What is PT-141?

PT-141 is a synthetic analogue of alpha-melanocyte-stimulating hormone (alpha-MSH) that acts as an agonist at melanocortin receptors, including MC3R and MC4R. ^[12] Palatin Technologies developed it. ^[3] PubChem files bremelanotide, PT-141 and PT 141 as synonyms for one compound. ^[4]

Its family tree explains most of its chemistry. In 1989, University of Arizona chemists designed a class of cyclic lactam fragments of alpha-MSH that were up to 100-fold more potent than the natural hormone in a lizard skin assay. ^[13] One of those fragments became Melanotan II. A 2006 review by University of Arizona authors describes PT-141 as a newer Melanotan II analogue from Palatin. ^[14]

The research question that drove its development was sexual function. Early work in rats and men looked at erectile responses, and later trials moved to women with low sexual desire. The 10mg PT-141 vial with its batch certificate sits in our hormone research peptides range.

PT-141 binds and activates melanocortin receptors, a family of G protein-coupled receptors that respond to alpha-MSH. A 2022 review from authors at Palatin, AMAG and two universities describes bremelanotide as a nonselective agonist across several receptor subtypes, with MC4R the most relevant at the exposures used in trials. ^[1]

MC4R is concentrated in the hypothalamus, in a region called the medial preoptic area. The same review states that animal studies suggest bremelanotide acts on MC4R there and increases dopamine release. ^[1] The rat work behind that idea is specific. In a 2004 study, PT-141 increased solicitation behaviour in female rats without changing lordosis, pacing or general movement. ^[15] In male rats, it activated hypothalamic neurons, measured as a rise in c-Fos staining. ^[12]

Structural biology added a molecular picture in 2021. A Chinese group solved high-resolution structures of full-length MC4R bound to its G protein and to four agonists, bremelanotide among them. They reported a conserved binding mode for peptide agonists. ^[16]

An independent group tested the dopamine idea in 2025, in female Syrian hamsters. They found that bremelanotide left melanocortin receptor expression in the reward pathway unchanged and did not increase sexual reward in a place-preference test. They concluded that it does not act on the VTA to nucleus accumbens reward circuit. ^[17] The mechanism in people is still inferred from animals.

PT-141 is a seven-residue peptide closed into a ring by a lactam bond between the side chains of aspartic acid (position 2) and lysine (position 7). The N-terminus carries an acetyl group, the first residue is norleucine, the fourth is D-phenylalanine, and the C-terminus is a free carboxylic acid. ^[4]

We checked each value against PubChem on 29 September 2026. ^[4][5] PubChem's systematic name spells the sequence out as N-acetyl-norleucyl-aspartyl-histidyl-D-phenylalanyl-arginyl-tryptophyl-lysine with a (2->7) lactam, and we decoded the one-line sequence from it.

Two details matter when you read a certificate. First, research peptides usually arrive as salts, and the acetate form of bremelanotide weighs 1085.2 g/mol against 1025.2 g/mol for the free peptide. ^[5] A lab reporting peptide mass by mass spectrometry measures the peptide ion, so expect a value near the free-base mass. Second, the CAS number printed on a label can be either the free-base number or the acetate number. Both describe PT-141.

PT-141 has been examined in rats, hamsters, cell lines and human trials, and the human trials are the largest body of work. Early studies (2003 to 2006) tested erectile responses in men and arousal in women. Later phase 2b and phase 3 trials enrolled premenopausal women with hypoactive sexual desire disorder.

Every finding above describes what a study reported for its own population, using the developer's material under trial conditions. None of it is a claim about a research vial.

The PT-141 evidence base is large for a research peptide and narrow in who produced it. Palatin Technologies and AMAG Pharmaceuticals funded the RECONNECT trials, ^[2] and most mechanism reviews come from the same companies and their collaborators. ^[1]

Five limits are worth stating plainly.

1. Independent reanalysis found small effects. A 2021 meta-analysis based on the US regulatory file reported that 72.72% of outcomes listed in the trial plans went unreported and that stopping because of adverse events was higher on bremelanotide (odds ratio 11.98). ^[24] A 2024 follow-up analysed 8 of 11 registered efficacy outcomes that had never been published and found effect sizes from nil to small. ^[7]
2. The trial population was narrow. RECONNECT enrolled premenopausal women with a mean age of 39. Of them, 85.6% were white and 96.6% came from US sites. ^[2]
3. Two trials in the literature carry integrity flags. A 2008 trial in women with arousal disorder was retracted after its author did not supply the original data. ^[25] A 2008 trial in 342 men carries an expression of concern published in 2023. ^[26] Neither can support a conclusion.
4. The mechanism in people is inferred. The dopamine explanation rests on animal studies, ^[1] and the 2025 hamster study found no action on the reward circuit. ^[17]
5. No published trial used research-grade material. Every human study used the developer's product. Police seizures analysed in Italy contained bremelanotide and Melanotan II that needed high-resolution mass spectrometry to identify. ^[27] What is in any research vial is a separate question, and a batch certificate exists to answer it.

Nausea, flushing and headache were the most common adverse events in the phase 3 trials, each reported at 10% or more in both studies and more often than with placebo. ^[2] A 2022 review of the whole development programme, covering 3,500 people in 43 studies, gives the pooled double-blind figures from 1,247 phase 3 participants. ^[8]

The same review reported these findings: ^[8]

• Nausea was the most common reason participants stopped.
• There were no deaths, and a few participants had serious adverse events.
• Focal hyperpigmentation (darkened patches of skin) was rare under the approved labelling. It appeared in more than one-third of participants after exposure on up to 16 consecutive days.
• Ambulatory monitoring found small, transient but statistically significant rises in blood pressure.
• 70% of the bremelanotide group moved into the open-label phase, against 87% of the placebo group.

The dedicated blood pressure trial in 397 women reported systolic rises of 2.4 to 3.2 mmHg above placebo, with peaks that usually lasted under 15 minutes and falls in heart rate of 4.6 to 4.7 beats per minute in the highest group. ^[21] In the 52-week extension, the adverse events judged related to the study drug were nausea (40.4%), flushing (20.6%) and headache (12.0%). ^[22] These are clinical-trial observations in specific populations, reported as the published record.

PT-141 has no entry in the Poisons Standard. We searched the June 2026 instrument (F2026L00633), in force from 1 June 2026, for bremelanotide and PT-141 and found neither. Schedule 4 runs straight from BPC-157 to brentuximab vedotin, where bremelanotide would sit, and Melanotan II has its own Schedule 4 entry. ^[9] A compound with no entry is described as not named in the Poisons Standard. That description says nothing about whether a product is lawful to supply.

PT-141 is also not a registered medicine in Australia on the record we checked. A search of the Australian Register of Therapeutic Goods for bremelanotide on 29 September 2026 returned no matching results. ^[10] The TGA states that "research use only" or "not for human use" disclaimers do not change whether a product is regulated as a therapeutic good. ^[28] Our guide to peptide law and the Poisons Standard explains how scheduling and the ARTG fit together.

For sport, PT-141 is not named on the WADA 2026 Prohibited List, effective 1 January 2026. ^[11] The List's S0 class covers substances with no current approval by any governmental health authority. A 2025 paper still describes bremelanotide as approved by the US Food and Drug Administration, ^[17] which places it outside that wording. WADA revises the List every year, so check the current edition.

PT-141 and Melanotan II share one ring and differ at one atom group: PT-141 ends in a carboxylic acid and Melanotan II ends in an amide. ^[4][6] That small change separates their legal status, their evidence and their identity test.

The identifiers come from PubChem ^[4][6] and the scheduling from the June 2026 instrument. ^[9] The monoisotopic masses differ by 0.984 Da, which is our own subtraction of the two PubChem values. A mass spectrometry result on a PT-141 certificate should land on the PT-141 figure. A result near 1023.5 points to Melanotan II. Melanotan II has its own product page and batch certificates.

Store lyophilised PT-141 sealed, dry, dark and frozen, and keep a reconstituted solution cold and protected from light. No published real-time stability study covers research-grade PT-141, so this guidance combines general peptide handling with one forced-degradation study of bremelanotide.

That 2026 study stressed bremelanotide acetate with acid, base, water, oxidation, heat and light. It found lower degradation in acid than in base and significant susceptibility to oxidation, with degradation under heat and light as well. The authors characterised eight degradation products, formed through deacetylation, peptide-bond hydrolysis, oxidation and epimerisation. ^[29]

General guidance points the same way. Sigma-Aldrich advises -20°C for short-term storage and -80°C for longer storage, away from bright light, and notes that sequences containing C, M or W are prone to air oxidation. ^[30] PT-141 contains one tryptophan (W). Keep vials capped, let them reach room temperature before opening, and return them to the cold promptly.

For solvents, the same guide suggests sterile distilled water or sterile dilute acetic acid (0.1%) for a stock solution. ^[30] We stock BAC Water (sterile water with 0.9% benzyl alcohol) and dilute acetic acid, each in 3ml vials for A$8. Label each vial with the batch number, solvent, concentration in mg per mL and date. Our peptide storage guide covers temperatures and freeze-thaw damage, and the reconstitution guide covers solvent choice and concentration arithmetic.

Peptides Collective sells PT-141 for laboratory research use only, as lyophilised powder in 10mg vials from A$53. Stock ships from Western Australia with tracking.

An independent lab tests every batch before it goes on sale, for purity by HPLC and identity by mass spectrometry. The certificate is published under the batch number printed on the vial. Search that number in our certificate of analysis library and match the report to the vial in your hand.

Read the certificate against the tables above. The identity result should match a peptide of about 1025.2 g/mol (1024.52 Da monoisotopic), and the gap to Melanotan II is about 1 Da. Our guide on how to read a peptide certificate of analysis explains the HPLC trace and the mass spectrum. The PT-141 product page links the certificate for the current batch.

PT-141 is bremelanotide, a cyclic seven-residue melanocortin agonist of 1025.2 g/mol that differs from Melanotan II only at its C-terminus. Its human record is large and developer-funded, and independent reanalysis reads the benefit as modest, with nausea the dominant adverse event. In Australia it has no Poisons Standard entry and no ARTG listing, and WADA's 2026 List does not name it. For a research vial, the batch certificate and its mass result settle what is inside.