PEG-MGF

Insulin is a 51-amino-acid peptide hormone that regulates blood glucose. It is the foundational peptide therapeutic and a reference point for modern peptide drug design.

Bremelanotide, developed as PT-141, is a cyclic seven-residue analogue of α-melanocyte-stimulating hormone that activates melanocortin receptors, with its effect on sexual desire attributed to MC3 and MC4 signalling in the brain. The FDA approved it in 2019 as Vyleesi, an on-demand subcutaneous autoinjector for premenopausal women with acquired, generalised hypoactive sexual desire disorder. Nausea occurred in 40% of phase 3 participants, and a 2024 reanalysis found effect sizes from nil to small on most trial outcomes.

GHK-Cu is the copper(II) complex of glycyl-L-histidyl-L-lysine, a tripeptide found in human plasma at about 200 ng/mL at age 20 and 80 ng/mL by 60. It has a wide cell and animal literature on collagen synthesis, wound repair and anti-inflammatory signalling, a cosmetic market built on it, and — as a 2025 review notes — a surprising absence of clinical studies. Topical use is permitted as a cosmetic; it is not an approved drug.

MOTS-c is a 16-amino-acid peptide (MRWQEMGYIFYPRKLR; C101H152N28O22S2, ≈2,175 Da) encoded by a short open reading frame inside the mitochondrial 12S rRNA gene. Discovered in 2015, it promoted metabolic homeostasis and reduced obesity and insulin resistance in mice, and translocates to the nucleus under metabolic stress to regulate nuclear genes. Plasma levels decline with age. It is a research compound with no approval; its first phase 2 trial, in prediabetes, was recruiting in 2026.