Peptide Research Library

The Peptide Research Library organizes 48 peptides and related compounds into four tiers based on the strength of available evidence and each compound's regulatory standing — not on popularity or marketing interest. Tier I contains FDA-approved compounds with large, replicated clinical evidence. Tier II includes compounds with real clinical data (often from Phase 1–3 trials) that are either still investigational or approved only in other countries or for a single narrow use. Lower tiers reflect compounds where human evidence remains thinner. The library notes explicitly that a compound's tier reflects how well established it is, not how interesting it is — and that many widely discussed compounds sit in lower tiers precisely because robust human data is still limited. This structure is intended to help readers calibrate what the science actually supports, rather than what is most promoted. Nothing in the library constitutes medical advice or a recommendation for use.

The library places five compounds in Tier I as FDA-approved with extensive clinical evidence. PT-141 (bremelanotide) is approved under the brand name Vyleesi for hypoactive sexual desire disorder (HSDD) in premenopausal women, functioning as a central melanocortin receptor (MC3R/MC4R) agonist. Tesamorelin is an approved GHRH analog indicated for HIV-associated lipodystrophy. Tirzepatide, a dual GIP/GLP-1 agonist marketed as Mounjaro and Zepbound, is approved and backed by one of the largest Phase 3 trial programs in metabolic medicine, though it carries a boxed warning for thyroid tumors. Oxytocin is FDA-approved as Pitocin for obstetric use, though its broader social and behavioral research is described as mixed and non-approved. Methylene blue, a small molecule rather than a peptide, is FDA-approved for methemoglobinemia; its use for cognitive purposes is off-label. Importantly, the library notes that research-grade material sold under these names is not the same as the approved medicine.

Tirzepatide is a dual agonist of the GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors. It is FDA-approved under the brand names Mounjaro and Zepbound and is supported by one of the largest Phase 3 clinical trial programs in the field of metabolic medicine. The library specifically flags that tirzepatide carries a boxed thyroid-tumor warning — the highest-level safety caution the FDA requires on a drug label. Readers seeking information about tirzepatide for their own health circumstances should consult a qualified healthcare professional, as this overview reflects general research information only and does not constitute medical advice.

Tier II contains 11 compounds described as having real clinical evidence — often from Phase 1 through Phase 3 trials — without full FDA approval. Among the most clinically advanced are: Retatrutide, an investigational triple GIP/GLP-1/glucagon agonist that achieved approximately 24% mean weight loss at 48 weeks in a Phase 2 obesity trial, with Phase 3 evidence now emerging, though it remains available only through trials. SS-31 received FDA accelerated approval in 2025 as Forzinity for the rare condition Barth syndrome and remains investigational for other indications. Thymosin Alpha-1 is approved in more than 30 countries as Zadaxin (though not in the US beyond orphan designations) and is described as the best-evidenced immune peptide in the library. Sermorelin, a GHRH analog, formerly held FDA approval as Geref before being discontinued, giving it a strong regulatory pedigree. These assessments reflect the state of published and regulatory evidence and should not be interpreted as endorsements or treatment recommendations.

Yes, the library identifies several Tier II compounds that hold regulatory approval outside the US but not from the FDA. Selank, a tuftsin-analog anxiolytic, is approved in Russia; the library notes its evidence is concentrated in a single research tradition. Semax, an ACTH(4-7)-analog nootropic, is similarly approved in Russia with evidence likewise concentrated in one research tradition. Thymosin Alpha-1 (Zadaxin) is approved in more than 30 countries for immune-related applications, though in the US it holds only orphan designations rather than full approval. The library presents this information to help readers understand the regulatory landscape globally, not to suggest these approvals confirm safety or efficacy for uses beyond the studied populations. Consulting a qualified healthcare professional is essential before drawing conclusions about any of these compounds.