed by 1 mcg/kg/hr infusion)
Single bolus for acute GH testing; infusion studies ran up to ~34 hours · Acute test or infusion study
Trial-established near-maximal GH-releasing intravenous dose in healthy men; pituitary responsiveness maintained over prolonged infusion [6]. Dose-response in men: mean peak GH of 7.6, 16.5, and 68.7 µg/L at 0.1, 0.3, and 1.0 µg/kg respectively [7].
Best suited for
GHRP-2
Natural Growth Hormone Optimization
GHRP-2 excels at stimulating your pituitary to release more of your own growth hormone. Unlike synthetic HGH, it works with your body's natural feedback systems, creating more physiological GH pulses that mimic what your body did when you were younger.
Recovery and Muscle Building
Athletes and fitness enthusiasts love GHRP-2 for its ability to speed up recovery between workouts. The elevated GH and IGF-1 levels help repair muscle tissue faster, reduce soreness, and support lean muscle growth—especially when combined with proper training and nutrition.
Deep Sleep Enhancement
One of the most noticeable effects users report is dramatically improved sleep quality. GHRP-2 taken before bed can enhance deep sleep phases, which is when your body does most of its repair work. Many users report waking up feeling more refreshed and recovered.
Anti-Aging and Vitality
As we age, natural GH production declines significantly. GHRP-2 helps restore more youthful GH levels, which can translate to better skin elasticity, improved energy, enhanced recovery capacity, and that overall feeling of vitality that tends to fade with age.
Appetite Stimulation
Unlike many peptides that suppress appetite, GHRP-2 is known for increasing hunger. This makes it ideal for hard-gainers trying to build muscle or anyone who struggles to eat enough calories. The appetite boost typically kicks in within 20-30 minutes of injection.
GHRP-6 (Growth Hormone Releasing Peptide-6)
Athletes and Serious Trainers
If you're hitting the gym hard and want better recovery and muscle growth, GHRP-6 amplifies your body's natural GH response. This is particularly valuable during intense training phases when you want to maximize adaptation and minimize soreness. The appetite stimulation also helps you consume the calories you need to grow.
Those Exploring Novel Peptide Protocols
GHRP-6 offers a unique mechanism through the ghrelin receptor, making it valuable for users who want to explore diverse GH-stimulation pathways. It works distinctly from GHRH-based approaches and pairs well with other GH secretagogues for synergistic effects.
Longevity and Metabolic Health Enthusiasts
Growth hormone plays roles in metabolic health, body composition, and potentially aging markers. GHRP-6's emerging research on cellular protection and antioxidant activation makes it interesting for those interested in broader health optimization beyond just muscle growth.
Side effects
GHRP-2
Common
- Substantially increased food intake
- Gastrointestinal effects
- Feeling of warmth, drowsiness, runny nose
Uncommon
- Low blood pressure
- Raised white cell count and lactate
GHRP-6 (Growth Hormone Releasing Peptide-6)
Common
- Increased Appetite
- Mild Joint or Muscle Discomfort
- Water Retention or Mild Swelling
Uncommon
- Sleep Disturbances
- Mild Dizziness or Lightheadedness
Serious
- Allergic Reaction
Safety & evidence
GHRP-2
Evidence level
Approved diagnostic agent in Japan; no treatment approval anywhere
FDA status
Not FDA approved. Approved in Japan as 注射用GHRP科研100 (pralmorelin hydrochloride, Kaken Pharmaceutical) for the diagnosis of growth hormone deficiency only — a single 100 μg intravenous dose. There is no treatment approval for GHRP-2 in any country.
Safety overview
The largest measured effect in humans is on appetite, and it is not small: in 19 adults, food intake rose 10.2 ± 3.9% at 0.1 mcg/kg/hour (p=0.011) and 33.5 ± 5.8% at 1 mcg/kg/hour (p<0.001) against placebo, with obese participants responding as much as lean ones [7]. The Japanese diagnostic label lists abdominal rumbling, leukocytosis, a feeling of warmth, low blood pressure, nausea, gastric discomfort, abdominal distension, drowsiness and rhinorrhoea as adverse reactions — but that label covers a single 100 μg intravenous dose, not repeated use [6]. In 6 growth-hormone-deficient children given 0.3 to 3.0 mcg/kg/day for 8 months, no side effects or toxicities were observed, in a cohort far too small to detect anything uncommon [5]. One adverse signal from longer infusion: in critically ill men, GHRP-2 given alone at 1 mcg/kg/hour for 5 days raised serum lactate and white cell count by day 5, which the fuller hormonal replacement in the same trial did not [8].
Contraindications
- Pregnancy or breastfeeding — no human data
- Known hypersensitivity to pralmorelin
- Anyone for whom a 33% rise in food intake is the opposite of the goal — that is the measured effect at 1 mcg/kg/hour [7]
- There is no treatment label anywhere, so there is no authoritative contraindication list for repeated use
GHRP-6 (Growth Hormone Releasing Peptide-6)
Evidence level
Limited human trials
FDA status
Research compound
Safety overview
GHRP-6 has a relatively long research history dating back to 1981, with human studies demonstrating its ability to stimulate GH release. The good news is that animal safety studies show excellent tolerability at high doses, and the side effects reported are generally mild and reversible. However, it's not FDA-approved, so use is based on research evidence rather than pharmaceutical oversight. Always purchase from reputable sources and consider medical consultation, especially if you have existing health conditions.
Contraindications
- Known allergy or sensitivity to any component of the peptide
- Active cancer or history of cancer without medical clearance
- Severe cardiovascular disease or uncontrolled hypertension
- Acute critical illness or sepsis
Which is right for you?
Choose GHRP-2 if...
- Growth hormone optimization
- Muscle building
- Recovery enhancement
- Anti-aging
Choose GHRP-6 (Growth Hormone Releasing Peptide-6) if...
- Building lean muscle mass and improving body composition
- Recovery from intense training programs and athletic performance
- Supporting overall metabolic health and longevity markers
- Exploring novel GH-stimulation pathways for those who respond well to peptide protocols