Kisspeptin vs Enclomiphene: How They Differ
Kisspeptin is the body’s own peptide switch for the reproductive axis, acting on GnRH neurons to release LH and FSH, while enclomiphene is an oral small molecule, the trans-isomer of clomiphene, that raises the same hormones by blocking oestrogen’s braking signal. Both turn up the body’s own testosterone production instead of supplying testosterone from outside, which is why they get compared. They act at different points, have different human records and different regulatory histories. Here is what each is and what the studies found.
Findings
- Kisspeptin was identified in 2001 as the 54-amino-acid ligand of the receptor GPR54; kisspeptin-10 is the shortest form with full biological activity.
- In healthy men, kisspeptin-10 raised LH from 4.1 to 12.4 IU/L within 30 minutes, and a 22.5-hour infusion raised testosterone from 16.6 to 24.0 nmol/L and LH pulse frequency from 0.7 to 1.0 per hour (2011).
- Enclomiphene raised testosterone, LH and FSH while keeping sperm concentration in the normal range in two phase 3 trials in overweight men with secondary hypogonadism, where testosterone gel lowered sperm production (2016).
- Enclomiphene received a US FDA complete response letter in 2015 and a negative EU opinion in 2018; kisspeptin remains a research peptide in clinical studies.
What is kisspeptin?
Kisspeptin is encoded by the KISS1 gene. It was first isolated from human placenta in 2001 as a 54-amino-acid amidated peptide, the natural ligand of an orphan receptor now called GPR54 or KISS1R (Ohtaki et al., Nature, 2001). Kisspeptin stimulates gonadotropin-releasing hormone (GnRH) release directly through that receptor (Messager et al., Proc Natl Acad Sci USA, 2005), and people with mutations that inactivate kisspeptin signalling are infertile (Jayasena et al., J Clin Invest, 2014). Kisspeptin-10, the last ten amino acids of the chain, is the minimal sequence with full intrinsic activity (George et al., J Clin Endocrinol Metab, 2011).
The human hormone studies
The first human study infused kisspeptin-54 for 90 minutes in 6 men, in a double-blind crossover against saline. Mean LH rose to 10.8 IU/L against 4.2 on saline, FSH and testosterone rose too, and the peptide’s plasma half-life was 27.6 minutes (Dhillo et al., J Clin Endocrinol Metab, 2005).
Kisspeptin-10 was tested in men in 2011. A single intravenous bolus raised LH rapidly and in a dose-dependent way, from 4.1 to 12.4 IU/L at 30 minutes at the most effective dose (the highest dose gave a smaller response). A 22.5-hour infusion raised LH from 5.4 to 20.8 IU/L and testosterone from 16.6 to 24.0 nmol/L; a lower-rate infusion raised LH pulse frequency from 0.7 to 1.0 pulses an hour and more than tripled the size of each burst (George et al., J Clin Endocrinol Metab, 2011).
Fertility and sexual-function research
In 53 women undergoing IVF, a single injection of kisspeptin-54 triggered egg maturation; 92% went on to embryo transfer and 12 had clinical pregnancies (Jayasena et al., J Clin Invest, 2014). In 60 women at high risk of ovarian hyperstimulation, egg maturation occurred in 95% and none developed moderate, severe or critical hyperstimulation (Abbara et al., J Clin Endocrinol Metab, 2015).
Brain-imaging studies followed. In 29 healthy young men, kisspeptin enhanced limbic brain activity in response to sexual and couple-bonding images (Comninos et al., J Clin Invest, 2017). In 32 men with hypoactive sexual desire disorder, it modulated activity in the sexual-processing network and increased penile tumescence to sexual stimuli by up to 56% more than placebo (Mills et al., JAMA Netw Open, 2023), with a parallel trial in 32 women reporting changes in sexual and attraction brain processing (Thurston et al., JAMA Netw Open, 2022). Its place among libido peptides is covered in Peptides for Libido.
What is enclomiphene?
Clomiphene citrate, approved for ovulatory dysfunction in women, is a mixture of two isomers: zuclomiphene (cis) and enclomiphene (trans). Enclomiphene is a selective oestrogen receptor modulator, and the literature attributes most of clomiphene’s testosterone-raising effect in men to it (Earl and Kim, Expert Rev Endocrinol Metab, 2019). By blocking oestrogen’s negative feedback at the hypothalamus and pituitary, it lets LH and FSH rise, and the testes respond with more testosterone and continued sperm production.
The enclomiphene trials
A phase 2 trial in men with secondary hypogonadism compared oral enclomiphene with 1% testosterone gel. Enclomiphene raised morning testosterone to levels similar to the gel, raised LH and FSH, and conserved sperm counts (Wiehle et al., Fertil Steril, 2014). Two parallel phase 3 trials then enrolled overweight men aged 18 to 60 with low or low-normal testosterone and low or normal LH. After 16 weeks, testosterone rose in every group; LH and FSH rose on enclomiphene and fell on the gel, and enclomiphene kept sperm concentration in the normal range while the gel produced a marked fall in sperm production (Kim et al., BJU Int, 2016).
Regulators were not persuaded by the programme. The FDA issued a complete response letter in late 2015, asking for further phase 3 work, and in January 2018 the European Medicines Agency’s committee recommended refusing the application. Enclomiphene is covered here as a drug candidate with a substantial trial record, not as an approved medicine; its parent compound is compared with HCG in HCG vs Clomid.
How do kisspeptin and enclomiphene compare side by side?
| Question | Kisspeptin | Enclomiphene |
|---|---|---|
| What is it? | Endogenous neuropeptide (KISS1 gene) | Trans-isomer of clomiphene, a SERM |
| Size | Kisspeptin-10: 10 amino acids; kisspeptin-54: 54 | Small non-peptide molecule |
| Where it acts | KISS1R on GnRH neurons | Oestrogen receptors in hypothalamus and pituitary |
| Main research area | LH pulses, IVF egg maturation, sexual brain processing | Secondary hypogonadism with fertility preserved |
| Human evidence | Physiology studies and phase 2 IVF trials | Phase 2 and phase 3 trials |
| Regulatory status | Research compound | Not approved (FDA 2015, EMA 2018) |
| Forms we supply | 10 mg vial and ready-mixed nasal spray | Not supplied |
Which fits which research question?
- GnRH and LH pulse generation: kisspeptin, which acts at the top of the axis and whose human studies measured pulse frequency and size directly.
- Oestrogen feedback in men: enclomiphene, which works by removing that feedback.
- Behaviour and brain processing: kisspeptin, the only one of the two with human imaging and sexual-function trials.
No study comparing the two directly was found. Kisspeptin is compared with other compounds in Kisspeptin vs HCG and PT-141 vs Kisspeptin.
How is kisspeptin supplied?
Vistara Labs supplies kisspeptin-10 as a 10 mg lyophilised vial, reconstituted with bacteriostatic water, and as a ready-mixed Kisspeptin Nasal Spray delivering 0.175 mL per press. The human studies above used intravenous or subcutaneous administration. Certificates of analysis are on the lab reports page, buying details are in Buy Kisspeptin in Canada, and every order ships from within Canada. Vistara Labs does not supply enclomiphene.
Kisspeptin is supplied for laboratory research use only. The studies above were clinical research using pharmaceutical-grade preparations under medical supervision.
Frequently asked questions
What is the difference between kisspeptin and enclomiphene?
Kisspeptin is a neuropeptide that acts on the KISS1 receptor on GnRH neurons, starting the hormone cascade that releases LH and FSH. Enclomiphene is an oral non-peptide molecule that raises LH and FSH by blocking oestrogen’s negative feedback at the hypothalamus and pituitary.
Is enclomiphene approved?
No. The US FDA issued a complete response letter for enclomiphene in late 2015, and in January 2018 the European Medicines Agency’s committee recommended refusing its application. Its parent compound, clomiphene citrate, is an approved medicine for ovulatory dysfunction.
Does kisspeptin raise testosterone?
In human studies, yes. A 90-minute kisspeptin-54 infusion raised testosterone in 6 men, and a 22.5-hour kisspeptin-10 infusion raised it from 16.6 to 24.0 nmol/L, along with LH pulse frequency.
Can kisspeptin and enclomiphene be studied together?
No published human research on the combination was found. Both raise LH and FSH from above the testes, so in a single design their effects would overlap and be difficult to separate.
Where can I buy kisspeptin in Canada?
Vistara Labs supplies kisspeptin-10 as a 10 mg lyophilised vial and a ready-mixed nasal spray for laboratory research, shipped from within Canada by Canada Post Xpresspost.
Product details from vistaralabs.ca, October 2026. Sources: Ohtaki T et al. Metastasis suppressor gene KiSS-1 encodes peptide ligand of a G-protein-coupled receptor. Nature. 2001. PMID 11385580. Messager S et al. Kisspeptin directly stimulates gonadotropin-releasing hormone release via G protein-coupled receptor 54. Proc Natl Acad Sci USA. 2005. PMID 15665093. Dhillo WS et al. Kisspeptin-54 stimulates the hypothalamic-pituitary gonadal axis in human males. J Clin Endocrinol Metab. 2005. PMID 16174713. George JT et al. Kisspeptin-10 is a potent stimulator of LH and increases pulse frequency in men. J Clin Endocrinol Metab. 2011. PMID 21632807. Jayasena CN et al. Kisspeptin-54 triggers egg maturation in women undergoing in vitro fertilization. J Clin Invest. 2014. PMID 25036713. Abbara A et al. Efficacy of kisspeptin-54 to trigger oocyte maturation in women at high risk of ovarian hyperstimulation syndrome (OHSS) during in vitro fertilization (IVF) therapy. J Clin Endocrinol Metab. 2015. PMID 26192876. Comninos AN et al. Kisspeptin modulates sexual and emotional brain processing in humans. J Clin Invest. 2017. PMID 28112678. Mills EG et al. Effects of kisspeptin on sexual brain processing and penile tumescence in men with hypoactive sexual desire disorder: a randomized clinical trial. JAMA Netw Open. 2023. PMID 36735255. Thurston L et al. Effects of kisspeptin administration in women with hypoactive sexual desire disorder: a randomized clinical trial. JAMA Netw Open. 2022. PMID 36287566. Earl JA, Kim ED. Enclomiphene citrate: a treatment that maintains fertility in men with secondary hypogonadism. Expert Rev Endocrinol Metab. 2019. PMID 31063005. Wiehle RD et al. Enclomiphene citrate stimulates testosterone production while preventing oligospermia: a randomized phase II clinical trial comparing topical testosterone. Fertil Steril. 2014. PMID 25044085. Kim ED et al. Oral enclomiphene citrate raises testosterone and preserves sperm counts in obese hypogonadal men, unlike topical testosterone: restoration instead of replacement. BJU Int. 2016. PMID 26496621. European Medicines Agency, refusal of marketing authorisation for enclomifene (CHMP opinion, 25 January 2018). US FDA complete response letter for enclomiphene, December 2015, as reported by the sponsor.
More on this: Buy Kisspeptin in Canada: Vial and Nasal Spray.
All products supplied by Vistara Labs are intended for laboratory research use only. They are not drugs, are not approved for human or veterinary use, and are not intended to diagnose, treat, cure or prevent any condition. Nothing on this page constitutes medical advice or guidance for use in humans.
