VIP (Vasoactive Intestinal Peptide): The CIRS & Anti-Inflammatory Evidence Reviewed (2026)

Vasoactive intestinal peptide (VIP) is a 28-amino-acid signaling molecule your body makes naturally in the gut, lungs, brain, and immune cells. In peptide circles it is best known as the last step in the "Shoemaker Protocol" for mold-related illness, and as a lung-protective drug that was tested hard during the COVID-19 pandemic. This review separates what the laboratory and animal data actually show from what has been proven in humans, and it is blunt about where the evidence is thin.

What VIP Is

VIP belongs to a family of related peptides that includes secretin, glucagon, and PACAP (pituitary adenylate cyclase-activating polypeptide). It was first isolated from the small intestine in the 1970s, which is where the "intestinal" in its name comes from. Despite that name, VIP is found all over the body. Nerve fibers in the lungs, heart, gut, and brain release it, and immune cells in the gut lining produce it on their own.

VIP works by latching onto cell-surface receptors. The two main ones, called VPAC1 and VPAC2, are found on immune cells, blood vessels, smooth muscle, and lung tissue. A third receptor, PAC1, prefers the related peptide PACAP but also responds to VIP. When VIP binds these receptors, it raises a messenger molecule inside the cell called cyclic AMP (cAMP). That single switch sets off most of VIP's downstream effects.

One fact shapes everything about how VIP can be used as a drug: it does not last long. Once released into the blood, VIP is chewed up within roughly one to two minutes by enzymes including dipeptidyl peptidase-4 (DPP-4, the same enzyme some diabetes drugs block) and neutral endopeptidase. That short half-life is part of why VIP is delivered as a nasal spray, an inhaled mist, or a slow intravenous drip rather than a once-a-day pill or shot. You can read more about how delivery route changes a peptide's behavior in our nasal spray vs. injection bioavailability guide.

What VIP does naturally

Before it became a research drug, VIP was simply a normal part of body chemistry, and that everyday role is worth understanding. In the gut, VIP relaxes intestinal smooth muscle, increases water and electrolyte secretion, and helps control blood flow to the digestive tract. A rare tumor called a VIPoma overproduces VIP and causes severe watery diarrhea, which is the clearest real-world demonstration of how powerful the peptide's secretory effect can be. That same tumor syndrome is also a caution flag: more VIP is not automatically better.

VIP is also a key signal in the brain's master clock, the suprachiasmatic nucleus, where it helps keep the daily sleep-wake rhythm synchronized. And nerve fibers that release VIP run throughout the airways, where the peptide opens bronchial tubes and dilates lung vessels. So the same molecule touches digestion, sleep timing, breathing, blood pressure, and immune balance. That breadth is exactly why VIP is interesting as a drug, and also why it is hard to give it without causing effects somewhere you did not intend.

How VIP Works In The Body

VIP has two jobs that matter most for the way people use it today: it relaxes blood vessels and airways, and it calms the immune system.

Vasodilation and lung effects

VIP is one of the body's natural vasodilators. It relaxes the smooth muscle in blood vessel walls and in the airways, which widens them. In the lungs this lowers the pressure the heart has to push against and opens up the bronchial tubes. Researchers noticed years ago that people with primary pulmonary hypertension, a disease of dangerously high blood pressure in the lung arteries, appeared to have low VIP levels in their lung tissue and blood. That observation is what launched the idea of using VIP as a replacement drug.

Immune calming

This is the effect that drives most of the peptide-community interest. VIP acts directly on immune cells through the cAMP pathway. In the lab it tells macrophages and other front-line cells to make fewer inflammatory signals, such as TNF-alpha, IL-6, and nitric oxide, and to make more of the anti-inflammatory signals IL-10 and IL-1Ra. It also nudges the adaptive immune system away from a "Th1" pro-inflammatory pattern toward a "Th2" pattern, and it encourages the growth of regulatory T cells (Tregs), the cells that keep the immune system from attacking the body's own tissue (Gomariz 2005, review; Delgado 2013, review).

The mechanism goes a layer deeper than just "fewer inflammatory signals." By raising cyclic AMP inside immune cells, VIP interferes with NF-kB, a master switch that turns on dozens of inflammatory genes at once. Dialing down NF-kB is part of why VIP can shift a cell's whole behavior rather than blocking one pathway. VIP also acts on dendritic cells, the cells that decide whether the immune system attacks or tolerates something. Under VIP's influence, dendritic cells become more "tolerogenic," meaning they teach T cells to stand down. That is the link between the lab biology and the disease idea: if you can reliably push the immune system toward tolerance, you might be able to quiet an autoimmune attack.

In short, VIP behaves like a brake on inflammation. The catch, which runs through this whole review, is that most of this evidence comes from cells in a dish and from mice, not from large human trials. A clean mechanism in the lab is the starting point for a drug, not the finish line. The graveyard of failed anti-inflammatory therapies is full of molecules with beautiful cell-culture data that did nothing for patients.

The Evidence, Graded Honestly

VIP has been studied for very different uses, and the quality of evidence is wildly different across them. Here is the landscape at a glance.

Use	Best evidence available	Honest grade	Bottom line
Anti-inflammatory / immune mechanism	Cell and animal studies, multiple reviews	Strong (mechanism only)	Well established in the lab; not the same as proven in patients
Autoimmune arthritis	Mouse models (collagen-induced arthritis)	Moderate (preclinical)	Reproducible in mice; no completed human RCT
Pulmonary arterial hypertension	One small open study + a failed phase II	Weak / mixed	Early promise did not hold up in a controlled trial
COVID-19 respiratory failure	Large randomized controlled trial (TESICO)	Negative	Did not improve outcomes vs. placebo
CIRS / "mold illness"	One open-label trial of 20 patients	Very weak	No placebo control; not independently confirmed

Anti-inflammatory mechanism: strong in the lab

The basic biology is solid and has been reproduced across many laboratories. VIP lowers inflammatory mediators and raises anti-inflammatory ones in cultured immune cells, and it can blunt the body's response to bacterial toxin (lipopolysaccharide) in animals (Martinez 2004). This is real science. But "VIP calms inflammation in a dish" is a mechanism, not a treatment outcome. Mechanism alone has misled the field many times.

Autoimmune arthritis: convincing in mice, untested in people

The most cited disease work comes from arthritis models. In mice with collagen-induced arthritis (a stand-in for rheumatoid arthritis), VIP reduced joint inflammation and expanded CD4+CD25+ regulatory T cells, which is exactly what the mechanism predicts (Gonzalez-Rey 2006). The effect has been repeated by more than one group, and similar anti-inflammatory benefits have shown up in mouse models of inflammatory bowel disease and septic shock. That consistency across different disease models is genuinely encouraging, because it suggests the effect is real and not a fluke of one experiment.

It is also still a mouse. Mouse autoimmune models are notoriously generous; many drugs that cure arthritis in mice fail in human trials. No completed, published randomized human trial shows VIP treats rheumatoid arthritis, inflammatory bowel disease, or any other autoimmune condition. Some researchers have even argued the smarter path is not to inject VIP at all, but to use it in the lab to grow regulatory T cells that could then be given back to a patient, sidestepping the peptide's short half-life entirely. That idea remains experimental. The honest grade here is "promising preclinical," and promising preclinical is a long way from a treatment you can count on.

Pulmonary hypertension: early hope, then a miss

A small study in patients with primary pulmonary hypertension reported that inhaled VIP improved hemodynamic measures and was well tolerated, which generated real excitement (Petkov 2003). But that work was small and largely uncontrolled. When inhaled VIP (as the drug aviptadil) was later put through a randomized phase II trial in pulmonary arterial hypertension, the acute and three-month results were negative, and commercial development for that use stalled. This is a textbook example of why a promising open-label signal is not proof.

COVID-19: a clean answer, and it was no

During the pandemic, synthetic VIP (aviptadil, brand name ZYESAMI) was tested as a "lung-protective" rescue drug for the sickest COVID-19 patients. The rationale was sound on paper: VIP concentrates in a lung cell type (type II alveolar cells) that the virus attacks, and it has anti-inflammatory and vessel-protecting effects right where severe COVID-19 does its damage. The company-issued press releases were upbeat, emphasizing safety signals and survival anecdotes. But the large, NIH-supported randomized trial, called TESICO, gave a clear verdict: intravenous aviptadil did not significantly improve outcomes through day 90 compared with placebo, and serious adverse events were not lower in the aviptadil group (TESICO, Lancet Respir Med 2023). When a properly powered, placebo-controlled trial says no, that answer outweighs earlier hopeful reports and press releases. This episode is a useful lesson for reading peptide claims in general: a strong biological story plus a company's optimistic statements is not evidence. The randomized trial is.

CIRS / "mold illness": the weakest link

In the wellness world, VIP is most famous as the final step in Dr. Ritchie Shoemaker's protocol for Chronic Inflammatory Response Syndrome (CIRS), a controversial diagnosis tied to water-damaged buildings. The supporting human data is a single open-label trial of 20 patients who used 50 mcg of VIP nasal spray four times a day for at least 18 months. The authors reported improvements in inflammatory markers (TGF-beta1, C4a, VEGF, MMP-9), exercise pulmonary artery pressure, and quality of life, with good tolerability.

Be clear about what that study is and is not. It was open-label, with no placebo group and no blinding, run by the people who developed the protocol. With 20 self-selected patients and no control arm, you cannot separate a true drug effect from placebo, natural recovery, or the other steps of the protocol that came first. CIRS itself is not a diagnosis recognized in mainstream pulmonology or infectious disease. The biology of VIP is interesting; the human CIRS evidence is, frankly, not enough to call this proven. Treat strong online claims with skepticism, and lean on the peptide therapy safety checklist before acting on any of them.

How VIP Is Used

Because VIP is destroyed so fast in the bloodstream, route of delivery is everything.

Form	How it is given	Typical setting	Notes
Nasal spray	Sprayed into the nose, several times daily	Compounding-pharmacy / clinic CIRS protocols	The form behind the Shoemaker data; 50 mcg per spray was used in the trial
Inhaled (nebulized)	Breathed into the lungs	Pulmonary hypertension research	Targets lung vessels directly
Intravenous (aviptadil)	Slow infusion in a hospital	COVID-19 and critical-care trials	Hospital-only; continuous drip needed because of short half-life

A few practical points. The 50 mcg, four-times-daily nasal dose comes from one small study and should not be read as a validated, one-size-fits-all protocol. Many CIRS protocols only add VIP after other markers are corrected, which makes any single ingredient's effect impossible to isolate. And the injectable, hospital form (aviptadil) is a completely different product from a compounded nasal spray bought from a peptide vendor.

There is also a stability problem that does not get talked about enough. VIP is a fragile peptide. It degrades with heat, light, and time, and a nasal spray that has sat at room temperature or shipped without cold packs may contain far less active peptide than the label claims. With prescription drugs, a manufacturer guarantees potency and shelf life through stability testing. With compounded or research-use VIP, that guarantee usually does not exist. So even setting aside whether VIP works, there is a real chance a given product is partly or mostly inactive by the time it is used. That uncertainty makes self-experimentation especially unreliable, because a "no effect" result could mean the drug does nothing, or simply that the vial was dead on arrival.

VIP vs. Other Anti-Inflammatory Peptides

People researching VIP usually have an inflammatory or immune goal in mind, so it helps to see where it sits next to peptides that are easier to obtain and better characterized for healing or gut work.

Thymosin alpha-1 is an immune modulator with a much larger human evidence base, including approved use for some infections and cancers in other countries. If immune regulation is the goal, see our thymosin alpha-1 research review.
KPV, a tiny three-amino-acid fragment of the hormone alpha-MSH, is studied mostly for gut and skin inflammation and is far simpler than VIP. Our KPV peptide research review covers what is and is not known.
For gut-focused inflammation specifically, the field is broader than any one peptide; our peptides for gut health evidence guide compares the main options.

None of these is a proven cure for any disease either. The honest framing is that VIP has the most striking mechanism but, outside the hospital drug aviptadil, the thinnest human data of the group.

Safety And Side Effects

VIP's safety record in research settings is reassuring for short-term use, but it comes with real caveats.

The biggest known effect is also its main mechanism: vasodilation. VIP can lower blood pressure, cause flushing, and trigger headache or a fast heartbeat, especially at higher doses or by infusion. In the COVID-19 trial, the aviptadil group did not have fewer serious adverse events than placebo, which is a reminder that "natural to the body" does not mean "free of risk." In the small CIRS nasal-spray study, the drug was generally well tolerated, with one transient rise in the pancreatic enzyme lipase.

The larger issue for consumers is product quality, not just the molecule. Compounded or "research-use-only" VIP is not an FDA-approved medicine. Purity, sterility, and actual peptide content vary by source, and a contaminated nasal spray carries infection risk. Anyone considering VIP should treat sourcing as a safety question, not just a price question. Our peptide vendor quality standards guide explains what third-party testing should look like.

People who should be especially cautious or avoid VIP without specialist supervision include anyone with low blood pressure, significant heart disease, or active gastrointestinal disease, as well as pregnant or breastfeeding people, for whom there is no safety data.

Legal And Regulatory Status

This is where VIP gets complicated, and it changed recently.

VIP is not FDA-approved for general therapeutic use in the United States. Its synthetic twin, aviptadil, received Fast Track and orphan-drug designations during development but never won full approval for COVID-19 or pulmonary hypertension, and the COVID-19 emergency-use bid did not succeed after the negative trial.

For compounding, the picture tightened. In late 2023 the FDA moved a long list of peptide bulk substances into "Category 2" of its interim 503A list, the bucket for substances the agency believes raise significant safety concerns (citing immunogenicity, impurities, and limited human data) (FDA, Certain Bulk Drug Substances That May Present Significant Safety Risks). VIP-family peptides sit in this same regulatory storm that swept up BPC-157, TB-500, and others. The category placements have shifted since then as some nominations were withdrawn and the FDA scheduled advisory-committee review, so the status is genuinely in flux as of 2026. For the broader compounding picture, see our BPC-157 / TB-500 FDA 503A review. The practical takeaway: legal availability through a US compounding pharmacy is uncertain and can change, and "research-use-only" products are not legal medicines.

Who VIP Is Realistically For

Strip away the marketing and the picture is narrow. As a hospital drug (aviptadil), VIP is an investigational agent that has not proven itself in its biggest tested use. As a compounded nasal spray, it is an unapproved product whose main human support is one small, uncontrolled CIRS study.

VIP may be worth a careful conversation with a knowledgeable physician for someone already deep in a supervised CIRS or biotoxin-illness workup who understands the evidence is preliminary. It is not a sensible first-line choice for general "anti-inflammatory" or "anti-aging" goals, where better-studied options and basic lifestyle measures do more for less risk. And it is not something to self-source and self-administer based on social-media claims. The mechanism is fascinating. The proof, for most uses, simply is not there yet.

Frequently Asked Questions

Is VIP FDA-approved?

No. VIP is not FDA-approved for general therapeutic use. Its synthetic version, aviptadil, received Fast Track and orphan-drug designations during development but never received full FDA approval. Compounded VIP nasal sprays are not approved medicines, and many peptide products are sold "for research use only," which is not a legal route to treat any condition.

Does VIP actually treat mold illness or CIRS?

The honest answer is that it is unproven. The main human evidence is a single open-label trial of 20 patients with no placebo group, no blinding, and the protocol's own developers as authors. That design cannot rule out placebo effect or natural recovery. CIRS is also not a diagnosis recognized in mainstream medicine. The VIP biology is interesting, but the clinical proof for this use is weak.

Why does VIP have to be a nasal spray or infusion instead of a pill?

VIP is destroyed in the body within about one to two minutes by enzymes such as DPP-4 and neutral endopeptidase. A swallowed pill would be broken down before it could work. Nasal, inhaled, and intravenous routes are used to get the peptide into the body fast enough to have an effect, and intravenous aviptadil even requires a continuous drip.

Did VIP work for COVID-19?

No. The drug form of VIP, aviptadil, was heavily promoted during the pandemic, but the large NIH-supported TESICO randomized trial found it did not significantly improve outcomes through day 90 compared with placebo. This is a clear example of a properly controlled trial overturning earlier optimistic reports.

What are the side effects of VIP?

The main effects come from its job as a blood-vessel dilator: low blood pressure, flushing, headache, and a fast heartbeat, mostly at higher doses or by infusion. Short-term tolerability in research has been reasonable, but the COVID-19 trial showed no reduction in serious adverse events versus placebo. Quality and sterility of compounded products are a separate, real safety concern.

Disclaimer

This article is for educational purposes only and is not medical advice. VIP is not FDA-approved for general therapeutic use. Talk to a qualified healthcare provider before considering any peptide.