Kisspeptin

Gonadorelin is a synthetic copy of natural GnRH (gonadotropin-releasing hormone), a 10-amino-acid peptide (pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) that tells the pituitary to release LH and FSH. It is FDA-approved for evaluating pituitary function and has historical use in inducing ovulation. In the peptide world it is mostly used off-label to keep the testes working during testosterone replacement, and the catch is that timing matters enormously: pulse it and you stimulate, give it continuously and you shut the system down.

Leuprolide (brand name Lupron) is a synthetic GnRH agonist, a modified peptide about 20 times more potent than natural GnRH, and it is FDA-approved for advanced prostate cancer, endometriosis, uterine fibroids, and central precocious puberty. The clever part is counterintuitive: it works by overstimulating the GnRH system so hard that the pituitary shuts down sex hormone production. It is a real, long-established prescription drug, not a research peptide, and it carries meaningful side effects from the low-hormone state it creates.

Octreotide is a synthetic eight-amino-acid mimic of the natural hormone somatostatin, the body's main 'off switch' for hormone secretion. It shuts down excess growth hormone, so it is a frontline FDA-approved drug for acromegaly, and it also tames the flushing and diarrhea of hormone-secreting carcinoid and other neuroendocrine tumors. This is real, approved medicine with decades of clinical data behind it, sold as Sandostatin (injectable, since 1988), Sandostatin LAR (monthly depot), and Mycapssa (oral capsule, approved 2020).

Lanreotide is an eight-amino-acid somatostatin analog, a close cousin of octreotide, given as a long-acting deep-injection gel (Somatuline Depot/Autogel) usually once a month. It is FDA-approved for acromegaly and for gastroenteropancreatic neuroendocrine tumors, and it carries an approval for carcinoid syndrome. It is established prescription medicine, not an experimental compound.

Pegvisomant (brand name Somavert) flips the usual acromegaly strategy on its head: instead of telling the tumor to make less growth hormone, it blocks growth hormone's receptor on target tissues directly. It is a PEGylated, genetically modified version of human growth hormone that acts as a receptor antagonist, FDA-approved in 2003 for acromegaly patients who do not respond well to surgery or other drugs. It is the single most effective option for normalizing IGF-1, which is why it is a key second-line therapy.

Macimorelin (brand name Macrilen) is an orally active ghrelin receptor agonist used as a diagnostic test, not a treatment. You drink a single dose, then doctors measure how much growth hormone the pituitary releases to diagnose adult growth hormone deficiency. It was FDA approved in December 2017 as the first oral diagnostic agent for that condition.