Editorial note: this article summarises published research on GHK-Cu, Snap-8, Melanotan I and II, PT-141, hCG, Kisspeptin-10, Thymosin Alpha-1 and VIP. Baclabs does not sell these compounds or any peptide; we supply bacteriostatic water and reconstitution consumables. Nothing here is medical advice.
The term specialized peptides is a catch-all for compounds that do not fit the larger categories of weight-loss agonists, growth-hormone secretagogues or tissue-repair peptides. What unites them is that each acts on a specific receptor system or endocrine axis: copper-binding tripeptides that alter skin gene expression, melanocortin agonists that drive pigmentation and sexual arousal, gonadotropins and kisspeptin that steer the reproductive axis, and thymic or neuropeptide regulators of immune function.
This group also spans the full range of regulatory status. Some are licensed medicines with a Summary of Product Characteristics (SmPC) and decades of clinical use: human chorionic gonadotropin (hCG), bremelanotide, afamelanotide, oxytocin. Others are cosmetic ingredients with only manufacturer data (Snap-8), investigational research tools (Kisspeptin-10), or unlicensed products the MHRA has repeatedly acted against (Melanotan II). This pillar sets out what the evidence actually shows for each, where the UK stands legally, and how the reconstitution maths works for the ones supplied as lyophilised powder.
Four detailed articles sit under this page: GHK-Cu, Snap-8 and the “GLOW” blends; Melanotan I vs Melanotan II vs PT-141; hCG, Kisspeptin-10 and fertility protocols; and Thymosin Alpha-1, Thymalin, VIP and Oxytocin.
How specialized peptides are grouped
A useful way to read this cluster is by target system rather than by marketing claim.
| Group | Compounds | Primary target | UK status |
|---|---|---|---|
| Aesthetic / dermal | GHK-Cu, Snap-8, “GLOW”, “KLOW” | Skin gene expression; SNAP-25 mimicry | Cosmetic ingredients (topical); injectable use unlicensed |
| Melanocortins | Melanotan I (afamelanotide), Melanotan II, PT-141 (bremelanotide) | MC1R (pigment), MC3R/MC4R (arousal) | Scenesse licensed (EPP); Vyleesi FDA-licensed, not UK-licensed; Melanotan II unlicensed |
| Reproductive axis | hCG, Kisspeptin-10, follitropin alfa, triptorelin | LH receptor, GnRH neurones, FSH receptor, GnRH receptor | hCG, Gonal-F, triptorelin are POM; Kisspeptin-10 investigational |
| Immune / systemic | Thymosin Alpha-1, thymalin, VIP (aviptadil), oxytocin, glutathione | TLR signalling, thymic maturation, VPAC receptors, oxytocin receptor | Oxytocin POM; Tα1 licensed abroad, not UK; others unlicensed |
Aesthetic peptides: GHK-Cu and Snap-8
GHK-Cu is the copper complex of the tripeptide glycyl-L-histidyl-L-lysine. It occurs naturally in human plasma, and Pickart and Margolina report that plasma levels fall from roughly 200 ng/mL at age 20 to about 80 ng/mL at 60 [1]. The same review summarises gene-array work in which GHK altered the expression of around 31 per cent of human genes by 50 per cent or more, and cites a 12-week trial in 71 women in which a GHK-Cu facial cream increased skin density and thickness and reduced fine lines [1]. Most of the human data are for topical creams at cosmetic concentrations; the injectable use promoted online has no controlled human trials behind it.
Snap-8 (acetyl octapeptide-3) is an eight-amino-acid extension of argireline. Its manufacturer claims it competes with SNAP-25 in the SNARE complex that releases acetylcholine at the neuromuscular junction, softening expression lines. The supporting evidence is a single supplier study of 17 women using a 10 per cent solution of the commercial ingredient twice daily for 28 days, reporting a 34.98 per cent reduction in wrinkle depth against 27.05 per cent for argireline [2]. It is a topical cosmetic ingredient; there is no rationale, and no data, for injecting it.
“GLOW” and “KLOW” are not peptides. They are vendor names for blended vials, typically GHK-Cu, BPC-157 and TB-500 (GLOW), with KPV added in KLOW. No trial has tested these combinations. The GHK-Cu and Snap-8 article covers the hair-growth literature and the reconstitution of a 50 mg GHK-Cu vial.
Melanocortin agonists: Melanotan I, Melanotan II and PT-141
All three derive from alpha-melanocyte-stimulating hormone (α-MSH), but their receptor selectivity and regulatory histories differ sharply.
Melanotan I is afamelanotide, licensed as Scenesse. It is a 16 mg subcutaneous implant given every two months to adults with erythropoietic protoporphyria (EPP), a rare condition causing painful phototoxicity. In two controlled trials in 168 patients it increased pain-free light exposure and quality of life [3]. It is a prescription-only medicine administered in specialist centres; it is not a tanning product.
Melanotan II is a cyclic, non-selective analogue that hits MC1R (pigmentation), MC3R and MC4R (sexual arousal, appetite) and MC5R. It was studied in a small phase I pilot in the 1990s [4] and in a crossover study in men with psychogenic erectile dysfunction [5], then abandoned as a drug candidate. Reported effects include nausea, flushing, appetite loss, spontaneous erections in men, darkening of existing moles and new atypical naevi, and at least one reported melanoma [6]. Cancer Research UK states that it is illegal to sell or supply Melanotan injections in the UK, and the MHRA has described it as an unlicensed medicine that may not be safe [7]. In a 2024 Freedom of Information response the MHRA confirmed it has taken action to remove Melanotan products from the market for over ten years and received 16 Yellow Card reports for Melanotan II between 2012 and 2022 [8]. This site gives no dosing information for Melanotan II.
PT-141 is bremelanotide, the metabolite of Melanotan II lacking the pigmentation-driving activity at typical doses. It is FDA-licensed as Vyleesi for hypoactive sexual desire disorder (HSDD) in premenopausal women at 1.75 mg subcutaneously, no more than once in 24 hours and no more than eight doses a month [9]. It is not licensed in the UK. Earlier trials tested it in men with erectile dysfunction, including a randomised placebo-controlled study of bremelanotide in men who had failed sildenafil [10]. The melanocortin article compares all three and addresses the male-dosing question from the trial record.
Reproductive axis: hCG, Kisspeptin-10 and gonadotropins
hCG (human chorionic gonadotropin) is a glycoprotein that binds the LH receptor. Pregnyl 5,000 IU is licensed in the UK and Ireland for ovulation induction and luteal support in women, and for hypogonadotropic hypogonadism, delayed puberty and cryptorchidism in males; the SmPC lists 1,000–2,000 IU two to three times weekly for at least three months in hypogonadotropic men [11]. Ovitrelle is the recombinant equivalent (choriogonadotropin alfa 250 micrograms, roughly 6,500 IU) in a prefilled pen for triggering ovulation [12]. Both are prescription-only.
Kisspeptin-10 is the shortest active fragment of the KISS1 gene product, the peptide that sits upstream of gonadotropin-releasing hormone (GnRH). In healthy men, an intravenous bolus of 1 mcg/kg raised LH from 4.1 to 12.4 IU/L, and a 22.5-hour infusion at 4 mcg/kg/h raised testosterone from 16.6 to 24.0 nmol/L [13]. Jayasena and colleagues at Imperial College showed the response is sexually dimorphic: men and preovulatory women respond, follicular-phase women do not [14]. Kisspeptin-10 remains an investigational tool with no licensed product.
Follitropin alfa (Gonal-F) is recombinant FSH, licensed for anovulation, assisted reproduction and, in men with hypogonadotropic hypogonadism, at 150 IU three times weekly alongside hCG for at least four months [15]. Triptorelin (Gonapeptyl Depot 3.75 mg every 28 days) is a GnRH agonist that briefly stimulates and then suppresses the axis; it is licensed for prostate cancer, endometriosis, uterine fibroids and central precocious puberty [16]. Details, and the hCG reconstitution table, are in the fertility article.
Immune and systemic regulators
Thymosin Alpha-1 (thymalfasin, Zadaxin) is a 28-amino-acid thymic peptide acting as a TLR-2 and TLR-9 agonist. It is authorised in more than 35 countries for hepatitis B and C at a typical dose of 1.6 mg subcutaneously twice weekly, but has no UK or EU marketing authorisation [17]. The largest trial to date, TESTS, randomised 1,089 adults with sepsis to thymosin α1 or placebo every 12 hours for seven days and found 28-day mortality of 23.4 per cent versus 24.1 per cent, hazard ratio 0.97 [18].
Thymalin is a bovine thymic extract from the Russian bioregulator literature; a single-blind randomised trial in 80 older COVID-19 patients used 10 mg intramuscularly daily for 10 days [19]. VIP (vasoactive intestinal peptide, aviptadil) was tested in COVID-19 respiratory failure in the TESICO trial and did not improve 90-day outcomes [20]. Oxytocin is a prescription-only medicine for labour induction and postpartum haemorrhage; the SmPC dose is 5 IU by slow intravenous infusion after delivery [21]. Glutathione injections for skin lightening rest on a single flawed study and carry unquantified risk [22]. The immune regulators article covers each.
Reconstitution across this cluster
Several of these compounds are supplied as lyophilised powder. The formula is the same whatever the vial:
Concentration = vial content ÷ diluent volume. On a U-100 insulin syringe, 100 units = 1 mL, so each unit = concentration ÷ 100.
| Vial | Diluent added | Concentration | Per unit (U-100) | Per 10 units |
|---|---|---|---|---|
| hCG 5,000 IU | 1 mL | 5,000 IU/mL | 50 IU | 500 IU |
| hCG 5,000 IU | 2 mL | 2,500 IU/mL | 25 IU | 250 IU |
| hCG 5,000 IU | 5 mL | 1,000 IU/mL | 10 IU | 100 IU |
| GHK-Cu 50 mg | 2 mL | 25 mg/mL (25,000 mcg/mL) | 250 mcg | 2,500 mcg |
| GHK-Cu 50 mg | 5 mL | 10 mg/mL (10,000 mcg/mL) | 100 mcg | 1,000 mcg |
| Thymosin α1 5 mg | 2 mL | 2.5 mg/mL | 25 mcg | 250 mcg |
Two caveats. Licensed products come with their own solvent and instructions: the Pregnyl SmPC specifies reconstitution with the supplied solvent and immediate use [11], so drawing multiple doses from a vial over days is outside the licence. Second, any vial that will be 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; see bacteriostatic vs sterile water for the diluent decision and storage and the 28-day rule. Baclabs supplies UK-stocked bacteriostatic water in 30 mL vials; the reconstitution guide has the full worked method.
UK legal position
Under the Human Medicines Regulations 2012, products presented for a medicinal purpose require a marketing authorisation to be sold or supplied. hCG, Ovitrelle, Gonal-F, triptorelin, Scenesse and oxytocin are prescription-only medicines obtained through a prescriber. Bremelanotide and thymosin alpha-1 are licensed elsewhere but not in the UK, so any supply here is unlicensed. Melanotan II has never been licensed anywhere, and the MHRA’s position is that it should not be used [7][8]. Research-grade peptides sold “not for human consumption” sit outside the medicines framework only so long as they are not in fact supplied for human use; the purity and regulation article in Cluster 3 explains what a certificate of analysis does and does not tell you.
Frequently asked questions
What is the difference between Melanotan I and Melanotan II?
Melanotan I is afamelanotide, a linear α-MSH analogue selective for MC1R, licensed as the Scenesse implant for erythropoietic protoporphyria. Melanotan II is a cyclic analogue that also activates MC3R and MC4R, causing nausea, appetite suppression and spontaneous erections alongside tanning. It was never licensed and the MHRA has acted against its sale for over a decade [3][8].
Is PT-141 the same as bremelanotide?
Yes. PT-141 was the development code for bremelanotide, which the FDA licensed in 2019 as Vyleesi for hypoactive sexual desire disorder in premenopausal women. The licensed dose is 1.75 mg subcutaneously at least 45 minutes before anticipated activity, maximum eight doses a month. It has no UK marketing authorisation [9].
Does GHK-Cu work as an injection?
The human evidence for GHK-Cu is almost entirely topical: creams at cosmetic concentrations applied for 8–12 weeks in trials of 40–70 women [1]. There are no controlled human trials of subcutaneous GHK-Cu for skin or hair. Injectable GHK-Cu is unlicensed and its systemic effects, including on copper handling, have not been characterised in people.
Is hCG legal in the UK?
hCG (Pregnyl, Ovitrelle) is a prescription-only medicine with licensed indications in fertility treatment and male hypogonadotropic hypogonadism [11][12]. It is legal to possess when prescribed. Buying it from unregulated online sellers means receiving an unlicensed, possibly counterfeit product; the SmPC specifies refrigerated storage and immediate use after reconstitution, which such sellers rarely respect.
Which of these peptides have proper human trial data?
hCG, follitropin alfa, triptorelin, oxytocin, afamelanotide and bremelanotide are licensed medicines with phase 3 data and SmPCs. Thymosin alpha-1 has multiple randomised trials including the 1,089-patient TESTS trial [18]. Kisspeptin-10 has controlled physiology studies in healthy volunteers [13][14]. GHK-Cu, Snap-8, thymalin, VIP for COVID and glutathione injections have weak, small or negative human data, and the GLOW/KLOW blends have none.
References
- Regenerative and Protective Actions of the GHK-Cu Peptide in the Light of the New Gene Data. Pickart L, Margolina A. International Journal of Molecular Sciences, 2018
- Acetyl Octapeptide-3 (SNAP-8): ingredient summary and supplier study data. INCIDecoder, accessed 2026
- Afamelanotide. LiverTox, NCBI Bookshelf, NIH, 2024
- 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
- 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
- Pregnyl 5000 IU, powder and solvent for solution for injection: Summary of Product Characteristics. HPRA, 2018
- Ovitrelle 250 micrograms/0.5 ml prefilled pen: SmPC. emc, medicines.org.uk
- Kisspeptin-10 Is a Potent Stimulator of LH and Increases Pulse Frequency in Men. George JT et al. Journal of Clinical Endocrinology and Metabolism, 2011
- Effects of Kisspeptin-10 on Reproductive Hormone Release Show Sexual Dimorphism in Humans. Jayasena CN et al. Journal of Clinical Endocrinology and Metabolism, 2011
- GONAL-f (follitropin alfa): EPAR Product Information. European Medicines Agency
- Gonapeptyl Depot 3.75 mg: SmPC. emc, medicines.org.uk
- Thymosin alpha 1: A comprehensive review of the literature. Dominari A et al. World Journal of Virology, 2020
- The efficacy and safety of thymosin α1 for sepsis (TESTS): multicentre, double blinded, randomised, placebo controlled, phase 3 trial. Wu J et al. BMJ, 2025
- Peptide Drug Thymalin Regulates Immune Status in Severe COVID-19 Older Patients. Kuznik BI et al. Advances in Gerontology, 2021
- Intravenous aviptadil and remdesivir for treatment of COVID-19-associated hypoxaemic respiratory failure in the USA (TESICO): a randomised, placebo-controlled trial. Brown SM et al. Lancet Respiratory Medicine, 2023
- Oxytocin 10 IU/ml Solution for infusion: SmPC. emc, medicines.org.uk
- Glutathione for skin lightening: a regnant myth or evidence-based verity?. Sonthalia S et al. Dermatology Practical and Conceptual, 2018
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.