VIP is a 28-amino-acid peptide your body already makes. The name is shorthand for vasoactive intestinal peptide, and it was first isolated from intestinal tissue, which is where the "intestinal" comes from. It is not a niche research chemical in the biological sense. It is an endogenous signaling molecule found in nerves throughout the gut, lungs, and central nervous system, and it sits in the same structural family as secretin, glucagon, and PACAP.
What it does in the body
VIP works through G-protein-coupled receptors called VPAC1 and VPAC2 (it also binds the PAC1 receptor weakly). Activating these receptors raises intracellular cyclic AMP, and the downstream effects depend heavily on where the receptor sits. On vascular endothelium, VPAC1 triggers nitric-oxide-mediated vasodilation; in smooth muscle, VPAC2 relaxes the tissue through a separate route. Across the body that adds up to smooth-muscle relaxation, vasodilation, regulation of gastrointestinal motility, and modulation of hormone secretion and immune signaling. The receptor pharmacology has been worked out in detail in peer-reviewed studies (review in *Frontiers in Endocrinology* / NCBI).
The synthetic version: aviptadil
Most of the human drug research uses a synthetic copy of the natural peptide, sold under the names aviptadil, RLF-100, and ZYESAMI. Because VIP relaxes airway and pulmonary vessels and tamps down inflammation, it has been tested mainly in lung disease.
- Sarcoidosis. In a phase II study, inhaled aviptadil given to 20 patients with biopsy-proven pulmonary sarcoidosis over four weeks lowered TNF-alpha and shifted regulatory T-cell populations in lung lavage fluid, an immunoregulatory signal rather than a cure (Prasse et al., *Am J Respir Crit Care Med*, 2010).
- Pulmonary hypertension. Small studies of inhaled VIP reported reductions in pulmonary artery pressure, though the evidence base stayed early-stage.
- COVID-19 / ARDS. This is where aviptadil got the most attention, and the most cautionary tale. Its developer announced in 2021 that intravenous ZYESAMI met endpoints in a phase 2b/3 trial for critical COVID-19. The FDA was not persuaded: it declined Emergency Use Authorization in late 2021, citing insufficient data, and declined again for a subgroup in 2022 (FierceBiotech coverage). Separately, the large NIH-run ACTIV-3b/TESICO trial stopped its aviptadil arm for futility after the drug failed to beat placebo at interim analysis.
So the honest summary is mixed. VIP has clear, well-documented biology and some early human signals, but no approved drug came out of the high-profile COVID programs, and the strongest independent trial was negative.
Regulatory and quality notes
Aviptadil has held FDA orphan-drug and fast-track designations for several respiratory conditions, but as of this writing it is not an FDA-approved drug. Material sold as "VIP" peptide online is research-use-only and is not approved for human consumption. If you are looking at a vendor's product, the things that matter are basic chemistry questions a certificate of analysis should answer: is it actually VIP, at the stated purity, free of meaningful contaminants? VIP is a long peptide that degrades readily, so identity (mass spec) and purity (HPLC) on a recent third-party COA are the relevant checks. peptideone aggregates independent vendor and testing signals to help with exactly that comparison.
Nothing here is medical, dosing, or efficacy advice. It is a plain-language summary of public research.