Melanocortin peptides
Melanocortins are α-MSH–derived peptides that signal through five known G-protein-coupled receptors (MC1R–MC5R), each with distinct tissue distribution and physiology. Pigmentation (MC1R), adrenal steroidogenesis (MC2R), satiety and energy expenditure (MC3R/MC4R), and exocrine function (MC5R) are governed by different members of the family. Research interest in this class divides cleanly along receptor selectivity: broad-spectrum agonists like Melanotan II hit MC1, MC3, MC4, and MC5 simultaneously, while selective agonists like setmelanotide target MC4R alone and PT-141 (bremelanotide) is MC4R-biased.
Receptor map
| Receptor | Primary tissue | Function |
|---|---|---|
| MC1R | Melanocytes | Eumelanin synthesis (skin darkening) |
| MC2R | Adrenal cortex | ACTH receptor — cortisol synthesis |
| MC3R | Hypothalamus, periphery | Energy homeostasis, fasting response |
| MC4R | Hypothalamus, brainstem | Satiety, energy expenditure, sexual response |
| MC5R | Exocrine glands | Sebum and sweat secretion |
PT-141 (bremelanotide)
- What it is: a cyclic heptapeptide derived from Melanotan II by removing the C-terminal amide and adjusting cyclization, producing a compound that is essentially inactive at MC1R but retains MC4R agonism.
- Mechanism: central MC4R activation in hypothalamic and paraventricular nuclei drives sexual-response pathways independent of the vascular nitric-oxide pathway that PDE5 inhibitors target. This makes its mechanism non-overlapping with sildenafil-class compounds.
- Half-life: ~2 hours after subcutaneous dosing.
- Known effects: transient blood-pressure elevation (clinically labeled — ~6 mmHg systolic), nausea (the dominant tolerability issue at higher doses), and a slight skin-darkening signal at high cumulative exposure despite MC1R inactivity, possibly via low-level residual MC1R binding.
- Status: FDA-approved as Vyleesi for hypoactive sexual desire disorder in premenopausal women; not approved for male indications.
Melanotan II
- What it is: a synthetic cyclic heptapeptide α-MSH analog — non-selective agonist at MC1R, MC3R, MC4R, and MC5R.
- Mechanism: MC1R drives the pigmentation effect (eumelanin synthesis); MC4R drives appetite suppression and the same sexual-response pathway as PT-141; MC5R can drive sebaceous activity.
- Half-life: ~1 hour subcutaneous.
- Known safety considerations: the most documented of any peptide in this class. Reports include rapid darkening and growth of existing nevi, appearance of new pigmented lesions, gastrointestinal effects, and case reports of melanoma diagnosed in users — a strong reason it is sold strictly for research and is not approved for human use anywhere.
- Status: unapproved everywhere; widely flagged by regulators (FDA, MHRA, TGA, EMA) with consumer warnings.
Melanotan I (afamelanotide)
- What it is: a linear 13-amino-acid α-MSH analog, more selective for MC1R than Melanotan II.
- Delivery: in clinical use, delivered as a sustained-release subcutaneous implant (Scenesse).
- Status: approved as Scenesse by the EMA and FDA for erythropoietic protoporphyria (EPP) — a photoprotective indication. Not approved for cosmetic tanning.
Setmelanotide
- What it is: a selective MC4R agonist with eight amino acids, designed to specifically restore MC4R signaling in patients with rare monogenic obesity syndromes (POMC, PCSK1, LEPR deficiency, Bardet-Biedl syndrome).
- Mechanism: MC4R agonism drives satiety and increased energy expenditure via hypothalamic pathways — bypasses the upstream leptin/POMC defects that cause these syndromes.
- Half-life: ~11 hours; daily subcutaneous dosing.
- Status: FDA- and EMA-approved as Imcivree for the specific monogenic obesity indications listed above; not approved for general weight loss.
Safety considerations specific to this class
Melanocortin research carries a few distinctive risk signals that don't apply to most other peptide classes:
- Pigmentation changes are not reversible. MC1R-driven darkening of existing nevi and appearance of new pigmented lesions has been reported with non-selective agonists (Melanotan II in particular).
- MC1R/melanoma signal. Case reports and dermatology literature have flagged melanoma in Melanotan II users. The mechanistic relationship is unsettled but the signal is consistent enough that any research touching MC1R agonism warrants attention.
- Cardiovascular: transient blood-pressure rise is documented even with the more selective PT-141.
- Nausea is dose-limiting across the class.
Reconstitution and storage
Standard cold-chain peptides — reconstitute with BAC water, store at 2–8 °C, use within 30 days. Most research protocols dose in the 0.25–2 mg range subcutaneously depending on the compound. Full per-vial math is in the dosage protocols guide; cold-chain rules in the storage & handling guide.
Safety, risks & legal notice
Read before ordering or conducting any research
For laboratory research only
Every compound described on this page is sold and provided strictly as a research-grade reagent for in-vitro and animal-model studies. These products are not intended for human consumption, cosmetic use, dietary supplementation, or any clinical or therapeutic application. By purchasing, you represent that you are a qualified researcher, laboratory, or educational institution with appropriate facilities and oversight.
Not FDA-approved or evaluated
Some compounds in this class have limited regulatory approvals for specific indications (PT-141 (bremelanotide) for HSDD; afamelanotide (Scenesse) for EPP; setmelanotide (Imcivree) for specified monogenic obesity). However, the research-grade materials supplied here are not manufactured, labelled, or verified for those approved uses, and we make no claims regarding their safety or efficacy outside laboratory research.
No medical, clinical, or dosing advice
Dr Jays Peptides does not employ physicians, pharmacists, or clinical researchers. Nothing on this page — including dosage figures, reconstitution math, or mechanism descriptions — constitutes medical advice, a prescribing recommendation, or instructions for self-administration. If you are considering any peptide for personal use, consult a licensed healthcare provider who can evaluate your individual risk factors, medication interactions, and monitoring needs.
Class-specific risk signals
- Pigmentation changes are not reversible: MC1R-driven darkening of existing nevi and appearance of new pigmented lesions has been reported with non-selective agonists (Melanotan II in particular). Some users report permanent skin darkening even after cessation.
- Melanoma signal: multiple case reports and dermatology literature have flagged melanoma in Melanotan II users. The mechanistic relationship (whether causative or coincident) is unsettled, but the signal is consistent enough that any research touching MC1R agonism warrants heightened dermatological surveillance.
- Cardiovascular: transient blood-pressure rise (~6 mmHg systolic) is documented even with the more selective PT-141. In subjects with hypertension or cardiovascular disease, this constitutes a meaningful acute risk.
- Nausea and vomiting: dose-limiting across the entire melanocortin class. PT-141 in particular has a high incidence of nausea at therapeutic-equivalent doses.
- Appetite suppression and metabolic effects: MC4R agonism can produce significant anorexia and weight loss. In research models, this must be monitored to prevent malnutrition or unintended metabolic stress.
- Spontaneous sexual arousal (PT-141): the mechanism is central rather than vascular, producing unpredictable onset and duration that can be distressing outside a controlled research setting.
General risk factors
- Purity and contamination: Research peptides are not manufactured to pharmaceutical-grade GMP standards. Even high-purity lots may contain trace endotoxins, residual solvents, or unrelated peptide sequences.
- Stability and degradation: Improper storage, repeated freeze–thaw cycles, or use beyond recommended reconstitution windows can produce degraded products with unknown toxicology.
- Immunogenicity: Foreign peptides can elicit antibody responses; repeated administration may cause allergic reactions or neutralizing antibodies that alter pharmacokinetics in unpredictable ways.
- Drug interactions: Peptides may potentiate or antagonize prescription medications, herbal supplements, or other research compounds. No systematic interaction data exists for most of these molecules.
- Pregnancy, lactation, and pediatric populations: Zero safety data. Absolute contraindication for use in these populations.
Legal status & buyer responsibility
The legal status of research peptides varies by country, state, and municipality. It is the buyer's sole responsibility to understand and comply with all applicable laws, regulations, and institutional policies in their jurisdiction before ordering. Dr Jays Peptides ships products with accurate customs declarations; buyers are responsible for any import duties, inspections, or seizures. We reserve the right to cancel any order where we believe the buyer lacks legitimate research intent or where shipment would violate local law.
Limitation of liability: To the maximum extent permitted by law, Dr Jays Peptides and its affiliates, suppliers, and agents disclaim all liability for any injury, illness, adverse reaction, or loss arising from the purchase, handling, or use of any product described on this page. This includes liability for negligence, product defect, mislabeling, or failure to warn. By proceeding with a purchase, you agree to indemnify and hold harmless Dr Jays Peptides from any claims, damages, or expenses related to your research activities.