PT-141 (Bremelanotide): Research Peptide Guide for Canada

PT-141, also called bremelanotide, is a synthetic cyclic peptide made of seven amino acid building blocks joined into a closed ring. It is studied as an agonist at the melanocortin receptors, with its strongest activity at MC4R. It is supplied in Canada as a freeze-dried powder for laboratory research only.

PT-141 at a Glance

Written by the NexPept Research Team · Last updated: 2026

What Is PT-141?

PT-141 is a small synthetic peptide. A peptide is a short chain of amino acids — the same building blocks the body uses to make proteins. Where most peptides are open chains, PT-141 is a ring. Seven building blocks are joined end to end, and then a chemical bridge locks the chain into a closed loop.

That ring shape is not decoration. A floppy open chain can fold into thousands of shapes, and only one of them fits a receptor. Locking the chain into a ring means it is already holding the shape the receptor wants, which makes it bind far more strongly and survive far longer in a sample.

Its other name, bremelanotide, is the official international name. PT-141, PT141 and bremelanotide all refer to the same molecule, CAS 189691-06-3.

Where PT-141 Comes From

PT-141 was not designed from scratch. It sits at the end of a chain of modifications that started with a natural signal the body already makes.

That signal is alpha-MSH, a 13-part peptide that switches on a family of receptors called the melanocortin receptors. Alpha-MSH has two problems as a research tool: it falls apart in minutes, and one of its parts reacts with oxygen and degrades.

Scientists fixed both with two changes — swapping the oxygen-sensitive part for a stable one, and flipping another part into its mirror-image form so enzymes could no longer cut it. Then a later team cut the chain down to its essential seven parts and closed it into a ring. That gave Melanotan-2.

PT-141 is Melanotan-2 with one final change: a single chemical group swapped at the tail end of the molecule. That is the entire difference between them.

How PT-141 Is Built

The sequence is written as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. Unpacking that:

• Ac- means the front end is capped with an acetyl group. Caps protect the ends of a peptide from enzymes that chew inward from the edges.
• Nle is norleucine. It replaces methionine, the part in the natural signal that reacts with oxygen. Norleucine is nearly the same size and shape but has no sulfur, so it cannot rust.
• cyclo[...] marks the ring. The bridge runs between the Asp and Lys parts, joining their side branches rather than the main chain.
• D-Phe is a mirror-image phenylalanine. Living things build with the "left-handed" form, so enzymes only recognise that one. Flipping it makes the bond next to it uncuttable, and locks the key binding section into the right shape.
• -OH is the tail. This is the one place PT-141 differs from Melanotan-2, which ends in -NH2 instead.

PT-141 vs Melanotan-2

This is the most common point of confusion, so it is worth being precise. These are two different compounds, but only just.

They differ by about one dalton in weight. That is close enough that a Certificate of Analysis showing molecular weight will not, on its own, prove which one you have — the two numbers are nearly the same. The COA needs to name the compound and show a matching test result, not just a weight in the right range.

The Melanocortin Receptors

Receptors sit on the surface of cells and work like locks. A peptide is the key. When the right key enters the right lock, the cell responds.

There are five locks in this family, and they do different jobs in different places:

All five belong to a large family of receptors that pass their signal inward by raising a messenger molecule called cAMP inside the cell. Measuring how much cAMP rises is the standard way labs check whether a peptide has switched a receptor on, and by how much.

Research Context

PT-141 appears in laboratory work as a tool compound — something used to switch a receptor on so researchers can watch what happens downstream. Typical uses include:

• Receptor binding studies. Measuring how tightly PT-141 attaches to each of the five melanocortin receptors, usually in cells engineered to display one receptor at a time.
• cAMP signalling assays. Tracking how much the internal messenger rises after the receptor is switched on, as a measure of how strongly the peptide activates it.
• Selectivity profiling. Comparing PT-141 side by side with related compounds to work out which receptor is responsible for a given effect.
• Structure and shape studies. The PT-141 and Melanotan-2 pair differ at exactly one position, which makes them a clean way to study how a single chemical group changes receptor preference.

Storage and Handling

PT-141 ships as a freeze-dried powder. Freeze-dried, or lyophilized, simply means the water was frozen and then removed under vacuum. A dry powder is far more stable than a peptide sitting in liquid, which is why peptides are shipped this way.

Two things specific to this compound are worth knowing. It contains a tryptophan part, which is damaged by light — so amber vials or foil are sensible once it is in solution. And it contains a histidine part, which can grab onto metal ions like zinc and copper, so metal-containing buffers can throw off binding measurements.

The single biggest avoidable cause of degradation is repeated freezing and thawing. Splitting a solution into small single-use portions the first time you make it takes five minutes and protects the whole batch. Our peptide storage guide goes into more detail, and the peptide calculator helps work out volumes.

Purity and Certificates of Analysis

Here is the problem with any research peptide: a white powder looks like every other white powder. You cannot see purity, and you cannot see identity. With PT-141 specifically, you cannot tell it apart from Melanotan-2 by eye either.

The only real check is a Certificate of Analysis tied to the exact batch you received. What to look at:

• Purity. 99% or higher is the accepted benchmark. No stated figure is a warning sign on its own.
• Test methods. HPLC measures how much of the sample is the target compound. Mass Spectrometry weighs the molecule to confirm it is the compound claimed. You want both — one without the other only tells half the story.
• Molecular weight. Should land near 1,025. Be aware this does not distinguish PT-141 from Melanotan-2, since they are about one unit apart. The COA must name the compound.
• Independent lab. An outside laboratory, not the seller's own bench. A company grading its own homework proves nothing.
• Batch number. The document should match your vial, not be a generic file reused for every order.

You can view NexPept's third-party COAs on our peptide COAs page.

Sourcing PT-141 in Canada

PT-141 is supplied in Canada for laboratory research use only, with research-use-only labelling. It is not approved for human or veterinary use. Our guide to peptide regulations in Canada covers how this works.

When comparing Canadian suppliers, the same criteria apply as for any research peptide:

• Independent testing with a COA you can see before buying, not after
• Batch tracking, so your vial maps to a specific report
• Clear research-use-only labelling with no dosing or human-use claims anywhere on the site
• Domestic shipping, which avoids customs delays and long stretches at uncontrolled temperature
• Support that can actually answer a storage or handling question

Shipping matters more with peptides than with most products. A parcel held at the border for two weeks is two weeks of temperature swings. Our page on how we ship peptides in Canada explains our process.

Common Mistakes

Assuming PT-141 and Melanotan-2 are interchangeable

They are close relatives, not the same compound. PT-141 leans toward MC4R; Melanotan-2 is broad across the family. Substituting one for the other changes which receptors are switched on, and therefore what a result means.

Relying on molecular weight to confirm identity

Their weights differ by roughly one unit. A weight in the right range is consistent with either. The COA has to name the compound and show a matching chromatogram.

Leaving solution in a clear vial on a lit bench

The tryptophan part degrades under light. It happens quietly while you work. Amber vials or foil solve it.

Freezing and thawing the same vial repeatedly

Each cycle damages a little more of the peptide. Aliquot once, at the start.

Using metal-containing buffers

Histidine binds zinc and copper. In a competitive binding assay that can shift your numbers without any obvious sign that something went wrong.

Frequently Asked Questions

Key Points

• PT-141 (bremelanotide) is a cyclic 7-amino-acid peptide, CAS 189691-06-3
• It acts across the melanocortin receptors, most strongly at MC4R
• It is Melanotan-2 with one chemical group changed at the tail
• Their weights are about one unit apart, so a COA must name the compound
• Keep the powder cold, dry and dark; aliquot solutions and protect from light
• Look for 99%+ purity by HPLC and MS from an independent lab, tied to your batch
• Supplied in Canada for laboratory research use only

Related reading: Melanotan 1 vs Melanotan 2 · Melanotan-2 Research Peptide Overview · Peptide Purity & COAs Explained · Full research catalogue