Endocrine & Reproductive Signaling

A natural brain hormone that acts as the upstream on-switch for the reproductive system; human studies show it reliably triggers reproductive hormone release, but it remains experimental.

Overview

Kisspeptin is a family of peptides made from the KISS1 gene. The longest natural form has 54 amino acids (kisspeptin-54); shorter forms such as kisspeptin-10 share the same active tail^[1,4]. It was first identified in 2001 as the natural partner of an orphan receptor now called KISS1R (GPR54)^[1]. In 2003, people with mutations in this receptor were found to never enter puberty, revealing kisspeptin as a gatekeeper of the reproductive axis^[2].

Human research, led largely by Imperial College London, shows that giving kisspeptin raises LH and, to a lesser degree, FSH and testosterone within hours^[4,5]. It has been tested as a gentler trigger for egg maturation in IVF^[7,8] and for effects on sexual and emotional brain processing^[9]. Repeated exposure can blunt the response^[6]. It is not an approved medicine.

Mechanism of Action

Kisspeptin binds KISS1R, a G protein-coupled receptor found on gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus^[1,2]. That triggers GnRH release, which tells the pituitary to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which in turn drive the ovaries and testes^[4]. Mice lacking the receptor have small testes or no follicle maturation, yet still respond normally to injected GnRH and gonadotropins, which places kisspeptin's action above GnRH^[2]. In women, the response depends heavily on cycle phase: LH rose far more in the preovulatory phase than in the early follicular phase^[5].

Kisspeptin-54 has a short life in the blood, with a measured plasma half-life of about 28 minutes in men^[4]. Continuous or repeated exposure can desensitize the system: in women with hypothalamic amenorrhea, the LH response shrank by about 90% after two weeks of twice-daily injections^[6]. Kisspeptin receptors also appear in limbic brain areas, which may explain effects on sexual and emotional brain processing seen on functional MRI^[9]. The gene was originally studied as a metastasis suppressor, and the peptide reduced cancer cell migration in early lab work^[1].

What the Research Shows

• Randomized crossover, men, 2005 (n=6, 90-minute infusion vs saline): mean LH 10.8 vs 4.2 U/L, FSH 3.9 vs 3.2 U/L, and testosterone 24.9 vs 21.7 nmol/L (all P<0.001), a roughly 15% acute testosterone rise^[4].
• Randomized crossover, women, 2007 (n=8 per cycle phase): LH rise over baseline was 0.12 IU/L in the follicular phase, 2.17 in the luteal phase (P<0.01) and 20.64 in the preovulatory phase (P<0.001)^[5].
• RCT, hypothalamic amenorrhea, 2009 (n=10, 2 weeks): the LH response fell from 24.0 IU/L on day 1 to 2.5 IU/L on day 14 (P<0.05), showing tachyphylaxis with repeated injections^[6].
• IVF trials, 2014 and 2015 (n=53 and n=60): a single kisspeptin-54 injection triggered egg maturation, with 23% clinical pregnancy per woman in the first study. In the second, in women at high risk of ovarian hyperstimulation syndrome (OHSS), maturation occurred in 95%, live birth was 45% per transfer, and no moderate or severe OHSS occurred. Neither study had a standard-care comparison arm^[7,8].
• Randomized crossover fMRI, men, 2017 (n=29): kisspeptin increased activity in limbic regions (cingulate, amygdala) when viewing sexual and bonding images and reduced negative mood (P=0.031); LH rose but testosterone did not change during the session^[9].

• Gpr54 knockout mice: isolated hypogonadotropic hypogonadism (small testes, absent follicle maturation) with normal hypothalamic GnRH content and normal responses to GnRH^[2].
• Mice, melanoma metastasis model: the peptide (then called metastin) reduced lung metastasis of receptor-expressing melanoma cells^[1].

• CHO cells expressing the receptor: kisspeptin reduced cell migration and invasion^[1].
• COS-7 cells with mutant GPR54: receptor variants from patients who failed to enter puberty showed sharply reduced signaling^[2].

Open Questions

• Whether kisspeptin improves IVF outcomes compared with standard triggers has not been tested in large head-to-head trials^[8].
• Whether any lasting benefit for low libido, low testosterone or fertility is possible given tachyphylaxis^[6].
• Nearly all human data come from one academic group; independent replication is limited^[4,5,9].
• Long-term safety of repeated use is unknown^[3].

Regulatory Status

Not approved by the FDA or any other major regulator for any use. Kisspeptin-10 has been on FDA's category 2 list of compounding bulk substances with significant safety risks since September 29, 2023, and it was not among the substances reviewed at the July 2026 Pharmacy Compounding Advisory Committee meeting^[3,10].

Related Compounds

A pregnancy hormone that acts like the body's LH signal, FDA-approved for specific fertility and testicular conditions, and explicitly labeled as not effective for weight loss.

Overview

Human chorionic gonadotropin (hCG) is the hormone the placenta makes in early pregnancy, and the one home pregnancy tests detect. Its effects in the body are virtually identical to luteinizing hormone (LH), the pituitary signal that tells the testes to make testosterone and the ovaries to release an egg and produce progesterone^[1,2]. Urine-derived hCG has been an FDA-approved drug since the 1970s, and a recombinant version (Ovidrel) was approved in 2000^[3,4].

Approved uses are narrow: undescended testes in boys, low testosterone caused by pituitary failure in men, and triggering ovulation in fertility treatment^[1,2,3]. The Pregnyl and Novarel labels both carry the same capitalized statement: hCG has not been demonstrated to be effective adjunctive therapy for obesity^[1,2]. A 1995 meta-analysis of the "hCG diet" trials reached the same conclusion^[6].

Mechanism of Action

hCG is a glycoprotein made of two subunits. In the recombinant form the alpha subunit has 92 amino acids and the beta subunit 145^[3]. The alpha subunit is essentially identical to the alpha subunits of LH, FSH and TSH; the beta subunit is what gives each hormone its identity^[1,2]. hCG binds the LH receptor, so in the testes it stimulates Leydig cells to make testosterone, and in the ovary it triggers final egg maturation and supports the corpus luteum, which makes progesterone^[1,2]. The Pregnyl label notes a small degree of FSH-like activity as well^[1].

Extra sugar chains on the beta subunit slow clearance. After an injection of recombinant hCG in healthy women, the mean terminal half-life was about 29 hours^[3], far longer than natural LH pulses. In men taking testosterone, which shuts down LH and FSH, hCG can stand in for LH at the testis: in one trial it kept testosterone inside the testes near normal levels^[7]. The labels state hCG has no known effect on fat mobilization, appetite, hunger or body fat distribution^[1].

What the Research Shows

• Meta-analysis, Br J Clin Pharmacol 1995 (controlled trials of the Simeons hCG diet): no evidence that hCG causes weight loss, redistributes fat, reduces hunger or improves well-being beyond the very low calorie diet itself^[6].
• RCT, JCEM 2005 (n=29 healthy men given testosterone, 3 weeks): testosterone suppressed LH and FSH to 5% and 3% of baseline. With placebo, intratesticular testosterone fell 94% (1234 to 72 nmol/L). hCG raised it in a dose-dependent way (P<0.001), from 25% below baseline at the lowest level tested to 26% above at the highest^[7].
• Registration trials of recombinant hCG (Ovidrel label) (3 randomized trials, about 290 women on the approved strength, each with a urine-derived hCG comparator): clinical pregnancy rates of 33% to 35% per initiated IVF cycle, and ovulation in 91.9% of women in an ovulation-induction trial^[3].
• Long clinical use: the cryptorchidism and male hypogonadism indications rest on decades-old approvals. The labels note that testicular descent produced by hCG in boys is usually temporary^[1,4].

• No animal findings are summarized here: the approved uses rest on human clinical experience and trials^[1,3].

Open Questions

• The testosterone-preservation trials measured hormone levels over weeks; long-term fertility outcomes in men on testosterone are much less studied^[7].
• Long-term effects of extended use outside approved indications have not been studied systematically.
• Products sold outside the regulated supply have unknown content and quality; only the licensed products on FDA's biologics list are approved^[4].
• Since 2020, hCG is regulated as a biologic, so compounded versions are no longer eligible for the usual compounding exemptions^[5].

Regulatory Status

FDA-approved prescription drug (Pregnyl, Novarel, generics; Ovidrel recombinant) that transitioned from drug to biologic licensing on March 23, 2020, which ended its eligibility for 503A/503B compounding exemptions^[4,5]. Labels state it is not effective for obesity^[1,2]. Prohibited in male athletes under WADA class S2^[8].

Related Compounds

A purified mix of FSH and LH-type activity extracted from the urine of postmenopausal women, FDA-approved to stimulate egg development during IVF.

Overview

Human menopausal gonadotropin (hMG), known generically as menotropins, is a fertility drug purified from the urine of postmenopausal women, whose pituitaries release large amounts of the two hormones that drive the ovaries^[1]. Each vial of the U.S. product, Menopur, carries 75 IU of follicle-stimulating hormone (FSH) activity and 75 IU of LH activity, with hCG supplying most of the LH activity^[1].

Its one FDA-approved use is helping women who ovulate develop several mature follicles during an assisted reproduction (IVF) cycle^[1]. Head-to-head trials and a regulator's meta-analysis found pregnancy and live birth rates similar to recombinant FSH^[1,4,5]. It is not approved in the U.S. for men or for any non-fertility purpose^[1].

Mechanism of Action

FSH binds receptors on the granulosa cells that line ovarian follicles, driving them to multiply and the follicle to grow. LH activity acts on the surrounding theca cells, which make the androgens that granulosa cells convert into estradiol^[1]. In Menopur, the LH activity comes mostly from hCG, which binds the same LH receptor; manufacturers may add urinary hCG from pregnant women to standardize total LH activity^[1]. Given over 7 to 20 days, this combination promotes growth and maturation of follicles in women whose ovaries still respond. A separate hCG injection is then used to trigger final egg maturation and ovulation^[1,6].

In multiple-dose studies, the FSH component had an elimination half-life of about 11 to 13 hours, similar whether given under the skin or into muscle^[1]. The practical difference from recombinant FSH shows up in the hormone profile: in one randomized trial, hMG produced fewer eggs but higher estradiol and lower progesterone at the end of stimulation^[5]. Whether the LH component meaningfully improves outcomes for most patients is still debated, since pooled pregnancy rates are broadly similar^[4].

What the Research Shows

• Pivotal RCT (Menopur label) (373 women randomized to menotropins in IVF or IVF/ICSI, Europe and Israel): continuing pregnancy 23% and clinical pregnancy 26%, non-inferior to recombinant FSH. OHSS occurred in 7.2%^[1].
• RCT, Human Reproduction 2008 (n=280, GnRH antagonist IVF/ICSI): ongoing pregnancy 35.0% with highly purified hMG vs 32.1% with recombinant FSH (P=0.61). Eggs retrieved were lower with hMG, 11.3 vs 14.4 (P=0.001)^[5].
• Regulator meta-analysis, Australian PBAC 2012 (6 RCTs vs follitropin alfa): ongoing pregnancy RR 1.12 (95% CI 0.98 to 1.28) and live birth RR 1.14 (0.98 to 1.34), both not significant, with no heterogeneity^[4].
• Integrated analysis of two RCTs (PBAC 2012) (986 IVF and 472 ICSI patients): in IVF, live birth was 26.5% with hMG vs 20.8% with recombinant FSH (OR 1.36, P=0.041). In ICSI there was no difference (18.8% vs 20.3%)^[4].

• No animal findings are summarized here: menotropins' approval and current use rest on human fertility trials^[1].

Open Questions

• Whether the LH component adds real benefit for most patients, versus specific subgroups, is unresolved^[4].
• Most comparative trials were sponsored by manufacturers and many were open-label or assessor-blind only^[1,4].
• Because it is urine-derived, batch-to-batch composition is less uniform than recombinant products; regulators have noted theoretical pathogen-transmission concerns, though none have been reported^[4].
• Since March 2020, menotropins are licensed as a biologic and are not eligible for compounding exemptions^[3].

Regulatory Status

FDA-approved as Menopur (originally NDA 021663, 2004) and deemed a biologic license on March 23, 2020, after which it no longer qualifies for 503A/503B compounding exemptions^[1,2,3]. Listed for IVF in Australia on a cost-minimization basis against recombinant FSH^[4]. Its LH and hCG content falls under WADA S2 restrictions for male athletes^[7].

Related Compounds

The body's own childbirth and bonding hormone, FDA-approved as an IV drug for labor and postpartum bleeding; nasal spray research for autism and social behavior has largely failed in large trials.

Overview

Oxytocin is a nine-amino-acid hormone made in the hypothalamus and released from the posterior pituitary. A synthetic version, Pitocin, is an FDA-approved hospital drug given intravenously to induce or strengthen labor when there is a medical reason, and to control bleeding after delivery^[1]. The label is explicit that it is not approved for elective induction, and it carries serious warnings because too much can overstimulate the uterus^[1].

Oxytocin's nickname, "the bonding hormone," comes largely from animal research on pair bonding in prairie voles^[2] and from a much-cited 2005 study suggesting a nasal spray increased trust^[4]. That early excitement has not held up well. The trust finding did not replicate reliably^[5], and the largest randomized trials of nasal oxytocin for autism found no benefit on their main outcomes^[6,7,8].

Mechanism of Action

Oxytocin acts on oxytocin receptors, which are dense in the uterine muscle. Binding raises calcium inside muscle cells and triggers contraction. Receptor numbers climb during pregnancy and peak in early labor at term, which is why the uterus becomes so responsive near delivery^[1]. At high levels, oxytocin also has built-in antidiuretic (water-retaining) and blood pressure effects, which explains the label's warning about water intoxication. In the bloodstream it is short-lived, with a half-life of about 1 to 6 minutes, cleared mainly by the kidneys and liver^[1].

In the brain, oxytocin and the related hormone vasopressin help process social cues. In prairie voles, partner preference forms when oxytocin and dopamine signaling are active together in reward areas^[2]. Whether nasal oxytocin reaches the human brain in meaningful amounts has long been debated. In rhesus monkeys, labeled oxytocin given by nose was detected in several brain regions, but only about 0.03% of the dose reached the striatum, and none was detected in spinal fluid; intravenous oxytocin produced no measurable labeled oxytocin in the brain^[3].

What the Research Shows

• FDA-approved clinical use: established for inducing or augmenting labor for medical reasons and for controlling postpartum bleeding, given intravenously in hospitals^[1].
• Trust experiment, Nature 2005: nasal oxytocin increased trust, an effect the authors linked specifically to accepting social rather than general risk^[4]. A 2015 critical review concluded this finding has not replicated well and that cumulative evidence does not robustly show oxytocin causes trust^[5].
• Autism RCT in children, NEJM 2021 (n=277 aged 3 to 16): nasal oxytocin showed no benefit over placebo^[6,8].
• Autism RCT in adult men, Japan, 2020 (n=106, 6 weeks): no difference from placebo on the primary measure of social reciprocity (effect size -0.08, P=0.69). Secondary measures of repetitive behavior and gaze improved modestly^[7].
• Autism RCT in young children, Australia, 2023 (n=87 aged 3 to 12, 12 weeks): no overall effect on caregiver-rated social responsiveness (P=0.686). A possible benefit in 3 to 5 year olds emerged in a subgroup analysis and needs confirmation. Adverse events were more common on placebo^[8].

• Prairie voles, pair bonding: oxytocin and vasopressin receptor signaling in brain reward areas, together with dopamine, supports partner preference formation^[2].
• Rhesus macaques, nasal delivery: labeled oxytocin reached orbitofrontal cortex, striatum, thalamus and brainstem along olfactory and trigeminal nerve routes, at low concentrations^[3].

Open Questions

• How much nasal oxytocin reaches the human brain, and whether that amount matters, is still unresolved^[3].
• Whether any subgroup, such as very young autistic children, truly benefits needs a dedicated trial^[8].
• Early positive findings on trust and social cognition may reflect small samples and publication bias^[5].
• Effects of long-term nasal use on the body's own oxytocin system are unknown.

Regulatory Status

FDA-approved prescription drug (Pitocin, NDA 018261) for medically indicated labor induction or augmentation and postpartum bleeding, for intravenous hospital use only in labor; the label states it is not indicated for elective induction^[1]. No nasal oxytocin product is FDA-approved for autism or any psychiatric use. Oxytocin is not named on the WADA 2026 Prohibited List^[9].

Related Compounds