PT-141 in men: a central mechanism upstream of the vascular pathway

Key points

• Bremelanotide acts on melanocortin receptors in the central nervous system, mainly MC4R, upstream of the vascular pathway that PDE5 inhibitors use [1][2][3].
• In healthy men and men with erectile dysfunction, the intranasal route was associated with a significant erectile response versus placebo at doses above 7 mg, with onset at about 30 minutes [6].
• The subcutaneous route produced significant erections in men with an inadequate response to 100 mg sildenafil [7].
• The largest trial in men (342 participants) has carried a journal expression of concern since 2023 [9].
• The approved drug (Vyleesi) is not indicated in men, and its label warns of transient blood pressure increases, nausea and focal hyperpigmentation [13].

US status (October 2026): Approved as Vyleesi for premenopausal women with acquired, generalized HSDD, and not for men; a 503A pharmacy may compound it for a named patient, subject to the copy rules. See the PT-141 status page.

PT-141 is one of the few molecules with controlled data in men that acts before erectile tissue, in the hypothalamus. The male trials are small, phase 1 to 2, and date from 2004 to 2008, and the largest is under an expression of concern. Any use in men is off-label for a drug whose label lists blood pressure, nausea and pigmentation warnings.

PT-141 acts in the brain, upstream of erectile tissue

PDE5 inhibitors act in erectile tissue: they amplify a response that has already started. Bremelanotide (PT-141) works further upstream. It is a synthetic α-MSH analog that acts as an agonist at the MC3R and MC4R melanocortin receptors, which are expressed mainly in the central nervous system [1]. That is why the urology literature groups it with centrally acting agents, alongside the dopamine, serotonin and testosterone systems [14]. This article focuses on men and on mechanism. The shared origin with melanotan II and the approval in women are covered in Melanotan II and PT-141: chemical cousins, opposite stories.

Laboratory work tied erection to hypothalamic MC4R

The role of MC4R in erection was described with genetic and pharmacological tools. A Merck team showed in 2002 that a selective MC4R agonist increased erectile activity induced by cavernous nerve stimulation in normal mice and had no such effect in mice lacking the receptor. Copulatory behavior was reduced in mice without MC4R. The receptor was expressed in human and rat penis, in rat spinal cord, hypothalamus and pelvic ganglion, and in nerve fibers of the glans. It was absent from rat primary corpus cavernosum smooth muscle cells [2].

With PT-141 itself, systemic administration in rats activated hypothalamic neurons (increased c-Fos), in the same region that connects to the corpus cavernosum in pseudorabies virus tracing studies. In rats and nonhuman primates it produced erections [1]. Bremelanotide activates several melanocortin receptor subtypes, with MC4R the most relevant at therapeutic doses. In the brain, MC4R is expressed mainly in the medial preoptic area (mPOA) of the hypothalamus [3]. The current hypothesis, based on animal studies, is that it activates presynaptic MC4Rs in that region and increases the release of dopamine, an excitatory neurotransmitter of sexual desire [3].

• About 30 min: onset of first erection with intranasal PT-141 in men [6]
• Above 1.0 mg: subcutaneous dose with a significant erectile response in healthy men [7]
• 342: sildenafil non-responders in the largest published trial [9]

Melanotan II came first

Clinical interest began with melanotan II, the compound PT-141 derives from. In a double-blind crossover trial in 10 men with psychogenic erectile dysfunction, 8 of 10 developed clinically apparent erections. Mean duration of tip rigidity above 80% was 38.0 minutes versus 3.0 with placebo (p = 0.0045) [4]. In 10 men with organic risk factors, the compound initiated patient-reported erections after 12 of 19 injections versus 1 of 21 with placebo, and reported sexual desire was higher. Nausea was frequent, and 4 of 19 injections were associated with severe nausea [5].

The PT-141 trials in men

Intranasal route (Diamond, 2004). In healthy men and in patients with mild-to-moderate erectile dysfunction who responded to sildenafil, the RigiScan-measured erectile response was statistically significant versus placebo at doses above 7 mg, with the first erection at about 30 minutes. Half-life was 1.85 to 2.09 h. Flushing and nausea were the most common adverse events. No maximum tolerated dose was identified [6].

Subcutaneous route (Rosen, 2004). In healthy men without visual stimulation, doses of 0.3 to 10 mg produced a significant erectile response above 1.0 mg. In patients with an inadequate response to 100 mg sildenafil, both 4 and 6 mg produced a significant response versus placebo in a crossover design [7]. This is the finding that matters most clinically: a different mechanism that worked where the vascular pathway fell short.

Combination with sildenafil (Diamond, 2005). In 19 men who responded to a PDE5 inhibitor, 7.5 mg intranasal PT-141 plus 25 mg sildenafil produced a greater erectile response than sildenafil alone, with no new or more frequent adverse events than with either drug alone [8].

Sildenafil non-responders (Safarinejad and Hosseini, 2008). In 342 men, 10 mg intranasal was associated with positive clinical results in 33.5% versus 8.5% with placebo (p = 0.03), with more adverse events in the active group [9]. Read this trial with caution. In 2023 the journal published an expression of concern about the article [9], and another bremelanotide trial by the same author, in women, was retracted [10].

Development moved to women and the subcutaneous route

The intranasal route had two problems. According to White and colleagues, absorption was highly variable, so some patients received more exposure than needed and others less, and the formulation “could elevate BP in both men and women” [11]. The program moved to the more predictable subcutaneous route and to hypoactive sexual desire disorder in premenopausal women [11]. The two RECONNECT phase 3 trials enrolled 1,267 women and showed increases in desire (+0.35) and reductions in distress (-0.33) versus placebo, both P < 0.001 [12]. FDA approved Vyleesi in 2019 for that indication [13].

Where the evidence ends

• No approval in men. The Vyleesi label states that it “is not indicated for the treatment of HSDD in postmenopausal women or in men” and that it is not indicated to enhance sexual performance [13].
• Blood pressure. With 1.75 mg subcutaneous, systolic pressure rose by up to 6 mmHg and diastolic by up to 3 mmHg, peaking at 2 to 4 hours, with a heart rate reduction of up to 5 bpm. Values generally returned to baseline within 12 hours. It is contraindicated in uncontrolled hypertension or known cardiovascular disease [13]. In an ambulatory monitoring study in 397 women, systolic increases were about 2.4 to 3.2 mmHg versus placebo and transient [11].
• Nausea. It was the most common adverse reaction in the phase 3 trials: 40% versus 1% with placebo. 13% needed an antiemetic and 8% left the study [13].
• Focal hyperpigmentation. Reported in 1% with up to 8 doses per month (face, gums, breasts). With daily dosing for 8 days it reached 38%, was more frequent in darker skin, and resolution was not always confirmed [13].
• Small, older data in men. The male trials are phase 1 to 2, from 2004 to 2008, mostly sponsor-run, with laboratory endpoints such as RigiScan [6][7][8]. The largest is under an expression of concern [9].

What this means for you

The signal in men is real and narrow: men with an inadequate response to the vascular pathway [7], and combination with a low dose of a PDE5 inhibitor [8]. The label’s safety profile is your starting point for any patient [13]. Screen blood pressure and cardiovascular history first, and warn about nausea and pigmentation.

Source matters as much as dose. Bremelanotide from a licensed 503A pharmacy on a patient-specific prescription is a different product from vials labeled “PT-141 peptide” for research use only, which FDA named in warning letters in August 2026, as our status page records. If you prescribe through a hormone therapy program, document why the patient needs a compounded preparation. For another peptide with a central effect on sexual behavior, see kisspeptin.

References

1. Molinoff PB, et al. PT-141: a melanocortin agonist for the treatment of sexual dysfunction. Ann N Y Acad Sci. 2003;994:96-102. PMID 12851303. Link
2. Van der Ploeg LH, et al. A role for the melanocortin 4 receptor in sexual function. Proc Natl Acad Sci U S A. 2002;99(17):11381-6. PMID 12172010. Link
3. Pfaus JG, et al. The neurobiology of bremelanotide for the treatment of hypoactive sexual desire disorder in premenopausal women. CNS Spectr. 2022;27(3):281-289. PMID 33455598. Link
4. Wessells H, et al. Synthetic melanotropic peptide initiates erections in men with psychogenic erectile dysfunction: double-blind, placebo controlled crossover study. J Urol. 1998;160(2):389-93. PMID 9679884. Link
5. Wessells H, et al. Effect of an alpha-melanocyte stimulating hormone analog on penile erection and sexual desire in men with organic erectile dysfunction. Urology. 2000;56(4):641-6. PMID 11018622. Link
6. Diamond LE, et al. Double-blind, placebo-controlled evaluation of the safety, pharmacokinetic properties and pharmacodynamic effects of intranasal PT-141, a melanocortin receptor agonist, in healthy males and patients with mild-to-moderate erectile dysfunction. Int J Impot Res. 2004;16(1):51-9. PMID 14963471. Link
7. Rosen RC, et al. Evaluation of the safety, pharmacokinetics and pharmacodynamic effects of subcutaneously administered PT-141, a melanocortin receptor agonist, in healthy male subjects and in patients with an inadequate response to Viagra. Int J Impot Res. 2004;16(2):135-42. PMID 14999221. Link
8. Diamond LE, et al. Co-administration of low doses of intranasal PT-141, a melanocortin receptor agonist, and sildenafil to men with erectile dysfunction results in an enhanced erectile response. Urology. 2005;65(4):755-9. PMID 15833522. Link
9. Safarinejad MR, Hosseini SY. Salvage of sildenafil failures with bremelanotide: a randomized, double-blind, placebo controlled study. J Urol. 2008;179(3):1066-71. (Expression of concern, J Urol 2023.) PMID 18206919. Link
10. Safarinejad MR. Evaluation of the safety and efficacy of bremelanotide, a melanocortin receptor agonist, in female subjects with arousal disorder [retracted]. J Sex Med. 2008;5(4):887-897. PMID 18179455. Link
11. White WB, et al. Usefulness of ambulatory blood pressure monitoring to assess the melanocortin receptor agonist bremelanotide. J Hypertens. 2017;35(4):761-768. PMID 27977473. Link
12. Kingsberg SA, et al. Bremelanotide for the treatment of hypoactive sexual desire disorder: two randomized phase 3 trials. Obstet Gynecol. 2019;134(5):899-908. PMID 31599840. Link
13. DailyMed. Vyleesi (bremelanotide injection), for subcutaneous use, prescribing information (revised 3/2024). Link
14. Hellstrom WJ. Clinical applications of centrally acting agents in male sexual dysfunction. Int J Impot Res. 2008;20 Suppl 1:S17-23. PMID 18552830. Link

This is general information, not medical or legal advice. Rules vary by state and change. Confirm your own facts with counsel.