Peforelin
A hormone borrowed from the sea lamprey, used to bring gilts and sows into heat, and what the trials actually found
Peforelin is the synthetic form of lamprey gonadotropin-releasing hormone III, a ten-amino-acid peptide first found in the brain of the sea lamprey. It was developed for pigs, as Maprelin, on the idea that it would release follicle-stimulating hormone more than luteinizing hormone and so help follicles grow after weaning. Large farm trials found only small effects on heat and none on litter size, and later hormone studies did not confirm the selective FSH release. It is a UK veterinary medicine for pigs. No study has given it to people.
No established human dose Details ↓
Recommended Dosing
No established human dose
No human dose exists for peforelin. It is authorised only as a veterinary medicine for pigs, and every study read here gave it to pigs, cattle, rats, mice or sea lampreys, or applied it to pituitary tissue and human cancer cells in the laboratory.
What is it?
Mammals have one main gonadotropin-releasing hormone, GnRH-I, which makes the pituitary release both luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The sea lamprey, a jawless fish, has others, and one of them, lamprey GnRH-III, differs from the mammalian hormone in the middle of the chain. Around 2000, researchers studying a possible separate 'FSH-releasing factor' in mammals reported that lamprey GnRH-III released FSH selectively from rat pituitary tissue and, in luteal-phase heifers, raised FSH without LH. That made it interesting for animal breeding, where more FSH means more follicles.
Peforelin is that peptide made synthetically, sold for pigs as Maprelin. The hope was that one injection after weaning, or after the hormone altrenogest is stopped in gilts, would replace equine chorionic gonadotropin (eCG) for stimulating follicles. A 2005 study in castrated male pigs found a clear rise in FSH without LH after 150 µg. But other groups did not reproduce the selectivity: in rats it released LH and FSH together and was 40 to 650 times weaker than GnRH; in cows it released LH, not FSH, at the highest dose; and in barrows and in estrus-synchronised gilts given the commercial product, it did not raise FSH at all.
The farm trials point the same way. In 1,850 animals across three herds, compared with eCG and saline, peforelin slightly raised the share of older sows in heat within a week of weaning and enlarged follicles in some groups, but did not change litter size, FSH or progesterone, and older sows had slightly more stillborn piglets. A 2017 follow-up of 212 animals found no improvement in litter performance over no treatment. One 400-sow farm study did report a better heat rate and some heavier piglets, mainly in late summer. In mice it has been tested as a replacement for eCG in superovulation, yielding fewer eggs but a high fertilisation rate.
Separately, cancer researchers noticed that lamprey GnRH-III has little hormonal effect in mammals but slows the growth of human breast, prostate and endometrial cancer cell lines in the laboratory, at micromolar concentrations. That made it a carrier for drug conjugates, which are different molecules and have their own literature. None of this has been tested in people.
Peforelin is authorised in the UK only as a veterinary medicine for pigs. It is not in the US Green Book's active-ingredient list, the EMA medicines list or Drugs@FDA. There is no human product, no human study and no human dose, and a veterinary injection is not a substitute for any human fertility medicine.
Mechanism of Action
Peforelin is a weak agonist of the mammalian GnRH receptor. Whether it also releases FSH selectively, through a receptor of its own, is the question its whole history turns on, and the studies disagree.
Selective FSH release: early reports
Released FSH but not LH from rat hemipituitaries, an effect blocked by inhibiting nitric oxide synthase (2002 study), and raised FSH without LH in luteal-phase heifers (2001 study).
Not selective: later studies
Released LH and FSH together through the ordinary GnRH receptor in rats, blocked by a GnRH antagonist (2002 study); released LH but not FSH in cattle (2004) and barrows (2010).
Direct effect on cancer cells
Bound receptors on human breast cancer cells and slowed their growth; swapping residue 6 or 7 for alanine removed the effect (2005 study).
Published Research
These studies were read from their PubMed abstracts on October 29, 2026: field trials in pigs, hormone studies in pigs, cattle, rats, mice and sea lampreys, laboratory work on pituitary tissue and human cancer cell lines, and one review. None was done in people. Amounts in the cards are veterinary or laboratory amounts, not human doses. Two records whose titles do not use one of its names are carded because their abstracts name it.
Field trial: 1,850 gilts and sows in three herds
Peforelin, eCG or saline was given after altrenogest (gilts) or after weaning (sows). Peforelin slightly raised the 7-day heat rate in older sows (95% against 91% and 90%) and gave the largest follicles in some groups, but older sows had more stillborn piglets, and litter size, FSH and progesterone did not differ.
Litter performance in 212 animals
Across three herds, peforelin did not change litter size or piglet mortality compared with eCG or saline. Live-born piglets of treated gilts were heavier than after eCG, but the authors concluded that peforelin did not improve litter performance over no treatment.
One high-producing 400-sow farm
Against no treatment, peforelin raised the heat rate (93.2% against 87.2%) and two farrowing indices, with no change in litter size or stillbirths. Piglet birth weight improved only in first-parity and older sows and in late summer.
Superovulation in mice
Given before hCG instead of PMSG (eCG) to young female mice at three concentrations, peforelin yielded significantly fewer eggs but a high fertilisation rate, with ovarian structure not significantly different.
Commercial product in estrus-synchronised gilts
In 24 gilts, 150 µg Maprelin XP10 did not raise FSH or LH, either before ovulation or at mid-cycle, while a GnRH-I agonist raised both. Most gilts in every group ovulated, and eCG produced the most ovulatory follicles.
Dose comparison in barrows
Six castrated male pigs received 0.1, 1.0 and 10 µg/kg into a vein in a Latin-square design. Only the highest amount raised LH, and none changed FSH; the authors call it a weak GnRH agonist.
FSH response in nine barrows
After 150 µg into the muscle, every barrow showed an FSH rise, about double baseline at 1 hour and raised for 10 hours, with no LH response; saline did nothing.
No selective FSH release in cattle
In bovine pituitary cells and in ovariectomised and cycling cows, it released LH and FSH together or LH alone, and only at the highest doses, while mammalian GnRH released both at every dose. The authors suggest it is a weak competitor at the mammalian receptor.
Selective FSH release in heifers
In the luteal phase, 0.25 and 0.5 mg infused into heifers raised FSH without LH, while mammalian LHRH raised only LH. On day 20 of the cycle, when progesterone was low, it released LH instead, suggesting that progesterone controls which hormone it releases.
No selective FSH release in rats
In rat pituitary cells and in intact and ovariectomised rats, it released both LH and FSH, with a binding affinity of 6.7 nM, and was 40 to 650 times weaker than LHRH. A GnRH receptor antagonist blocked both effects.
Rat pituitary tissue and nitric oxide
On cells carrying the mammalian GnRH receptor it was about 1,000 times weaker than GnRH, but on rat hemipituitaries it released FSH and not LH; blocking nitric oxide synthase stopped that, which the authors take as evidence for a separate FSH-releasing receptor.
The FSH-releasing factor hypothesis
An FSH-releasing fraction purified from sheep and rat hypothalamus lost its activity when treated with an antiserum to lamprey GnRH, supporting the idea that the mammalian factor is lamprey GnRH-III or something close to it.
In its own species: male sea lampreys
Injected into maturing male sea lampreys, it raised plasma oestradiol and progesterone, and four injections induced spermiation in 78% of animals by day 16, against none of the controls.
Structure and stability of the native peptide
The native peptide's direct antitumour activity on several cancer cell types was the starting point; disulfide-linked dimers proved more stable and more antiproliferative, with lower LH-releasing potency. The paper confirms the sequence Glp-His-Trp-Ser-His-Asp-Trp-Lys-Pro-Gly-NH2.
Human breast cancer cells
It is a weak pituitary agonist but slows the growth of human cancer cells at micromolar concentrations. A screen of designed analogues built only from natural amino acids found none more potent.
Which residues matter for anticancer activity
On MDA-MB-231 human breast cancer cells, replacing residue 6 or 7 with alanine removed both receptor binding and growth inhibition, and replacing histidine 5 kept binding but removed the effect on growth.
Prostate cancer cells and solution structure
Of 21 analogues tested on PC3 and LNCaP prostate cancer cells, acetylating lysine 8 or cyclising the chain increased growth inhibition. NMR showed the native peptide in an extended shape, unlike the folded turn of mammalian GnRH.
Review: a carrier for anticancer drugs
It is a weak GnRH agonist with little LH or FSH release in mammals but a direct antiproliferative effect on cancer cells, and has been modified by substitution, cyclisation, dimerisation and conjugation to polymers and chemotherapy drugs, with antitumour activity in cells and animals.
No Established Human Dose
No human dose exists for peforelin. It is authorised only as a veterinary medicine for pigs, and every study read here gave it to pigs, cattle, rats, mice or sea lampreys, or applied it to pituitary tissue and human cancer cells in the laboratory. No study giving it to a person was found, so the veterinary and laboratory amounts are not shown as doses.
What this rests on: PMID 23987986, PMID 16967433, PMID 23016589.
Educational information, not medical advice. The doses on this page come from approved labels, published studies and, where no study exists, amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
What a Buyer Needs to Know
What is sold, how it is mixed, stored and taken, and what is known about its safety, quality and legal status. Each part names its source. Where we have none, it says unknown.
What is sold
Unknown: no product of Peforelin is approved for people, and we hold no copy of a veterinary label or a published test that says what forms it is sold in (its approvals are under Legal status below). A vial's own label is a seller's claim, not a source.
Mixing a vial: a worked example
Unknown: no human dose of Peforelin has been established (see No Established Human Dose below), so there is no amount to work out. The reconstitution calculator does the arithmetic for any vial, water and dose.
Storage before and after mixing
Unknown: no label or published stability study on file says how to store Peforelin, before or after mixing. The mixing guide sets out the general rules, with their sources: keep a mixed vial in the fridge, and use it promptly, as the bacteriostatic water label says of any drug dissolved in it. The 28 days often quoted is the limit for an opened multiple-dose vial from a manufacturer, an outer limit set for sterility, not a time a mixed solution has been shown to keep. Nobody has published how long Peforelin stays intact once mixed.
How it is taken
Unknown: with no established human dose, there is no established way of taking Peforelin. What the human studies gave and how is set out under No Established Human Dose.
What to expect, and when
Unknown: no cited half-life and no label or trial duration on this page says how long Peforelin lasts or how long it was given. Results reported in the studies are under Published Research.
Side effects, and when to stop or get help
From the Side Effects section: Slightly more stillborn piglets in older sows than after eCG in one field trial (PMID 23987986); No reliable improvement in litter size or piglet survival (PMID 28405462); Fewer eggs than PMSG (eCG) when used for superovulation in mice (PMID 39409815). Full list and cautions ↓
When to stop or get help: unknown; no label or trial on file sets rules for stopping Peforelin. Treat a severe or unexpected reaction as a reason to stop and see a doctor.
Source: the Side Effects section below (“Reported in animals; no human safety data exist”).
Interactions
Unknown: a PubMed search for human interaction studies of Peforelin (reviewed 2026-10-28) found none. Unknown is not the same as safe to combine.
Every peptide's record, with its source: the interaction matrix.
Checking what you bought
Unknown: no published independent test of Peforelin products is in our lab-results database yet, so how products sold under this name measure up is not known.
To read a certificate of analysis, paste it into the COA decoder; it checks the measured mass against Peforelin's expected mass, 1,259.3 Da, from this entry's molecular data. Trust & Verification explains what independent testing can and cannot show.
Legal status
US: Veterinary Only (Approved only for animals). Sport: Prohibited in males, at all times (S2.2.1).
Country by country ↓ · Regulatory tracker
Source: this entry's approval status and the WADA Prohibited List, as in Legal Status below.
Side Effects & Contraindications
Reported Side Effects
Reported in animals; no human safety data exist.
Contraindications & Cautions
For people, the main point is that peforelin is not a human medicine.
Legal Status
Peforelin is a veterinary medicine for pigs in the UK; no human approval was found.
Frequently Asked Questions
?What is peforelin?
Synthetic lamprey gonadotropin-releasing hormone III, a ten-amino-acid peptide from the sea lamprey, used in pigs as Maprelin to stimulate follicle growth and heat.
?Does it release FSH selectively?
Early studies in rats, heifers and barrows said yes; later studies in rats, cows, barrows and gilts found it released LH, or both hormones, or neither, and acted as a weak GnRH agonist.
?Does it improve litters?
Not reliably. A 1,850-animal trial found small effects on heat and follicles but none on litter size, and a follow-up found no improvement over no treatment.
?Is it used in people?
No. It is a UK veterinary medicine for pigs. Its anticancer activity has been seen only in cancer cell lines.
References
- [other] PubChem CID 16197823, Peforelin: formula C59H74N18O14, molecular weight 1259.3. Read October 28, 2026. https://pubchem.ncbi.nlm.nih.gov/compound/16197823
- [other] UK Veterinary Medicines Directorate, Product Information Database, currently authorised products searched by active substance, read October 28, 2026: Maprelin 75 µg/ml solution for injection for pigs, VM 27569/4000, active substance peforelin, target species pigs. https://www.vmd.defra.gov.uk/ProductInformationDatabase/
- [pubmed] de Jong E, et al. "Effect of a GnRH analogue (Maprelin) on the reproductive performance of gilts and sows." Theriogenology, 2013;80(8):870-7. PMID: 23987986.
- [pubmed] de Jong E, et al. "Effect of a GnRH analogue (peforelin) on the litter performance of gilts and sows." Porcine Health Manag, 2017;3:6. PMID: 28405462.
- [pubmed] Vangroenweghe F, et al. "An evaluation of gonadotropin-releasing hormone analogue administered to gilts and sows on subsequent reproductive performance and piglet birth weight." Porcine Health Manag, 2016;2:1. PMID: 28405427.
- [pubmed] Amberger L, et al. "Evaluation of Synthetic GnRH-Analog Peforelin with Regard to Oocyte Differentiation and Follicular Development in C57BL/6J Mice." Animals (Basel), 2024;14(19). PMID: 39409815.
- [pubmed] Brüssow KP, et al. "Influence of synthetic lamprey GnRH-III on gonadotropin release and steroid hormone levels in gilts." Theriogenology, 2010;74(9):1570-8. PMID: 20708243.
- [pubmed] Barretero-Hernandez R, et al. "Lamprey GnRH-III releases luteinizing hormone but not follicle stimulating hormone in pigs." Reprod Domest Anim, 2010;45(6):983-7. PMID: 19497025.
- [pubmed] Kauffold J, et al. "Lamprey GnRH-III stimulates FSH secretion in barrows." Reprod Domest Anim, 2005;40(5):475-9. PMID: 16149955.
- [pubmed] Amstalden M, et al. "Evidence that lamprey GnRH-III does not release FSH selectively in cattle." Reproduction, 2004;127(1):35-43. PMID: 15056768.
- [pubmed] Dees WL, et al. "Lamprey gonadotropin-releasing hormone-III selectively releases follicle stimulating hormone in the bovine." Domest Anim Endocrinol, 2001;20(4):279-88. PMID: 11518621.
- [pubmed] Kovacs M, et al. "Lamprey gonadotropin hormone-releasing hormone-III has no selective follicle-stimulating hormone-releasing effect in rats." J Neuroendocrinol, 2002;14(8):647-55. PMID: 12153467.
- [pubmed] Yu WH, et al. "Lamprey GnRH-III acts on its putative receptor via nitric oxide to release follicle-stimulating hormone specifically." Exp Biol Med (Maywood), 2002;227(9):786-93. PMID: 12324658.
- [pubmed] Yu WH, et al. "The similarity of FSH-releasing factor to lamprey gonadotropin-releasing hormone III (l-GnRH-III)." Proc Soc Exp Biol Med, 2000;224(2):87-92. PMID: 10806415.
- [pubmed] Deragon KL, et al. "Effects of lamprey gonadotropin-releasing hormone-III on steroidogenesis and spermiation in male sea lampreys." Gen Comp Endocrinol, 1994;95(3):363-7. PMID: 7821772.
- [pubmed] Mezo G, et al. "Structure, enzymatic stability and antitumor activity of sea lamprey GnRH-III and its dimer derivatives." Peptides, 2007;28(4):806-20. PMID: 17254668.
- [pubmed] Herédi-Szabó K, et al. "Is lGnRH-III the most potent GnRH analog containing only natural amino acids that specifically inhibits the growth of human breast cancer cells?." J Pept Sci, 2006;12(11):714-20. PMID: 16967433.
- [pubmed] Herédi-Szabó K, et al. "Importance of the central region of lamprey gonadotropin-releasing hormone III in the inhibition of breast cancer cell growth." Peptides, 2005;26(3):419-22. PMID: 15652648.
- [pubmed] Pappa EV, et al. "Structure-activity studies of lGnRH-III through rational amino acid substitution and NMR conformational studies." Biopolymers, 2012;98(6):525-34. PMID: 23203758.
- [review] Manea M, et al. "lGnRH-III -- a promising candidate for anticancer drug development." Protein Pept Lett, 2013;20(4):439-49. PMID: 23016589.
- [other] US FDA, Drugs@FDA (openFDA): no application for peforelin. Read October 28, 2026.
Sources & Citations
Every study on this page was read from its PubMed record on October 29, 2026. Approval status comes from the UK Veterinary Medicines Directorate, the FDA Green Book, Drugs@FDA and the EMA medicines list, read October 28, 2026. Formula and weight are PubChem's. Grey Peptides sells nothing and links to no vendor.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.