VIP Preclinical

What It Is

Vasoactive Intestinal Peptide (VIP) is a 28-amino-acid neuropeptide in the secretin/glucagon/PACAP superfamily. It was first isolated and named in 1970 by Sami Said and Viktor Mutt from porcine small intestinal extract for its vasodilatory activity (Said & Mutt, Science 1970; PMID 5452969). Over the following decades it became clear that VIP is endogenously produced throughout the body — in enteric neurons, pancreatic islets, brain (particularly the suprachiasmatic nucleus), lung, heart, and immune cells — and is one of the most broadly pleiotropic neuropeptides in mammalian biology.

The synthetic form of VIP is known as aviptadil (research code RLF-100), developed originally by Mondobiotech and subsequently by Relief Therapeutics and NRx Pharmaceuticals. Aviptadil has been investigated in pulmonary arterial hypertension (inhaled formulation), COVID-19-related acute respiratory distress syndrome (IV formulation, the COVID-AIV / STOP-COVID trials), and sarcoidosis. None of these programs has produced an FDA-approved product; Phase 3 results in both the PAH and COVID ARDS indications were negative or equivocal.

In the non-FDA / peptide-community context, VIP is used almost exclusively through the intranasal route as the final step of the Shoemaker protocol for Chronic Inflammatory Response Syndrome (CIRS) — a controversial diagnostic framework developed by Dr. Ritchie Shoemaker for illness associated with biotoxin exposure from water-damaged buildings. In the Shoemaker framework, CIRS patients characteristically have low serum VIP, and intranasal VIP replacement after sequential correction of upstream abnormalities (cholestyramine/Welchol binding, MARCoNS eradication, osmolality correction) is proposed to normalize immune-inflammatory markers (TGF-β1, MMP-9, C4a). Published evidence is primarily from Shoemaker's own practice-based case series; independent RCT validation does not exist.

VIP's extremely short plasma half-life (~2 minutes IV) creates formulation and delivery challenges. Intranasal delivery via compounded spray bypasses first-pass considerations and is the community's dominant route. Aviptadil for systemic indications has typically been delivered by IV infusion or aerosol inhalation. Subcutaneous VIP is less commonly used in any protocol.

Mechanism of Action

• VPAC1 receptor activation — VPAC1 is expressed on immune cells (T lymphocytes, macrophages, dendritic cells), gut epithelium, lung parenchyma, and liver. Activation via Gs-cAMP-PKA signaling drives the immune-modulatory and GI-regulatory effects of VIP.
• VPAC2 receptor activation — VPAC2 is expressed in the central nervous system (dominant in the suprachiasmatic nucleus master clock), pancreatic β-cells, cardiac myocytes, pulmonary smooth muscle, and some immune subsets. VPAC2 dominates the central circadian, neuroprotective, and pulmonary-vasodilatory effects.
• PAC1 cross-reactivity — VIP has weaker activity at PAC1, the preferential PACAP receptor. Contributes to some neuroprotective effects but is not the dominant receptor for VIP-mediated signaling.
• Immune modulation (Th1/Th17 → Th2/Treg shift) — VIP reduces pro-inflammatory cytokine production (TNF-α, IL-6, IL-12) while supporting regulatory T-cell development and Th2 bias. This is the central immune claim — VIP is an endogenous "brake" on pro-inflammatory signaling in the immune repertoire (Delgado et al., Amino Acids 2013; PMID 23381544).
• Neuroprotection — VIP protects neurons from glutamate-excitotoxicity and oxidative stress in preclinical models; enhances neural stem-cell proliferation; modulates amyloid-β and tau biology in Alzheimer's models. Weaker clinical-translation record than mechanism suggests.
• Pulmonary effects — Potent bronchodilator and pulmonary vasodilator. Modulates pulmonary artery pressure, stimulates surfactant production by type II alveolar pneumocytes. VIP deficiency has been documented in pulmonary arterial hypertension (Petkov et al., JCI 2003; PMID 12727923).
• Circadian rhythm regulation — VIP is the primary neurotransmitter in the suprachiasmatic nucleus (SCN), synchronizing circadian oscillator neurons across the master clock. VIP signaling disruption produces sleep and hormonal dysregulation.
• Gastrointestinal regulation — Stimulates intestinal water and electrolyte secretion, relaxes smooth muscle, modulates enteric immune responses. Excess VIP (e.g., from VIPoma) causes the characteristic secretory-diarrhea (Verner-Morrison) syndrome.
• Surfactant production — VIP stimulates surfactant synthesis by alveolar type II cells; mechanism basis for the ARDS-treatment rationale.
• Extremely short plasma half-life — ~2 minutes IV. This is the single biggest formulation challenge for systemic VIP indications and the reason most community use is intranasal (avoiding systemic PK limitations).

What the Research Shows

• Discovery (Said & Mutt, 1970; PMID 5452969) — Foundational paper isolating VIP from porcine intestine and describing its vasodilatory and secretory activity.
• Pulmonary arterial hypertension — open-label (Petkov et al., JCI 2003; PMID 12727923) — Inhaled VIP reduced pulmonary artery pressure and improved hemodynamics in primary PAH patients. Basis for subsequent development program.
• PAH Phase 2 (Leuchte et al., 2008, Eur Respir J) — Small controlled PAH trials. Mixed results; improvements in some hemodynamic measures but did not translate to durable Phase 3 success.
• PAH program — discontinued — The inhaled VIP PAH program did not produce an approved product; competing approved PAH therapies (endothelin receptor antagonists, PDE5 inhibitors, prostacyclin analogs) captured the indication.
• COVID-19 ARDS — RLF-100 / aviptadil — Youssef et al., medRxiv 2020 brief report described IV aviptadil in COVID ARDS with signal for oxygenation improvement. Subsequent randomized COVID-AIV and ACTIV-3b / TESICO Phase 3 trials produced negative or equivocal results; FDA did not grant EUA.
• CIRS / mold illness — Shoemaker (Health 2013) — Shoemaker RC et al., Health 2013;5(3):396-401 described intranasal VIP correction of CIRS symptoms after completion of upstream Shoemaker protocol. Practice-based case series; not independent RCT.
• Sarcoidosis pilot — Inhaled VIP explored in small sarcoidosis cohorts with exploratory endpoints; not advanced to Phase 3.
• Delgado et al. 2013 (Amino Acids; PMID 23381544) — Comprehensive review of VIP's immune functions and preclinical therapeutic potential in autoimmune models (RA, IBD, MS).
• VIP in COVID inflammation — Preclinical and observational work establishing low VIP in COVID-related pulmonary inflammation, underlying the aviptadil ARDS hypothesis that was not validated in Phase 3.
• Autoimmune preclinical models — Animal models of RA, IBD, experimental autoimmune encephalomyelitis demonstrate VIP reduces disease severity. Clinical translation has been limited.
• VIPoma / Verner-Morrison syndrome — VIP-secreting pancreatic tumors produce characteristic WDHA syndrome (watery diarrhea, hypokalemia, achlorhydria). Provides "excess VIP" biology counterpoint to therapeutic-dose VIP framework.
• Biological plausibility vs clinical translation gap — VIP is one of the clearest examples in neuropeptide therapeutics of a compound with extensive basic-science rationale across many diseases (asthma, PAH, ARDS, autoimmune, Alzheimer's, CIRS, etc.) but a weak-to-negative clinical-translation record when tested in well-designed RCTs. The plausibility-to-evidence gap is itself instructive about how preclinical mechanism and clinical efficacy diverge.
• Asthma and airway reactivity — VIP in asthma was one of the earliest proposed clinical uses (Said 1991). Small clinical experience did not translate into a viable therapeutic given the short half-life and the success of competing asthma pharmacology.
• Alzheimer's / neurodegeneration — Preclinical neuroprotection work in APP/PS1 and other AD models shows VIP-analog variants (stearyl-norleucine-VIP / SNV, ADNP derivatives) protect against cognitive decline. No approved AD indication.
• Autoimmune disease models — Collagen-induced arthritis, experimental autoimmune encephalomyelitis, and trinitrobenzene sulfonic acid colitis models all show VIP reduces disease severity. Translation to human autoimmune therapeutics never delivered.
• COVID-era renewed interest — VIP's pulmonary biology (surfactant, bronchodilation, anti-inflammatory) seemed uniquely suited to COVID ARDS. The RLF-100 / aviptadil Phase 3 COVID program deployed at scale during 2020–2023 and produced negative or equivocal primary endpoints across multiple trials, ending the near-term pharmaceutical pathway.

Human Data

• PAH inhaled VIP — open-label and Phase 2 — Petkov 2003 (primary PAH), Leuchte 2008 (PAH). Positive early signals; did not translate into approved product.
• COVID ARDS aviptadil IV — COVID-AIV / STOP-COVID / ACTIV-3b — Multiple trials examining aviptadil in severe COVID respiratory failure. Negative or equivocal primary endpoints; FDA declined emergency use authorization.
• Shoemaker CIRS practice case series — Shoemaker RC, Health 2013 describing intranasal VIP correction of CIRS biomarkers (TGF-β1, MMP-9, C4a, MSH) and symptoms after completion of upstream protocol steps.
• VIPoma case literature — Extensive clinical literature on VIP-secreting neuroendocrine tumors and the WDHA syndrome.
• Sarcoidosis pilots — Small exploratory inhaled VIP cohorts.
• No FDA-approved VIP or aviptadil product — Neither the PAH nor COVID development programs produced an approved product.

Dosing from the Literature

Reconstitution & Storage

VIP for community use is almost always supplied as a compounded intranasal spray from a 503A or 503B compounding pharmacy, or as lyophilized research-grade powder.

• Intranasal technique — Standard nasal spray administration. Spray while inhaling gently; alternate nostrils. Do not exhale through nose immediately after.
• Short plasma half-life — IV VIP is cleared in minutes. Systemic administration requires continuous infusion, which is impractical outside hospital settings.
• Storage — Refrigerated. Protect from light. Discard if cloudy, discolored, or past beyond-use date.
• Identity / purity verification — Third-party HPLC + mass spec for research-chemical powder. 503A/503B pharmacy products carry USP beyond-use-dating and compounder QC.

→ Use the Kalios Peptide Calculator for research-context dosing math

Side Effects & Risks

• Nasal congestion / runny nose (intranasal) — Most common. Usually transient.
• Diarrhea / loose stools — VIP stimulates intestinal secretion. Dose-dependent; can be dose-limiting at higher doses.
• Hypotension — VIP is a potent vasodilator. BP drops possible, especially with SubQ or IV routes. Caution in patients on antihypertensives.
• Flushing — Facial flushing and warmth from vasodilation. Usually mild.
• Headache — Possible, related to vasodilation effects on cerebral vessels.
• Tachycardia / palpitations — Reflex response to vasodilation.
• Injection-site reactions (SubQ) — Mild local erythema, tenderness.
• Drug interactions — Additive hypotension with antihypertensives, nitrates, PDE5 inhibitors. Caution with any vasoactive medication.
• Pregnancy / lactation — Not studied; avoid.
• Active malignancy — VIP receptors are expressed on many tumor types (VIPomas notwithstanding, VPAC1 is expressed on some adenocarcinomas). Theoretical concern; oncology supervision.
• Cardiovascular disease — Vasodilatory effects require caution in severe coronary artery disease, uncontrolled heart failure.
• WADA status — Not specifically named on the WADA Prohibited List. Athletes should consult their federation.

Bloodwork & Monitoring

• Serum VIP level — Normal range typically 23–63 pg/mL. CIRS patients in the Shoemaker framework often present well below the lower reference bound. Specialty lab assay.
• TGF-β1 — CIRS inflammatory marker; should trend downward with VIP treatment in the Shoemaker framework.
• MMP-9 — Elevated in CIRS; monitor response.
• C4a — Complement activation marker tracked in CIRS.
• MSH (α-MSH) — Often low in CIRS patients; may normalize with treatment.
• VEGF — Monitor alongside VIP in CIRS context.
• Blood pressure — Baseline and periodic; vasodilatory effects may require antihypertensive dose adjustment.
• CBC, CMP — Standard baseline.
• Hormonal panel (CIRS) — ADH, osmolality, MSH, ACTH, cortisol, testosterone as per Shoemaker workup.

Quick Compare — VIP vs KPV vs Thymosin α1 vs BPC-157

VIP is one of several community-used peptides targeting immune and inflammation biology. Clear comparison:

• VIP vs KPV — Both are community anti-inflammatory peptides. KPV operates via melanocortin biology (shorter acute half-life effect but orally bioavailable); VIP operates via VPAC receptors with broader pleiotropic effects but requires intranasal or IV delivery due to extreme half-life constraint.
• VIP vs Thymosin α1 — Thymosin α1 has approved pharmaceutical status for hepatitis; VIP has no approved indication despite Phase 3 investment. Different biology (adaptive immune polarization vs VPAC-cAMP signaling).
• VIP vs BPC-157 — Overlapping GI-healing claims. BPC-157 has a much more developed preclinical tissue-repair database; VIP's GI use is more inflammatory/immune-modulatory than structural-repair-focused.
• Best-fit for Shoemaker CIRS — VIP is the Shoemaker-framework final-step tool; the other peptides in this table are not part of the Shoemaker protocol.

→ See KPV profile  •  → See Thymosin α1 profile  •  → See BPC-157 profile

Supportive Nutrition & Adjuncts

The Shoemaker CIRS protocol involves much more than VIP alone. Nutritional and environmental foundations are higher-leverage and have better independent evidence than the VIP step.

• Environmental remediation (the largest lever) — In the CIRS framework, ongoing exposure to a water-damaged building nullifies every therapeutic intervention. Remediation or relocation is the foundational step and is not negotiable.
• Omega-3 (2–3 g EPA/DHA) — Systemic anti-inflammatory support; broad independent evidence.
• Vitamin D (target 40–60 ng/mL) — Standard immune and neurological support.
• Magnesium (300–400 mg) — Frequently depleted in chronic inflammation; cofactor for nitric oxide and vascular function.
• Glutathione support (NAC 600 mg + selenium 100–200 µg) — Antioxidant and detoxification support.
• Protein intake (1.2–1.6 g/kg) — Foundational for immune and neurological substrate availability.
• Sleep hygiene — Critical; VIP is also the master SCN signaling molecule, so sleep and circadian integrity are doubly relevant.
• Exercise (moderate, paced) — CIRS patients often require paced gradual re-conditioning. Anti-inflammatory and immune-supportive in moderate dose.
• Things to reduce — Ongoing water-damage exposure (primary), chronic alcohol, chronic sleep disruption, chronic stress without mitigation.

What to Expect — Timeline

VIP timeline expectations are drawn from Shoemaker-framework case series; independent RCT data is not available.

• Week 1 — Intranasal VIP is typically introduced only after the upstream protocol steps are completed. Initial dosing may produce mild nasal congestion and possible flushing.
• Week 2–4 — In Shoemaker's case series, subjective symptom improvement (energy, cognitive clarity, post-exertional tolerance) begins to be reported.
• Month 1–3 — TGF-β1, MMP-9, C4a inflammatory markers reported to trend toward normalization in the case series. Hormonal axis (ADH, osmolality, cortisol, testosterone) may show rebalancing.
• Month 3–12 (chronic use in Shoemaker framework) — Continued stabilization. VIP is often maintained long-term in the framework, though independent outcomes data is limited.
• Ongoing exposure — If biotoxin exposure continues (ongoing water damage, mold, unaddressed building), expect no sustained benefit. Environmental remediation is prerequisite.
• Non-responders — Real. CIRS as a diagnostic category is itself controversial in mainstream medicine; "non-response" may reflect misdiagnosis, non-Shoemaker pathophysiology, or ongoing exposure.
• If you feel worse — Persistent hypotension, new cardiovascular symptoms, severe diarrhea, worsening rather than improving symptoms. Cessation and evaluation.

Practical User Notes

• Follow the Shoemaker protocol sequence — VIP is the final step. Upstream steps (biotoxin binders, MARCoNS eradication, osmolality correction) are required before introducing VIP in the framework.
• Environmental remediation is primary — If exposure continues, no amount of VIP will produce sustained benefit in the CIRS framework.
• Work with a Shoemaker-trained clinician — The protocol is specific, staged, and requires laboratory surveillance. Not a self-administered regimen.
• Compounded intranasal supply — 503A / 503B pharmacy required. Research-chemical VIP powder is not the appropriate route for the Shoemaker protocol.
• Monitor BP — VIP is a vasodilator. Baseline and periodic BP; dose reduction may be needed if hypotension develops.
• Avoid concurrent vasoactive medications without oversight — Additive effect with nitrates, PDE5 inhibitors, and aggressive antihypertensives.
• Pregnancy / lactation — Avoid.
• Honest expectations — In the Shoemaker framework, VIP is the "final correction" step after upstream work. It does not substitute for the upstream steps, and its independent effect size is unknown.
• Red flags to stop — Persistent hypotension, severe diarrhea, severe headache, new cardiovascular symptoms, worsening rather than improving overall picture. Cessation and clinical evaluation.
• Mainstream medical perspective — CIRS as a diagnostic category is not endorsed by mainstream internal medicine / infectious disease / immunology. Patients pursuing the Shoemaker framework should be aware of this and maintain a relationship with a mainstream primary care physician for comprehensive differential diagnosis.

Commonly Stacked With

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Regulatory Status

Related Compounds

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Next Steps

Key References

1. Said SI, Mutt V. Polypeptide with broad biological activity: isolation from small intestine. Science. 1970;169(3951):1217-1218. PMID: 5452969.
2. Delgado M, Ganea D. Vasoactive intestinal peptide: a neuropeptide with pleiotropic immune functions. Amino Acids. 2013;45(1):25-39. PMID: 22139413.
3. Petkov V, Mosgoeller W, Ziesche R, Raderer M, Stiebellehner L, Vonbank K, et al. Vasoactive intestinal peptide as a new drug for treatment of primary pulmonary hypertension. J Clin Invest. 2003;111(9):1339-1346. PMID: 12727923.
4. Leuchte HH, Baezner C, Baumgartner RA, Bevec D, Bacher G, Neurohr C, Behr J. Inhalation of vasoactive intestinal peptide in pulmonary hypertension. Eur Respir J. 2008;32(5):1289-1294. PMID: 18579544.
5. Youssef JG, Said SI, Reichman JR, Alshaibi M. A Brief Report on RLF-100 (Aviptadil) in the Treatment of Critical COVID-19 Patients with Respiratory Failure. medRxiv. 2020. (Preprint basis for aviptadil COVID development program.)
6. Shoemaker RC, House DE, Ryan JC. Vasoactive intestinal polypeptide (VIP) corrects chronic inflammatory response syndrome (CIRS) acquired following exposure to water-damaged buildings. Health. 2013;5(3):396-401.
7. Said SI. Vasoactive Intestinal Polypeptide (VIP) in Asthma. Ann N Y Acad Sci. 1991;629:305-318. PMID: 1680332.
8. Delgado M, Pozo D, Ganea D. The significance of vasoactive intestinal peptide in immunomodulation. Pharmacol Rev. 2004;56(2):249-290. PMID: 15169929.
9. Dickson L, Finlayson K. VPAC and PAC receptors: From ligands to function. Pharmacol Ther. 2009;121(3):294-316. PMID: 19109992.
10. Harmar AJ, Fahrenkrug J, Gozes I, Laburthe M, May V, Pisegna JR, Vaudry D, Vaudry H, Waschek JA, Said SI. Pharmacology and functions of receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide: IUPHAR review 1. Br J Pharmacol. 2012;166(1):4-17. PMID: 22289055.
11. Verner JV, Morrison AB. Islet cell tumor and a syndrome of refractory watery diarrhea and hypokalemia. Am J Med. 1958;25(3):374-380.
12. Zhao H, Zhu H, Huang J, Zhu Y, Hong M, Zhu H, Zhang J, Li S, Yang L, Lian Y, Huang S. The synergy of vasoactive intestinal peptide and melatonin during anti-inflammation in collagen-induced arthritis rats. Mol Med Rep. 2018;17(5):6723-6732.
13. Gozes I, Furman S. Clinical endocrinology and metabolism. Potential clinical applications of vasoactive intestinal peptide: a selected update. Best Pract Res Clin Endocrinol Metab. 2004;18(4):623-640. PMID: 15533779.
14. ClinicalTrials.gov. Aviptadil (RLF-100) in the Treatment of Acute Respiratory Distress Syndrome Due to COVID-19 (COVID-AIV). Multiple NCT registrations. 2020–2024.
15. NIH / ACTIV-3b / TESICO trial publications on aviptadil in hospitalized COVID-19 with respiratory failure (Lancet Respir Med, 2023).