Peptide comparison
MT-2 vs PT-141
MT-2 and PT-141 are both research peptides. This side-by-side compares their mechanism, typical research dosing, half-life, routes and safety so you can see how they differ. For research use only.
| MT-2 | PT-141 | |
|---|---|---|
| Category | Aesthetic | Aesthetic |
| Overview | A synthetic, non-selective melanocortin receptor agonist studied for skin tanning and erectile dysfunction; never approved by any regulatory authority and associated with... | PT-141 (bremelanotide) is an FDA-approved melanocortin receptor agonist — marketed as Vyleesi — indicated for hypoactive sexual desire disorder (HSDD) in premenopausal... |
| How it works | MT-2 is a broad-spectrum melanocortin receptor agonist with significant activity at MC1R, MC3R, MC4R, and MC5R, and negligible binding at the adrenal MC2R (ACTH receptor). This non-selective profile accounts for its wide and partly unpredictable range of effects. At MC1R, expressed on cutaneous melanocytes, MT-2 activates adenylyl cyclase via Gs coupling, raising intracellular cAMP and driving protein kinase A (PKA) phosphorylation of CREB. This cascade upregulates tyrosinase and related enzymes responsible for eumelanin (dark brown/black pigment) synthesis, producing skin darkening at doses that do not require ultraviolet light exposure. The magnitude of tanning depends substantially on the individual's baseline skin phototype. At MC4R, expressed throughout the central nervous system, MT-2 modulates hypothalamic and limbic circuits that influence sexual arousal, appetite, and autonomic tone. MC4R activation increases oxytocin release and intersects with dopaminergic pathways, producing pro-erectile signalling in the spinal cord and brain that is independent of peripheral vascular mechanisms — a fundamentally different pathway from PDE-5 inhibitors such as sildenafil. This central mechanism also accounts for the appetite-suppressive and metabolic effects reported in animal models. MC3R and MC5R co-activation by MT-2 contributes to its side-effect profile (nausea, flushing, yawning, fatigue) and likely underlies some of the compound's autonomic and metabolic actions. The broad receptor footprint distinguishes MT-2 from bremelanotide (PT-141), which is structurally similar but pharmacokinetically different, and from afamelanotide (Scenesse), an MC1R-selective agonist approved for erythropoietic protoporphyria that does not share MT-2's erection-inducing properties. | Bremelanotide is a non-selective agonist at melanocortin receptors (MC1R, MC3R, MC4R, and MC5R; it does not bind MC2R). Its pro-sexual effects are attributed primarily to agonism at MC4R — and to a lesser extent MC3R — in hypothalamic and limbic nuclei, particularly the medial preoptic area and paraventricular nucleus. Activation of these receptors enhances dopaminergic and nitric oxide signaling within CNS circuits governing sexual motivation and arousal, a mechanism entirely distinct from the peripheral vasodilatory approach of PDE5 inhibitors (sildenafil, tadalafil). The compound therefore acts on desire and arousal at the level of the brain rather than on genital blood flow, which theoretically allows activity even when nitric oxide-dependent vascular pathways are impaired. MC1R agonism is present but lower than in MT-II, resulting in minimal tanning. Pharmacokinetics after SC injection: absolute bioavailability ≈ 100%; Tmax ≈ 1 hour; terminal half-life ≈ 2.7 hours (range 1.9–4.0 h); protein binding 21%; excretion predominantly renal (≈ 65%) with fecal component (≈ 23%). |
| Half-life | Not well characterised in humans. Animal and early human pharmacokinetic data suggest a short plasma half-life, typically cited at approximately 30 minutes to 1–2 hours for the parent peptide after subcutaneous injection. Biological effects (tanning, erection) outlast detectable plasma levels, indicating a pharmacokinetic–pharmacodynamic disconnect consistent with receptor-level downstream signalling persistence. Formal human PK studies are lacking. | Approximately 2.7 hours (range 1.9–4.0 hours) following subcutaneous administration. Peak plasma concentration is reached in approximately 1 hour. Blood pressure effects peak at 2–4 hours post-dose and return to baseline within approximately 12 hours. |
| Dosing reference | No approved or established clinical dosing protocol exists for MT-2; it is not an approved drug anywhere. Published human research studies administered doses of 0.01–0.03 mg/kg subcutaneously (the 1996 Dorr phase I study used 0.01–0.03 mg/kg in 3 healthy volunteers; the Wessells erectile-function crossover studies used 0.025 mg/kg). These were single-dose or short-course research administrations, not therapeutic regimens. No Phase III trials were conducted. These doses are provided as a research summary, not as clinical guidance. | The FDA-approved dose of Vyleesi (bremelanotide) is 1.75 mg administered as a single subcutaneous injection into the abdomen or thigh, at least 45 minutes before anticipated sexual activity. No more than one dose should be taken per 24 hours, and the manufacturer advises against using more than one dose per month on average (no more than eight doses per month) to reduce the risk of hyperpigmentation. Vyleesi is supplied as a single-use autoinjector. It should not be used in patients with uncontrolled hypertension or known cardiovascular disease due to transient blood-pressure effects. Earlier intranasal formulations (10–20 mg) were investigated in Phase 1–2 trials for male erectile dysfunction but the intranasal route was halted by the FDA in 2007 because of more pronounced blood-pressure concerns at those doses; the approved subcutaneous route at 1.75 mg produces more modest and manageable cardiovascular effects. |
| Routes | subcutaneous, intranasal | subcutaneous |
| Safety & side effects | MT-2 carries significant safety concerns and holds no regulatory approval in any jurisdiction. No large-scale or long-term human safety studies have been conducted. The following risks are documented in the published literature or represent substantiated regulatory concerns: Mole and melanoma risk: MT-2's direct stimulation of MC1R on melanocytes accelerates melanin production and has been associated with darkening of existing moles, development of new atypical (dysplastic) nevi, and — in published case reports — melanoma arising from pre-existing lesions during or shortly after use. A case involving a patient with familial atypical mole syndrome is documented in the peer-reviewed literature (PMC3663356). Anyone with a personal or family history of melanoma, or with many atypical moles, should be considered at substantially elevated risk. Regular dermatological screening, including ABCDE assessment of any new or changing moles, is strongly advisable if exposure has occurred. Dose-limiting side effects: Nausea is the most consistently reported and dose-limiting effect, occurring at doses as low as 0.01 mg/kg in some subjects; flushing, fatigue, and yawning are common. Spontaneous erections in men are not merely a benefit but an adverse event in non-therapeutic contexts. Serious adverse events in case reports: priapism requiring urological intervention, rhabdomyolysis, and renal infarction have each been described in case reports. Unregulated product quality: Research-grade material sold online is not pharmaceutical-grade, is not subject to GMP manufacturing controls, and may be impure, mislabeled, or contaminated. No consumer protection equivalent to drug-product standards applies. WADA prohibition: MT-2 is prohibited in competitive sport under the S2 class (Peptide Hormones, Growth Factors, Related Substances and Mimetics). Contraindications (based on mechanism and case data): use in individuals with personal or family history of melanoma, dysplastic nevi syndrome, current malignancy, or haematological disorders is particularly inadvisable. Pregnancy and breastfeeding use is unstudied and not recommended. | Bremelanotide (Vyleesi) is FDA-approved (June 2019) for HSDD in premenopausal women; this is the only approved indication. The most common adverse reactions in RECONNECT Phase 3 trials were nausea (40.0%), flushing (20.3%), headache (11.3%), and injection-site reactions. Nausea was severe enough for 13% of treated patients to use an antiemetic. VYLEESI transiently increases blood pressure and decreases heart rate after each dose; in trials, mean peak systolic blood pressure increased by up to 6 mmHg and mean peak diastolic by up to 3 mmHg, peaking at 2–4 hours and resolving within 12 hours. It is contraindicated in patients with uncontrolled hypertension or cardiovascular disease. Repeated use above eight doses per month may cause focal hyperpigmentation of the face, gums, and breasts, particularly in patients with darker skin tones. A single case of clinically apparent hepatotoxicity has been reported (possible, not established causal). Serious adverse events occurred in 1.1% of bremelanotide-treated patients versus 0.5% placebo in Phase 3. WADA status: bremelanotide is not explicitly named on the 2025 WADA Prohibited List as a specific compound, but WADA Section S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics) contains broad catch-all language that may encompass melanocortin receptor agonists; competitive athletes should seek guidance from their governing body or a qualified anti-doping advisor before use. Research-use material sold outside the pharmaceutical supply chain is unregulated; purity, identity, and sterility are not guaranteed. This information is for research reference only and is not a recommendation for human use outside a licensed medical context. |
For research use only. Not for human consumption. Always verify against current literature.