Melanotan I vs Melanotan II: Selectivity, Not Strength

The short version: Melanotan I and Melanotan II are not one compound at two strengths. They are different molecules, built from the same hormone by two opposite design decisions. One of them became a licensed medicine. The other became the popular one. Those two facts are related.

Start with the people who can’t go outside

There is a rare inherited disorder called erythropoietic protoporphyria. For the people who have it, sunlight is not uncomfortable — it is painful. Minutes of daylight can mean hours of burning. Most of them organise their entire lives around avoiding the middle of the day.

One of the two compounds in this article is an approved treatment for that condition, in several countries. The other has never been approved anywhere, for anything.

They are one numeral apart on the label.

Both start from the same signal

Skin colour is not decided by the skin. It is decided by a signal. A hormone called α-MSH tells pigment cells to produce melanin, and those cells do as they are told.

α-MSH itself is useless to study. The body destroys it within minutes. So in the 1980s, researchers set about building versions that would survive long enough to observe.

Two came out of that work. Here is where they split.

Melanotan I kept the shape

Melanotan I stayed close to the original: a linear chain of 13 amino acids, modified for stability. It acts on MC1R — the receptor sitting on pigment cells. One receptor, one job.

That narrowness is why it could be developed as a medicine. A molecule that does one predictable thing can be taken through trials, because you can measure whether it did the thing. Under the name afamelanotide, it was, and it is now licensed for the disorder described above.

Very little else in this category has been near a regulator. This one has a dossier assembled by people with no commercial interest in the answer.

Melanotan II cut it down

Melanotan II went the other way. Roughly half the length — 7 amino acids — and closed into a ring rather than left as a chain.

Shortening it made it less fussy about what it binds to. Alongside MC1R, it acts on MC3R and MC4R: receptors associated with appetite and arousal pathways, not pigment.

It never completed clinical development. It is not approved in any country.

The uncomfortable part

Melanotan II is far more widely discussed than Melanotan I. Not despite the extra receptors — because of them.

Acting on three receptors instead of one produces a wider spread of reported observations, and that spread is what most of the attention is actually about. People are not accidentally choosing the messier molecule. They are choosing it on purpose.

Which is fine, so long as nobody pretends the two halves are separable. A molecule loose enough to hit three receptors is harder to predict than one that hits a single receptor, and the tolerability complaints reported for Melanotan II track exactly that looseness. You do not get the breadth without the unpredictability. It is one property with two names.

Which is why the warnings differ

Nausea and facial flushing are the two effects most commonly reported with Melanotan II. They are generally described as short-lived, and they are the most common reason people abandon it.

The concern that matters more is the slower one. Melanocortin signalling acts on pigment cells, and dermatologists have raised concerns about existing moles darkening or changing in people who have used melanotan compounds. There are published case reports. Nobody has established how often it happens — which is itself part of the problem, because an unapproved compound generates no systematic safety data for anyone to count.

Melanotan I is not exempt from that pathway; it acts on the same receptor on the same cells. The difference is that its safety profile was assembled by regulators reviewing trial data, rather than inferred from forum posts after the fact.

If you have a lot of moles, this is the distinction worth understanding before choosing, not after.

And one of them has no approved dose

This follows directly from the approval gap, and it deserves stating on its own because it is the part most often skipped.

Afamelanotide went through clinical development. That process establishes and publishes a dose, an administration schedule and a monitoring standard, because approval cannot be granted without them.

Melanotan II never completed that process. So there is no established dose for it, no reviewed schedule, and no monitoring standard. Any number quoted for it was decided by whoever quoted it.

That is not an accusation against any particular source. It is a description of what does and does not exist — and it is the single most useful thing to know about the compound.

Side by side

	Melanotan I	Melanotan II
Structure	Linear, 13 amino acids	Cyclic, 7 amino acids
Receptors	MC1R	MC1R, MC3R, MC4R
Predictability	Narrow, one target	Broad, three targets
Regulatory status	Licensed in several countries as afamelanotide	Not approved anywhere
Supplied as	Melanotan I 10mg (lyophilised)	MT-2 10mg (lyophilised)

There is usually a third option

If the question is about MC1R, the selective molecule is the one built for it — and it is the one with the dossier.

If the question is about MC4R, then Melanotan II is a blunt instrument, because MC4R is only one of the three things it does. There is a compound designed specifically for MC4R that did complete approval: bremelanotide, known in research contexts as PT-141. It arrived at that receptor deliberately rather than as a side effect of a truncated chain.

So the real question was never “which is stronger”. It is “which receptor am I actually asking about” — and for most answers, a selective molecule exists.

If you remember one thing: these two differ by selectivity, not strength. One hits a single receptor and became a medicine. The other hits three and never did — and that is precisely why it is the popular one.

A note on framing

Everything above describes molecular structure, receptor targets, and regulatory status — the published record. None of it describes use, dosing, or outcomes in people or animals, and none of it should be read as guidance of that kind. These are research-grade materials intended for laboratory study only.

Where JP fits

JP Research supplies all three as research-grade lyophilised material: Melanotan I 10mg, MT-2 10mg and PT-141 10mg — the selective one, the promiscuous one, and the MC4R-specific one the article ends on. None of the three has an independent report on file at present; where we hold one for a compound it is published in full and linked on that product’s page. Browse the catalogue to compare the rest of the range.