Source comparison
Melanotan-2 PT-141 Protocol Research: Structural Comparison
Chemical Structure Linear heptapeptide (Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2) Cyclic heptapeptide (Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 with lactam bridge) Cyclisation reduces MC1R affinity by ~70%, altering adverse event profile Receptor Selecti
This comparison does not assign a generated winner or score.
- Chemical Structure
- Linear heptapeptide (Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2)
- Cyclic heptapeptide (Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2 with lactam bridge)
- Cyclisation reduces MC1R affinity by ~70%, altering adverse event profile
- Receptor Selectivity
- Non-selective: MC1R–MC5R, strongest at MC4R (Ki = 0.2nM)
- MC4R-preferential: 25-fold selectivity over MC1R
- PT-141 allows CNS-focused protocols with fewer peripheral effects
- Half-Life
- ~33 hours (sustained plasma levels 4–5 days)
- 2.7 hours (clears within 12–16 hours)
- Melanotan-2 requires 2–3x weekly dosing; PT-141 is on-demand
- Typical Research Dose
- 0.25–1.0mg subcutaneous, 2–3 times weekly
- 1.75mg subcutaneous, single as-needed dose
- Higher single-dose for PT-141 compensates for rapid clearance
- Nausea Incidence
- 50–60% at doses >0.5mg
- 40% at 1.75mg therapeutic dose
- MC1R-mediated GI effects higher with Melanotan-2
- Skin Pigmentation
- Dose-dependent darkening starts at 0.25mg within 7–14 days
- Minimal darkening even at 2.0mg (MC1R sparing)
- Protocols using Melanotan-2 must screen for photosensitivity
- FDA Development Status
- No Phase 3 trials; development discontinued in early 2000s
- FDA-approved (2019) for hypoactive sexual desire disorder
- PT-141 has regulatory pathway; Melanotan-2 does not
- Bottom Line
- Broad melanocortin activation with predictable off-target effects. Useful for research requiring sustained receptor occupancy but requires careful adverse event management
- Selective MC4R agonism with short-duration effect. Ideal for sexual function research where on-demand dosing and reduced nausea are priorities