Side-by-side · Research reference

Melanotan-IIvsRetatrutide

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

APhase 1Reviewed9/43 cited

BPhase 2Reviewed10/41 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

Retatrutide

Triple-receptor agonist · Phase 3

1–12 mgWeekly doseJastreboff 2023

24.2%Body-weight ↓Jastreboff 2023

~6 daysHalf-life (est)

SQ · Abdomen · Once weekly

01Mechanism of Action

Parameter

Melanotan-II

Retatrutide

Primary target

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

GLP-1R + GIPR + Glucagon receptor (triple agonism)Jastreboff 2023

Pathway

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

Triple-receptor activation → ↑insulin (GLP-1+GIP), ↓gastric emptying, ↑lipid handling, ↑energy expenditure (glucagon component)Jastreboff 2023

Downstream effect

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

Maximal weight loss across class. Glucagon component drives lipolysis and energy expenditure beyond GLP-1+GIP aloneJastreboff 2023

Feedback intact?

—

Origin

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

Synthetic peptide engineered for balanced affinity at three incretin / glucagon receptorsJastreboff 2023

Antibody development

—

02Dosage Protocols

Parameter

Melanotan-II

Retatrutide

Loading phase

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

Builds up to visible tan.

—

Maintenance

0.5–1.0 mg 1–2×/week

After visible tan develops; supports with UV exposure.

—

Frequency

Daily during loading; 1–2× per week maintenance

Once weekly

Lower / starter dose

0.1 mg / day

Conservative starter — assess tolerability for nausea.

—

Evidence basis

Phase 1 + anecdotalDorr 1996

Phase 2 trial; Phase 3 ongoingJastreboff 2023

Duration

8–12 weeks per cycle

Indefinite for chronic indication (presumed)

Reconstitution

Bacteriostatic water; protect from light

Investigational; not commercially available

Timing

Evening preferred (24h tan-development cycle)

Any time of day

Half-life

~1 hour plasma; effects on melanocytes persist days

~6 days (estimated from class)

Standard dose

—

12 mg / week (max efficacy)Jastreboff 2023

Phase 2 trial dose. Phase 3 dosing TBD.

Titration schedule

—

2 mg → 4 mg → 8 mg → 12 mg over 16 weeks

04Side Effects & Safety

Parameter

Melanotan-II

Retatrutide

Nausea

Common, especially loading phase

—

Flushing

Common transient

—

Spontaneous erection

Common in men — MC4R cross-effectDorr 1996

—

Increased mole / freckle pigmentation

Existing moles darken; new lesions possible

—

Melanoma risk

Theoretical concern — increased melanocyte activity; CAUTION in melanoma history

—

Appetite suppression

MC4R-mediated; mild

—

Pregnancy / OB

Contraindicated

Avoid (insufficient data)

GI symptoms

—

Nausea, vomiting, diarrhea (very common, dose-dependent)Jastreboff 2023

Heart rate

—

↑ resting HR (3–7 bpm at 12 mg)Jastreboff 2023

Glucose handling

—

Glycemic improvement; rare hyperglycemia from glucagon component

Pancreatitis risk

—

Class warning

Thyroid C-cell tumours

—

Class warning (presumed)

Absolute Contraindications

Melanotan-II

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

Retatrutide

·MTC personal or family history (presumed class effect)
·Pregnancy / breastfeeding

Relative Contraindications

Melanotan-II

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

Retatrutide

·Severe gastroparesis
·History of pancreatitis
·Severe cardiovascular disease (HR signal)

05Administration Protocol

Parameter

Melanotan-II

Retatrutide

1. Reconstitution

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

Investigational peptide. Research vials reconstituted with bacteriostatic water per label.

2. Injection site

SQ — abdomen. Rotate sites.

SQ — abdomen, thigh, or upper arm. Rotate weekly.

3. Timing

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

Once weekly, same day.

4. Storage

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

Refrigerate 2–8 °C. Light-protected.

5. Needle

29–31G insulin syringe.

27–31G, 4–8 mm insulin syringe.