VIP (Vasoactive Intestinal Peptide): Inflammation, CIRS Protocols, and the Pulmonary Research
Vasoactive intestinal peptide (VIP) is one of those molecules that shows up in wildly different corners of the literature — gut physiology, lung medicine, immunology, and the contested world of chronic-illness "biotoxin" protocols. This research log entry tries to separate what is well-established biochemistry from what is preliminary, marketed, or outright unproven. As always, this is a reference note, not medical advice.
What VIP actually is
VIP is a 28-amino-acid neuropeptide, first isolated from porcine small intestine in 1970 by Sami Said and Viktor Mutt. Despite the "intestinal" name, it is distributed far more widely than the gut — it is found throughout the central and peripheral nervous system, the gastrointestinal tract, the lungs, the heart, and cells of the immune system. It belongs to the secretin/glucagon peptide family and signals through the VPAC1 and VPAC2 receptors.
Two properties drive most of the interest. First, VIP is a potent vasodilator and smooth-muscle relaxant — hence "vasoactive." Second, it has documented immunomodulatory and anti-inflammatory effects in preclinical models, where it can shift immune signaling away from pro-inflammatory patterns. Those are real, well-characterized pharmacological actions. The open question is whether delivering VIP as a drug translates those actions into meaningful clinical benefit in humans — and here the evidence gets thin fast.
VIP in the Shoemaker CIRS protocol
Much of the consumer-facing attention on VIP comes from its role in the Shoemaker protocol for Chronic Inflammatory Response Syndrome (CIRS) — a framework attributing multi-system symptoms to mold and biotoxin exposure. In that protocol, intranasal VIP nasal spray is positioned as the final step, used only after other elements (mold avoidance, binders, treatment of nasal MARCoNS colonization) have been addressed. The stated rationale is that premature VIP use may be ineffective or mask ongoing exposure.
Proponents report that intranasal VIP — a commonly cited regimen is 50 mcg four times daily for around 30 days — lowered inflammatory markers such as C4a and TGF-β1, improved quality-of-life scores, and normalized certain hormone levels in patients who had completed the prior steps.
The skeptical read matters here. CIRS itself is a controversial and not mainstream-validated diagnostic framework, and the VIP data supporting it are largely observational, drawn from case series and single-clinic experience rather than randomized, placebo-controlled trials. Improvements in surrogate markers like C4a and TGF-β1 are not the same as demonstrated clinical benefit, and there is no controlled evidence isolating VIP's effect from the rest of the protocol or from natural recovery. Intranasal VIP is not an FDA-approved therapy; it circulates through compounding pharmacies. Treat the enthusiastic dosing guides you'll find online as marketing-adjacent, not as settled science. See our FDA status reference for how compounded peptides sit relative to approved drugs.
Aviptadil: the pulmonary research and its disappointments
The most rigorous human data on VIP come not from CIRS but from pulmonary medicine, using aviptadil — a synthetic VIP, developed as RLF-100 and branded ZYESAMI. VIP is highly concentrated in the lung and had long-standing interest in acute lung injury and pulmonary hypertension, which made aviptadil a candidate when COVID-19 produced waves of severe respiratory failure.
The headline results were largely negative. In a randomized controlled trial of intravenous aviptadil in critical COVID-19 respiratory failure (Youssef et al., published in Critical Care Medicine in 2022), the primary endpoint — being alive and free of respiratory failure at day 60 — did not reach statistical significance when controlling for baseline ventilation status (odds ratio ~1.6, 95% CI 0.86–3.11, i.e., crossing 1). Investigators highlighted secondary signals such as improved 60-day survival and reduced IL-6, but those subgroup and secondary findings do not substitute for a met primary endpoint.
The larger, independent, NIH-sponsored trial was more decisive. TESICO (part of the ACTIV-3b program) enrolled 471 randomized participants, and its independent data and safety monitoring board recommended stopping the aviptadil arm for futility in May 2022. A well-powered, placebo-controlled trial stopped for futility is about as clear a negative signal as clinical research produces. Aviptadil has not received FDA approval for COVID-19, ARDS, or pulmonary hypertension.
More recent, smaller studies of inhaled aviptadil have reported more favorable numbers (for example, lower mortality versus placebo in one 2025 multicenter report). These are worth watching, but small single studies with promising point estimates are exactly the kind of result that has repeatedly failed to replicate at scale — and aviptadil's own track record is the cautionary tale.
The honest bottom line
VIP is genuinely interesting biochemistry: a well-defined 28-aa neuropeptide with real vasodilatory and immunomodulatory activity. But the gap between mechanism and proven benefit is wide. The pulmonary program — the best-funded, best-controlled test of the VIP hypothesis — largely failed its endpoints and was stopped for futility. The CIRS/intranasal use rests on uncontrolled, contested data within a framework mainstream medicine has not validated. If you're logging VIP research, file it under "biologically plausible, clinically unproven," and verify any newer claim against primary sources. For our structured entry, see /peptides/vip.
PepStash is a research log and reference tool. This article is educational and is not medical advice — it does not diagnose, treat, or recommend any protocol. Regulatory status and trial data change; always verify against primary sources and consult a licensed physician before making any decisions about your health.