MT1 (afamelanotide) is the MC1R-selective melanocortin peptide and the basis for FDA-approved Scenesse. It has a more favorable side effect profile than MT2, with nausea and flushing as the most common reactions.
Medical Disclaimer: This page is for informational and research purposes only. It does not constitute medical advice. Always consult a qualified healthcare professional before use. Research peptide MT1 is not FDA-approved for general use.
MT1 (Melanotan I, afamelanotide) is a synthetic analogue of alpha-melanocyte stimulating hormone (alpha-MSH) with high selectivity for the MC1R receptor. This receptor selectivity is the key pharmacological distinction from MT2 — by primarily activating MC1R (expressed on melanocytes), MT1 produces skin tanning with significantly fewer systemic effects than the non-selective MT2. The clinical evidence base for MT1 is substantial: it completed Phase 3 trials and received FDA approval as Scenesse for erythropoietic protoporphyria in 2019.
The most clinically significant safety concern with MT1 is its effect on melanocytic nevi (moles). By stimulating melanocyte activity broadly, MT1 can cause existing moles to darken and new moles to appear. While this has not been shown to increase melanoma risk in clinical trials, any changing moles should be evaluated by a dermatologist. This monitoring requirement is the primary reason MT1 carries a "Moderate" severity rating despite its generally favorable acute side effect profile.
| Side Effect | Frequency | Severity | Management |
|---|---|---|---|
| Nausea | Common (10–20%) | Mild | Inject in the evening. Stay hydrated. Reduce dose. Typically resolves in 1–2 weeks. |
| Flushing | Common (10–20%) | Mild | Transient. Typically resolves within 1–2 hours. Reduce dose if persistent. |
| Fatigue | Common (10–15%) | Mild | Usually transient. Inject in the evening. Reduce dose if persistent. |
| Injection site reactions | Common (15–25%) | Mild | Rotate injection sites. Apply cold compress. Ensure sterile technique. |
| Skin darkening (tanning) | Very common (intended effect) | Mild (cosmetic) | Expected effect. Dose-dependent and reversible upon discontinuation. |
| Mole darkening or new moles | Common with extended use | Moderate (monitor) | Monitor all moles. Consult dermatologist for any changing lesions. |
| Headache | Uncommon (5–10%) | Mild | Hydrate well. Reduce dose. Use OTC analgesics if needed. |
| Spontaneous erections (rare vs MT2) | Rare (MC1R selective) | Mild | Less common than MT2. Reduce dose if problematic. |
MT1's acute side effects (nausea, flushing, fatigue) are mediated through its partial activation of MC3R and MC4R at higher doses, despite its primary MC1R selectivity. MC4R activation in the hypothalamus is responsible for the nausea and appetite suppression effects. Flushing occurs through MC1R-mediated vasodilation in peripheral blood vessels. These effects are dose-dependent and typically diminish as the body adapts to the peptide.
The mole-related effects are a direct consequence of MT1's intended mechanism — widespread MC1R activation on melanocytes throughout the body, not just in sun-exposed areas. This systemic melanocyte stimulation can activate dormant melanocytes in existing nevi, causing darkening, and can stimulate new melanocyte clusters to form. The clinical significance of this effect is debated; the Scenesse Phase 3 trials did not show increased melanoma risk, but long-term surveillance data is limited.
MT1's immune-modulatory effects via MC1R may interact with immunosuppressant therapy. Monitor immune function.
MT1 increases UV sensitivity in melanocytes. Photosensitizing drugs may compound this effect.
Estrogen affects melanin synthesis. Concurrent use may alter MT1's pigmentation effects.
MT1 (afamelanotide) is generally considered to have a more favorable side effect profile than MT2. MT1 is selective for the MC1R receptor (skin pigmentation) whereas MT2 is non-selective and also activates MC3R and MC4R, which are responsible for MT2's sexual and appetite effects. MT1 has completed Phase 3 clinical trials and is FDA-approved as Scenesse for erythropoietic protoporphyria.
Nausea is the most commonly reported side effect of MT1, occurring in 10–20% of users. It is typically mild and transient, most pronounced in the first few days of use. Taking the injection in the evening and staying well-hydrated can reduce nausea severity.
MT1 stimulates melanocyte activity, which can cause existing moles to darken and new moles to appear. Any new or changing moles should be evaluated by a dermatologist. This is the most clinically significant safety concern with MT1.
Most MT1 side effects (nausea, flushing, fatigue) are transient and resolve within 24–48 hours of each injection. Skin darkening is the only persistent effect and reverses gradually over weeks to months after discontinuation.
Yes — afamelanotide (MT1) is FDA-approved as Scenesse (implant form) for erythropoietic protoporphyria (EPP), a rare photosensitivity disorder. Research peptide MT1 is a different formulation and is not FDA-approved for general use.
Medical Disclaimer: All content on this site is for educational and research purposes only. Research peptides are not FDA-approved for human use. Always consult a qualified healthcare professional before considering any peptide or supplement protocol. Nothing on this site constitutes medical advice, diagnosis, or treatment.