Side-by-side · Research reference

HexarelinvsP21

Side-by-side comparison across mechanism, dosage, evidence, side effects, administration, and stack synergies. Citations on every claim where available.

APhase 1HUMAN-REVIEWED19/45 cited

BAnimal-MechanisticHUMAN-REVIEWED8/36 cited

Hexarelin

Hexapeptide GHRP · Cardio-tropic

100–200 mcgPer doseSmith 1996

Phase 1Evidence levelGhigo 1997

~70 minHalf-lifeSemenistaya 2010

SQ · Multiple sites · 1–3×/day

P21

CNTF-Derived Neuropeptide · Animal Model Evidence

CNTFR/gp130Primary receptorGuo 2022

Animal onlyEvidence level

NeurogenesisPrimary effectJia 2020 Mottolese 2024

SQ · Site unspecified · Frequency unknown

01Mechanism of Action

Parameter

Hexarelin

P21

Primary target

Ghrelin receptor (GHS-R1a) + cardiac CD36Smith 1996 Ghigo 1997

CNTF receptor alpha (CNTFRα) / LIF receptor (LIFR) / gp130 complex on neural stem cells

Pathway

GHS-R1a → Gαq → Ca²⁺ → GH release. CD36 engagement → direct cardio-tropic actionGhigo 1997

CNTF mimetic → CNTFRα/LIFR/gp130 heterotrimer → JAK/STAT3 signaling → neurogenesis, stem cell proliferation, neuroprotection

Downstream effect

Strong GH pulse + IGF-1 elevation; cardio-protective effects in animal MI modelsGhigo 1997

Increased neural stem cell self-renewal, globose basal cell activation (Mash1+ cells), olfactory sensory neuron regeneration, hippocampal neurogenesis, neuroprotection in developmental disorders

Feedback intact?

Yes initially; tachyphylaxis with chronic useGhigo 1997

—

Origin

Synthetic hexapeptide His-D-2-Methyl-Trp-Ala-Trp-D-Phe-Lys-NH₂Smith 1996

Small-molecule peptide mimetic derived from full-length ciliary neurotrophic factor (CNTF), designed to retain receptor activation with improved pharmacokineticsMottolese 2024

Antibody development

—

02Dosage Protocols

Parameter

Hexarelin

P21

Standard dose

100–200 mcg per injectionSmith 1996

—

Frequency

1–2× per day max (tachyphylaxis with chronic 3× daily)

—

Lower / starter dose

50 mcg per dose

—

Evidence basis

Phase 1 / Phase 2 trialsSmith 1996 Ghigo 1997

Animal models only

CDKL5 KO mice, methimazole-induced olfactory injury, CNTF-/- knockout models.Mottolese 2024 Cox 2026 Jia 2020

Duration

4–8 weeks on / 4–8 weeks off (tachyphylaxis mitigation)

Not specified

Reconstitution

Bacteriostatic water

—

Timing

Pre-sleep + fasted preferred

—

Half-life

~70 minSemenistaya 2010

—

Human dosing

—

No established protocol

No clinical trial data available.

Animal models (mice)

—

Dose and route not specified in abstractsMottolese 2024 Jia 2020

In vitro and in vivo studies demonstrate efficacy; precise dosing protocols not disclosed.

Route

—

Presumed subcutaneous or intraperitoneal (animal studies)

04Side Effects & Safety

Parameter

Hexarelin

P21

Cortisol elevation

Modest at high dosesGhigo 1997

—

Prolactin elevation

Modest at high dosesGhigo 1997

—

Hunger

Strong appetite increase via ghrelin agonism

—

Tachyphylaxis

Receptor desensitisation with chronic dosingGhigo 1997

—

Cardiac effects

Direct cardio-tropic; potential benefit in MI but unstudied in humansGhigo 1997

—

IGF-1 elevation

Strong; monitor with chronic high-dose use

—

Cancer risk

Contraindicated in active malignancy (GH/IGF-1 axis)

—

Pregnancy / OB

Avoid

—

Human safety data

—

None available

No clinical trials in humans.

Animal tolerability

—

Well-tolerated in mouse models; no toxicity reported in available abstracts

Theoretical risks

—

Uncontrolled stem cell proliferation, immune response to peptide, unknown long-term CNS effects

Absolute Contraindications

Hexarelin

·Active malignancy
·Pregnancy / breastfeeding
·Disrupted hypothalamic-pituitary axis

P21

·Use in humans not validated

Relative Contraindications

Hexarelin

·Untreated diabetes
·Severe hyperprolactinemia

P21

·Active malignancy (theoretical — neurotrophic signaling may affect tumour growth)
·Pregnancy or lactation (no safety data)

05Administration Protocol

Parameter

Hexarelin

P21

1. Reconstitution

Add 2 mL bacteriostatic water to 5 mg vial → 2.5 mg/mL = 250 mcg per 0.1 mL.

Not established. No FDA approval, no clinical trial data.

2. Injection site

SQ — abdomen or thigh. Rotate sites.

In vivo studies used systemic administration (route not specified in abstracts) in mouse models of neurodegeneration, olfactory injury, and CDKL5 deficiency disorder. In vitro studies used primary cell cultures.

3. Timing

Pre-sleep + fasted preferred. Cycle on/off to avoid tachyphylaxis.

—

4. Storage

Lyophilised: room temp, light-protected. Reconstituted: refrigerate ≤30 days.

—

5. Needle

29–31G, 4–8 mm insulin syringe.

—

06Stack Synergy

Hexarelin

+ CJC-1295 (no DAC)

Strong

View CJC-1295 (no DAC) →

Hexarelin (GHRP) + CJC-1295-no-DAC (GHRH analogue) is the higher-amplitude variant of the standard GHRH+GHRP stack. Hexarelin produces a stronger pulse than ipamorelin but with cortisol + prolactin signal — choose this stack for maximum GH amplitude when side-effect tolerance is acceptable. Cycle aggressively.

Hexarelin: 100 mcg SQ · pre-sleep
CJC-1295 (no DAC): 100 mcg SQ · same injection
Primary benefit: Maximum GH pulse amplitude (with side-effect signal)

Smith 1996 Teichman 2006

P21

— no documented stacks