Side-by-side · Research reference

Melanotan-IIvsP21

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

APhase 1HUMAN-REVIEWED9/43 cited

BAnimal-MechanisticHUMAN-REVIEWED8/36 cited

Melanotan-II

MC1R + MC4R agonist · Tanning + sexual response

0.25–1.0 mgPer doseDorr 1996

Phase 1Evidence levelDorr 1996

~1 hrHalf-life

SQ · Abdomen · Loading 5–7 days, then maintenance

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

Melanotan-II

P21

Primary target

MC1R (skin) + MC3R + MC4R (CNS sexual / appetite)Dorr 1996

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

Pathway

MC1R agonism → melanocyte tyrosinase → eumelanin synthesis. MC4R → autonomic sexual arousal centresDorr 1996 Simerly 2023

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

Downstream effect

Skin darkening, photo-protection, increased sexual desire / spontaneous erectionDorr 1996

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

Feedback intact?

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Origin

Cyclic 7-AA modified α-MSH analog; designed at University of ArizonaDorr 1996

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

Antibody development

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02Dosage Protocols

Parameter

Melanotan-II

P21

Loading phase

0.25–0.5 mg/day SQ × 5–7 daysDorr 1996

Builds up to visible tan.

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Maintenance

0.5–1.0 mg 1–2×/week

After visible tan develops; supports with UV exposure.

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Frequency

Daily during loading; 1–2× per week maintenance

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Lower / starter dose

0.1 mg / day

Conservative starter — assess tolerability for nausea.

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Evidence basis

Phase 1 + anecdotalDorr 1996

Animal models only

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

Duration

8–12 weeks per cycle

Not specified

Reconstitution

Bacteriostatic water; protect from light

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Timing

Evening preferred (24h tan-development cycle)

—

Half-life

~1 hour plasma; effects on melanocytes persist days

—

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

Melanotan-II

P21

Nausea

Common, especially loading phase

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Flushing

Common transient

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Spontaneous erection

Common in men — MC4R cross-effectDorr 1996

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Increased mole / freckle pigmentation

Existing moles darken; new lesions possible

—

Melanoma risk

Theoretical concern — increased melanocyte activity; CAUTION in melanoma history

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Appetite suppression

MC4R-mediated; mild

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Pregnancy / OB

Contraindicated

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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

Melanotan-II

·History of melanoma or atypical mole syndrome
·Pregnancy / breastfeeding
·Active uncontrolled hypertension

P21

·Use in humans not validated

Relative Contraindications

Melanotan-II

·Significant freckling / dysplastic nevus
·Personal or family melanoma history

P21

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

05Administration Protocol

Parameter

Melanotan-II

P21

1. Reconstitution

Add 2 mL bacteriostatic water to 10 mg vial → 5 mg/mL = 500 mcg per 0.1 mL. Light-protected.

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

2. Injection site

SQ — abdomen. 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

Evening preferred. UV exposure (sunlight or tanning bed) helps develop tan.

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4. Storage

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

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5. Needle

29–31G insulin syringe.

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