Editorial note: this article summarises published research on Melanotan I, Melanotan II and PT-141 (bremelanotide). Baclabs does not sell these compounds or any peptide; we supply bacteriostatic water and reconstitution consumables. Nothing here is medical advice.
Melanotan II, Melanotan I and PT-141 are all synthetic analogues of alpha-melanocyte-stimulating hormone (α-MSH), the 13-amino-acid hormone that drives melanin production through the melanocortin-1 receptor (MC1R). From that common origin the three went in very different directions: one became a licensed orphan medicine, one a licensed treatment for low sexual desire, and one an illegal tanning injection.
This article compares receptor pharmacology, trial evidence and UK status, answers the PT-141-for-men question from the trial record, and follows the MHRA’s position by giving no dosing information for Melanotan II. It is part of the specialised peptides cluster.
The melanocortin receptors and why selectivity matters
There are five melanocortin receptors. MC1R on melanocytes controls pigmentation; MC2R is the adrenal ACTH receptor; MC3R and MC4R in the hypothalamus regulate appetite, energy balance and sexual arousal; MC5R is involved in exocrine function. Native α-MSH is degraded within minutes, so stabilised analogues were made. Substituting D-phenylalanine and norleucine gave a linear peptide later named afamelanotide (Melanotan I). Cyclising a shorter fragment gave Melanotan II, which is more potent but far less selective, activating MC3R, MC4R and MC5R as well as MC1R. Removing the C-terminal amide from Melanotan II produced bremelanotide (PT-141), which retains MC3R/MC4R activity with much less pigmentation at the doses used. The receptor profile explains the rest: a selective MC1R agonist tans; a non-selective agonist also suppresses appetite, causes nausea and triggers erections.
| Melanotan I (afamelanotide) | Melanotan II | PT-141 (bremelanotide) | |
|---|---|---|---|
| Structure | Linear 13-mer | Cyclic 7-mer | Cyclic 7-mer, free acid |
| Main receptors | MC1R | MC1R, MC3R, MC4R, MC5R | MC3R, MC4R (some MC1R) |
| Licensed product | Scenesse 16 mg implant | None | Vyleesi 1.75 mg autoinjector (US) |
| Licensed use | Erythropoietic protoporphyria | None | HSDD, premenopausal women |
| UK status | POM, specialist centres | Illegal to sell or supply | Not licensed in the UK |
Melanotan I: afamelanotide and Scenesse
Melanotan I is afamelanotide, licensed as Scenesse for adults with erythropoietic protoporphyria (EPP), a rare genetic disorder in which protoporphyrin IX accumulates in the skin and causes severe pain on light exposure. It is supplied as a 16 mg subcutaneous implant inserted every two months by a trained clinician. In two randomised, vehicle-controlled trials in 167 patients, published by Langendonk and colleagues in the New England Journal of Medicine in 2015, afamelanotide increased the time patients could spend in direct sunlight without pain: a median 64.1 hours over 180 days versus 40.5 hours on placebo in the US study, and 6.0 hours versus 0.75 hours over 270 days in the European study [1][10]. The FDA approved it in 2019 [1]. Adverse reactions in the label are implant-site reactions (21 per cent versus 10 per cent on vehicle), nausea (19 per cent versus 14 per cent), oropharyngeal pain, cough and fatigue; because the drug can darken existing naevi and freckles, a full-body skin examination twice a year is recommended [1].
Melanotan II: what the trials found and why it was abandoned
Melanotan II was tested in a pilot phase I study in the 1990s [2] and in a double-blind, placebo-controlled crossover study in men with psychogenic erectile dysfunction, which found that it initiated erections [3]. It never progressed as a drug candidate; the erection-inducing metabolite was developed as PT-141 and the tanning programme moved to the more selective Melanotan I.
The adverse-effect profile documented in those studies and subsequent case reports is the reason. DermNet lists facial flushing, reduced appetite, nausea, vomiting and spontaneous erections as short-term effects, and darkening of existing moles, new moles, atypical melanocytic naevi, nail discolouration, rhabdomyolysis and posterior reversible encephalopathy syndrome among the serious reports, with at least one published melanoma associated with use [4]. A 2025 case series raised the possibility of a link between Melanotan II nasal sprays and oral mucosal melanoma [5].
The MHRA position
Cancer Research UK states plainly that it is illegal to sell or supply Melanotan injections in the UK and that the MHRA regards the “tan jab” as an unlicensed medicine that may not be safe [6]. In a 2024 Freedom of Information response the MHRA confirmed that injectable and nasal-spray Melanotan II products presented with medicinal claims are unauthorised medicines whose sale, supply and advertising is not permitted; that it had received 16 Yellow Card reports for Melanotan II between 2012 and 2022; and that it has repeatedly taken action to remove Melanotan products from the market for over ten years [7]. Consistent with that position, this article gives no dose, frequency or reconstitution figures for Melanotan II.
PT-141: bremelanotide and Vyleesi
PT-141 became bremelanotide. After the male erectile-dysfunction programme was halted, development refocused on women, and in 2019 the FDA licensed Vyleesi for acquired, generalised hypoactive sexual desire disorder (HSDD) in premenopausal women. The licensed regimen is 1.75 mg subcutaneously into the abdomen or thigh by autoinjector, at least 45 minutes before anticipated sexual activity, no more than one dose in 24 hours and no more than eight doses a month [8]. In the two 24-week phase 3 trials (RECONNECT, NCT02333071 and NCT02338960) in 1,247 women, bremelanotide improved desire scores and reduced distress compared with placebo [8].
The label is candid about tolerability. Nausea affected 40 per cent of women on bremelanotide versus 1.3 per cent on placebo, flushing 20.3 per cent, injection-site reactions 13.2 per cent and headache 11.3 per cent. Eighteen per cent of women stopped treatment because of adverse reactions, against 2 per cent on placebo, with nausea the most common reason. Systolic blood pressure rose by a mean 6 mmHg for a few hours after dosing, so uncontrolled hypertension and known cardiovascular disease are contraindications. Focal hyperpigmentation occurred in 1 per cent at the licensed frequency but in 38 per cent when dosed daily for eight days, more often in darker skin [8]. Vyleesi has no UK marketing authorisation.
PT-141 dosage for men: what the trials tested
The search for a “pt 141 dosage for men” has no licensed answer, because bremelanotide is not licensed for men anywhere. What exists is the trial record from the 2000s. Bremelanotide was studied in men with erectile dysfunction, including a randomised, double-blind, placebo-controlled study by Safarinejad and Hosseini published in the Journal of Urology in 2008 in men who had not responded to sildenafil [9]. The doses and response rates from that study are behind a paywall and are not reproduced here. The male programme was discontinued and the subcutaneous formulation was carried forward in women only. The only human dose with regulatory backing is the 1.75 mg subcutaneous dose in premenopausal women [8]; men using that figure are extrapolating outside the licence, with the same nausea, flushing and blood-pressure effects to expect and no male efficacy data at that dose. Licensed erectile-dysfunction treatments with far stronger evidence are available through a prescriber.
Reconstitution and diluent
Scenesse and Vyleesi are finished pharmaceutical products: an implant and a prefilled autoinjector. Neither is reconstituted. Where PT-141 is handled as a lyophilised research powder: concentration = milligrams in the vial ÷ millilitres of diluent, and each U-100 unit is one-hundredth of a millilitre. A 10 mg vial with 2 mL of diluent gives 5 mg/mL, or 50 mcg per unit; with 1 mL, 100 mcg per unit. A vial punctured more than once needs a preserved diluent; bacteriostatic water contains 0.9 per cent benzyl alcohol and is suitable for multi-dose use for up to 28 days after first puncture, as covered in the storage guide. Baclabs supplies UK-stocked bacteriostatic water in 30 mL vials; the reconstitution guide has worked examples. The GHK-Cu and Snap-8 article covers the cosmetic peptides in this cluster.
Frequently asked questions
Is Melanotan II legal in the UK?
No. It has no marketing authorisation anywhere. Cancer Research UK states that selling or supplying Melanotan injections in the UK is illegal, and the MHRA has confirmed that Melanotan II injections and nasal sprays presented with medicinal claims are unauthorised medicines that it has acted to remove from the market for over a decade [6][7].
What are the side effects of Melanotan II?
Reported effects include nausea, vomiting, flushing, appetite loss, yawning and spontaneous erections or priapism in men. Longer-term concerns are darkening of existing moles, new and atypical naevi, at least one reported melanoma, and rare reports of rhabdomyolysis and encephalopathy [4]. Unregulated products add contamination and dosing-error risks.
What is the difference between Melanotan I and afamelanotide?
They are the same molecule. Afamelanotide is the international non-proprietary name; Melanotan I was the research code. The licensed product, Scenesse, is a 16 mg implant given every two months for erythropoietic protoporphyria in specialist centres [1]. Powders sold online under the name are unlicensed and not equivalent.
Is PT-141 approved for men?
No. Bremelanotide is FDA-licensed only for premenopausal women with HSDD, at 1.75 mg subcutaneously up to eight times a month [8]. Male erectile-dysfunction trials in the 2000s were not carried to licensing [9]. There is no licensed male dose and no UK licence for any indication.
Does PT-141 cause tanning?
It can. Bremelanotide retains some MC1R activity, and the Vyleesi label reports focal hyperpigmentation of the face, gums or breasts in 1 per cent of women at the licensed frequency, rising to 38 per cent with daily dosing for eight days. It was more common in darker skin and did not always resolve [8].
References
- SCENESSE (afamelanotide) implant Prescribing Information. FDA, 2019
- Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide in a pilot phase-I clinical study. Dorr RT et al. Life Sciences, 1996
- Synthetic melanotropic peptide initiates erections in men with psychogenic erectile dysfunction: double-blind, placebo controlled crossover study. Wessells H et al. Journal of Urology, 1998
- Melanotan II. DermNet NZ
- Melanotan II nasal spray: a possible risk factor for oral mucosal malignant melanoma?. International Journal of Oral and Maxillofacial Surgery, 2025
- Tanning, fake tan and Melanotan. Cancer Research UK
- FOI 24/274: MHRA response on Melanotan II products and Yellow Card reports. MHRA, 2024
- VYLEESI (bremelanotide injection) Prescribing Information. FDA, 2019
- Salvage of Sildenafil Failures With Bremelanotide: A Randomized, Double-Blind, Placebo Controlled Study. Safarinejad MR, Hosseini SY. Journal of Urology, 2008
- Afamelanotide for Erythropoietic Protoporphyria. Langendonk JG et al. New England Journal of Medicine, 2015
Disclaimer: This content is for educational purposes only and does not constitute medical advice. Bacteriostatic water is supplied for reconstitution of substances intended for research and for use as directed by a healthcare professional. Peptides and medicines discussed here may be unlicensed in the UK or prescription-only; consult a qualified clinician before using any medicine. Baclabs does not sell peptides.