VIP

LL-37 is the only cathelicidin antimicrobial peptide humans make, a 37-amino-acid, positively charged, helical fragment cut from a precursor protein called hCAP-18. It is a frontline player in the innate immune system, part of the body's chemical defense against bacteria, viruses, and fungi. This is mainstream, heavily studied human biology, not a fringe research peptide, though LL-37 itself is not an approved drug.

Thymosin alpha-1 (sold as Zadaxin, generic name thymalfasin) is a 28-amino-acid peptide originally isolated from the thymus gland, the organ that trains your immune system. Unlike most peptides in this space, it is a real, approved drug in a number of countries, including China and Italy, mainly for chronic hepatitis B and as an immune booster, though it has never been approved by the FDA in the United States. It has one of the larger human evidence bases of any peptide here, with more than 30 trials and over 11,000 subjects.

KPV is a tiny tripeptide, just three amino acids (lysine, proline, valine), that forms the tail end of the natural hormone alpha-MSH. It is studied almost entirely as an anti-inflammatory agent, particularly for gut and skin inflammation. There are no registered human clinical trials proving its benefits in people; the evidence base is cell-culture and animal studies, so anything you read about it treating disease is preliminary.

Thymogen is the brand name for L-Glu-L-Trp (glutamyl-tryptophan, the dipeptide EW), an immune-modulating peptide isolated from the calf thymus extract Thymalin. It is the smallest active piece of that thymic complex and is studied for boosting T-cell activity and immune function. It has been used clinically in Russia since 1990 but has never been evaluated or approved by any Western regulator, and rigorous independent trials are lacking.

Larazotide is an 8-amino-acid oral peptide (GGVLVQPG) designed to tighten the junctions between gut lining cells, aimed at celiac disease. For years it was the furthest-along celiac drug in development and it gets talked about online as a 'leaky gut' or zonulin blocker. The honest story is short: one phase 2b trial found a modest symptom benefit at the lowest dose only, the phase 3 trial was stopped in 2022 when it could not show a clear effect, and the sponsor 9 Meters Biopharma filed for Chapter 7 liquidation in July 2023. It is not approved anywhere.

Thymulin is a tiny nine-amino-acid hormone made by the epithelial cells of the thymus, first described in the 1970s as facteur thymique serique (FTS). It only works when bound to one zinc atom, which makes it an oddly neat marker of zinc status. It plays a part in training T cells, and animal work suggests anti-inflammatory and pain-reducing effects. It is sold online for immune support and hair loss, but there are no modern human trials of giving it, and the hair claims rest on lab dishes and a sponsor-linked cosmetic study.