What is Melanotan II?

What is Melanotan II?

Melanotan II is a lab-made peptide that makes skin produce more melanin, the brown pigment that gives skin its colour. That is how the TGA describes it. A 1996 pilot study calls it a lactam-bridged cyclic heptapeptide. In plain words, it is a ring of seven amino acids held closed by a chemical bridge. The same paper says it is a modified copy of alpha-MSH with strong pigment activity in laboratory tests. A 2006 review adds two points. Melanotan II was patented and tested in clinical studies of erectile dysfunction. The earlier compound, Melanotan I, was the one tested for skin tanning.

A peptide is a short chain of amino acids. Amino acids are the same building blocks that make up proteins. The body makes many peptide hormones, and drug designers often start from one and change it. Here the starting point was alpha-MSH. Researchers changed its structure to study melanocortin signalling, the family of hormone signals that alpha-MSH belongs to.

This page does not print the amino-acid sequence. The 1996 paper gives it, so a reader who needs it should take it from the paper itself00160-9).

What is alpha-MSH, the hormone Melanotan II is based on?

Alpha-MSH is a natural hormone made of 13 amino acids. Skin cells cut it from a larger starting molecule. It drives the tan that ultraviolet light produces. It does this by fitting the melanocortin-1 receptor on melanocytes, the skin cells that make pigment. A receptor is a protein on a cell's surface that one signal fits, like a key in a lock. Alpha-MSH belongs to the melanocortins, a family of peptide hormones with several jobs in the body. Melanotan I and II are lab-made, modified copies of alpha-MSH. A 2017 review says people use them mainly to get a tan, outside medical supervision.

Alpha-MSH does more than colour skin. A 2025 review says melanocortin receptors take part in skin colour, appetite, the stress response, thinking and the body's energy balance. So a molecule that reaches these receptors can act well beyond the skin. How Melanotan II works follows that thread.

What is the difference between Melanotan I and Melanotan II?

Melanotan I and Melanotan II are two different molecules. Melanotan I is a straight chain of amino acids. Melanotan II is a shortened chain closed into a ring. Melanotan I is also called afamelanotide. It was the first modified copy of alpha-MSH, it fits the melanocortin-1 receptor, and it has a registered medicine of its own. The TGA says tanning products are often labelled Melanotan I or Melanotan II. So the two names do not describe one product. One of them has medical approvals that the other lacks. The table below sets the two side by side with PT-141, a third related molecule.

In Australia the two have separate rows in the October 2026 Poisons Standard. That is the national list that sorts medicines and poisons into classes. Schedule 4 is its prescription-only class. The research team's check on 16 October 2026 found afamelanotide as its own Schedule 4 entry. It has a registered medicine on the Australian Register of Therapeutic Goods (ARTG 327947, afamelanotide acetate). The same check found Melanotan II as a separate Schedule 4 entry. Approval of one product does not approve every preparation of a substance. Is Melanotan II legal in Australia? sets out the records.

Is Melanotan II the same as PT-141?

No. PT-141 is the research name for bremelanotide, a different molecule. A 2006 review describes it as a newer, modified version of Melanotan II. Bremelanotide also switches on melanocortin receptors. The US Food and Drug Administration (FDA) approved it as Vyleesi on 21 June 2019. The approval covers acquired, generalised hypoactive sexual desire disorder, a condition of low sexual desire, in women before menopause. The TGA reports no approved Melanotan II product in Australia. Findings for one molecule do not carry over to the other. Approval for one is not approval for the other.

The two names are easy to mix up because both molecules act on the same receptor family. Both have been linked to nausea. A 2000 report found nausea with Melanotan II, and a 2019 trial paper found nausea and flushing with bremelanotide. If a label mixes the names, check which molecule is meant. A forensic laboratory study found both Melanotan II and bremelanotide in eight unknown samples taken by police. That shows both turn up outside regulated supply.

Is Melanotan II an approved medicine?

No approved Melanotan II product was found in Australia. The TGA says Melanotan II is a prescription-only medicine. It also says Melanotan II is not approved for use as a tanning agent. No product containing it is on the ARTG, the national register of approved medicines and health products. A January 2025 TGA blog adds that melanotan tanning products have not been assessed for quality or safety. So a label cannot tell a buyer what a product contains. Prescription-only describes how the substance is classed. It does not mean an approved product exists.

In the United States, the FDA lists Melanotan II on its page of bulk substances that may carry significant safety risks in compounding. Compounding means a pharmacy mixes a medicine to order. The page, checked on 16 October 2026, says compounded drugs containing Melanotan II may pose a risk of immunogenicity for certain routes into the body. Immunogenicity means the immune system reacts against the peptide (FDA page). The Melanotan II side effects page reports the rest of that text.

What have laboratories found in products sold as Melanotan II?

TGA laboratories tested five seized nasal spray bottles sold under one brand name. All five contained Melanotan II and carried the same label. Yet the estimated amount in the highest bottle was more than twice the amount in the lowest. The TGA calls this an inconsistent strength across bottles. This finding covers those five seized bottles only. It is not a statement about every product. A separate 2021 forensic study looked at eight unknown samples that police had taken. It found Melanotan II and bremelanotide among them. Both findings show that what is in a bottle can differ from what a buyer expects.

The TGA also warns that products bought online may not contain the ingredients stated on the label. A 2017 review gives a related reason for caution. Questions remain about how these substances are prepared and given, and about what is in them, because they sit outside regulated supply.

Evidence limits

What is not known about Melanotan II?

A gap in these sources is not proof that no research exists. The half-life and binding figures are unconfirmed here. They have not been shown to be unknown to science. The study findings page sets out what the human papers did measure, and the limits of each.