VIP

VIP (Vasoactive Intestinal Peptide) is a 28-amino-acid neuropeptide widely distributed throughout the central and peripheral nervous systems, gastrointestinal tract, lungs, immune system, and other tissues. The peptide was first isolated from porcine small intestine in 1970 by Said and Mutt and characterized as a potent vasodilator. Subsequent decades of research have established VIP as a multifunctional neuropeptide and immunoregulator, acting on the VPAC1 and VPAC2 G protein-coupled receptors. The principal therapeutic interest is in VIP's anti-inflammatory and immunoregulatory effects. Phase 2 clinical research in sarcoidosis (Prasse 2010, inhaled VIP, 20 patients) demonstrated reduced TNF-alpha production and good tolerability. The most prominent contemporary off-label use is in chronic inflammatory response syndrome (CIRS) under the Shoemaker protocol, where intranasal VIP is the final step in a sequential treatment regimen. VIP is not FDA-approved for any indication. It is available only through 503A compounding pharmacies with a valid prescription.

Discovery and Basic Biology

VIP was first isolated and characterized by Sami Said and Viktor Mutt at the Karolinska Institute in 1970, published in Science. The discovery emerged from systematic characterization of small intestinal extracts for biologically active peptides. The compound was named for its origin (intestinal) and its initial characterized effect (vasoactive, producing vasodilation in multiple vascular beds).

Subsequent work established that VIP is not restricted to the gut despite its name. It is expressed widely throughout the body:

• Central nervous system (suprachiasmatic nucleus, amygdala, hypothalamus, cortex)
• Peripheral autonomic nervous system
• Enteric nervous system of the gut
• Lungs (parasympathetic innervation, smooth muscle)
• Heart (parasympathetic innervation)
• Immune cells (T cells, macrophages, dendritic cells)
• Reproductive organs

VIP functions in multiple modes: as a neurotransmitter at parasympathetic synapses, as a neuromodulator in the CNS, as an autocrine/paracrine factor on immune cells, and as an endocrine factor in certain pathological states.

The 28-amino-acid sequence is highly conserved across mammals. The peptide is part of the glucagon/secretin/VIP superfamily, structurally related to PACAP, glucagon, secretin, GIP, GHRH, and several other peptides.

Receptor Biology: VPAC1 and VPAC2

VIP acts on two principal receptors:

VPAC1 (VIP-pituitary adenylate cyclase activating peptide receptor 1):

• Broadly expressed in immune system, lungs, liver, gastrointestinal tract
• Predominant immune cell receptor
• Mediates most of VIP's anti-inflammatory effects
• Also responds to PACAP (lower affinity than VIP)

VPAC2:

• Predominantly expressed in CNS, smooth muscle, immune cells
• Mediates CNS effects including circadian rhythm modulation
• Responds to both VIP and PACAP

Both receptors are Gs-coupled GPCRs. Receptor activation triggers:

• Adenylyl cyclase activation
• cAMP elevation
• PKA activation
• Downstream phosphorylation cascades

A third related receptor, PAC1, responds predominantly to PACAP rather than VIP, but the receptor families overlap.

Anti-Inflammatory and Immunoregulatory Mechanisms

Substantial basic science evidence supports VIP's role as an endogenous anti-inflammatory and immunoregulatory neuropeptide. The principal mechanisms (from the Delgado, Gonzalez-Rey, and Ganea groups, among others):

• Reduced TNF-alpha, IL-1β, IL-6, IL-12 production by macrophages and dendritic cells
• Increased IL-10 production by macrophages, shifting toward anti-inflammatory phenotype
• Shift from Th1 to Th2 polarization of CD4+ T cell responses
• Induction of regulatory T cells (Tregs): Delgado 2005 showed VIP generates CD4+CD25+Foxp3+ Tregs in vivo
• Reduced NF-κB activation in inflammatory cells
• Inhibited dendritic cell maturation under inflammatory conditions
• Reduced expression of co-stimulatory molecules on antigen-presenting cells

These mechanisms are the basis for VIP's investigational role in autoimmune and chronic inflammatory diseases, including rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, sepsis, and sarcoidosis.

Sarcoidosis Phase 2 Study (Prasse 2010)

The principal clinical trial of VIP in a well-defined disease state was Prasse and colleagues' open-label Phase 2 study in sarcoidosis, published in American Journal of Respiratory and Critical Care Medicine in 2010:

• Design: open clinical Phase 2 study
• Population: 20 patients with histologically proven sarcoidosis and active disease
• Intervention: nebulized VIP for 4 weeks
• Findings:
  • VIP inhalation was safe and well-tolerated
  • Significantly reduced TNF-alpha production by cells isolated from bronchoalveolar lavage fluid
  • Increased Treg cells
  • No serious adverse events
  • Pulmonary delivery was practical and effective for the target tissue

The Prasse 2010 study is the best clinical evidence available for VIP's anti-inflammatory effects in a recognized chronic inflammatory disease. Despite the positive findings, VIP has not advanced to Phase 3 or FDA approval for sarcoidosis or any other indication.

Asthma Bronchodilation (Morice 1983)

Morice, Unwin, and Sever's 1983 Lancet paper demonstrated VIP's bronchodilator effects:

• VIP caused bronchodilation in asthmatic subjects
• Protected against histamine-induced bronchoconstriction
• Established the relevance of VIP's parasympathetic/bronchial smooth muscle effects

This work motivated investigation of VIP in asthma and COPD, though no FDA-approved respiratory VIP product has emerged.

The Shoemaker CIRS Protocol

The most prominent contemporary off-label use of VIP is in Chronic Inflammatory Response Syndrome (CIRS), particularly the variant associated with biotoxin exposure from water-damaged buildings (mold illness) or chronic Lyme disease. The principal proponent is Dr. Ritchie Shoemaker, whose protocol uses intranasal VIP as the final step in a sequential treatment regimen.

The CIRS framework, as developed by Shoemaker:

• CIRS is characterized by uncontrolled innate immune responses following biotoxin exposure
• Affected patients show deficiencies of regulatory neuropeptides MSH and VIP
• Multiple inflammatory markers are dysregulated: elevated MMP-9, TGF-β1, C4a, reduced VEGF, abnormal coagulation
• Pituitary axes (ACTH/cortisol, ADH/osmolality) become dysregulated
• A sequential protocol addresses each abnormality in order

The Shoemaker protocol sequential steps (simplified):

1. Removal from biotoxin exposure
2. Binder treatment (cholestyramine or welchol)
3. MARCoNS treatment with nasal antifungals/antibiotics
4. Various hormonal and inflammatory marker corrections
5. Intranasal VIP as the final step

VIP is positioned at the end because the prior steps must succeed for VIP to be useful (continuing biotoxin exposure or untreated MARCoNS makes VIP ineffective or counterproductive).

The Shoemaker 2013 paper in Health (SciRes) and the 2017 Internal Medicine Review paper reported:

• Symptom reduction in >90% of treated patients (uncontrolled physician reports)
• Normalization of MMP-9, TGF-β1, C4a
• Increased VEGF
• Normalization of clotting parameters and pituitary axes
• MRI grey matter volume restoration (2017 paper)

Evidence framing: the CIRS literature is largely from the Shoemaker group and associated practitioners. CIRS as a diagnostic entity is not universally recognized in mainstream medicine. The evidence base is principally uncontrolled clinical observation rather than randomized trials. Patients and clinicians considering VIP for CIRS contexts should understand the evidence quality and the controversy.

Chronic Lyme Application

VIP is also used off-label in chronic Lyme disease (or post-treatment Lyme disease syndrome). The rationale parallels the CIRS application: chronic Lyme is positioned as a chronic inflammatory state with neuropeptide deficiency, and VIP is positioned to restore regulatory neuropeptide signaling. The evidence base for this application is even thinner than for the mold-illness CIRS application.

503A Compounding Pharmacy Availability

VIP is available in the United States through 503A compounding pharmacies with a valid prescription. The principal formulation is intranasal spray (50 mcg per spray, 200-400 mcg per ml typical concentration). Some pharmacies prepare subcutaneous injection formulations. The 503A status depends on individual pharmacy interpretation of FDA bulk substance rules.

The compounding pathway is contested under FDA enforcement priorities. FDA has issued occasional enforcement actions against compounders selling peptides under contested 503A interpretations.

Regulatory Status

• FDA: Not approved for any indication. 503A compounding pharmacy availability with contested regulatory foundation.
• EMA: Not approved
• WADA: VIP is not currently on the WADA prohibited list. The peptide's anti-inflammatory effects do not clearly fit WADA's growth factor or peptide hormone categories.

VIP acts through its two GPCRs (VPAC1 and VPAC2) to produce a broad range of physiological effects spanning vascular, respiratory, gastrointestinal, immune, and central nervous system functions.

Receptor Signaling

Both VPAC1 and VPAC2 are Gs-coupled GPCRs that activate adenylyl cyclase upon VIP binding:

• VIP binds extracellular receptor domain
• Conformational change activates intracellular Gs subunit
• Gs activates adenylyl cyclase
• cAMP levels rise within target cell
• cAMP activates PKA
• PKA phosphorylates downstream substrates
• Effects vary by target cell type and PKA substrates

Vascular and Respiratory Effects

The original characterized VIP effects, mediated principally through smooth muscle VPAC1/VPAC2:

• Vasodilation: smooth muscle relaxation in arterial, venous, and capillary beds
• Bronchodilation: airway smooth muscle relaxation, established in asthma research
• Gastrointestinal smooth muscle relaxation: motility regulation
• Sphincter relaxation: lower esophageal, anal, urinary
• Reduced histamine-induced bronchoconstriction (Morice 1983)

Immune and Inflammatory Effects

The principal therapeutic interest centers on VIP's immunoregulatory effects, mediated through VPAC1 on immune cells:

Macrophages and dendritic cells:

• Reduced TNF-alpha, IL-1β, IL-6, IL-12 production
• Increased IL-10 production
• Inhibited dendritic cell maturation under inflammatory conditions
• Reduced expression of co-stimulatory molecules (CD80, CD86)
• Reduced antigen presentation in inflammatory contexts

T cells:

• Th1 → Th2 shift in CD4+ T cell polarization
• Induction of regulatory T cells (Tregs, CD4+CD25+Foxp3+) - Delgado 2005
• Reduced cytotoxic T cell activity
• Modulated Th17 responses

NF-κB pathway:

• VIP reduces NF-κB activation in inflammatory cells
• This is the central anti-inflammatory mechanism, downstream of multiple inflammatory stimuli

Central Nervous System Effects

VIP is densely expressed in specific CNS regions, particularly:

• Suprachiasmatic nucleus: VIP is a key neuropeptide for circadian rhythm generation
• Amygdala: involved in fear, emotion processing
• Cortex: cortical interneuron neurotransmitter
• Hypothalamus: pituitary regulation, autonomic function

CNS effects include modulation of circadian rhythm, sleep, mood, autonomic function, and pituitary axes. The Shoemaker 2017 MRI findings of grey matter volume restoration in CIRS patients on intranasal VIP suggest CNS effects relevant to clinical symptoms.

Pituitary-Adrenal Axis

VIP modulates hypothalamic-pituitary-adrenal (HPA) axis function:

• Direct effects on hypothalamic neurons
• Effects on pituitary corticotrope cells
• Indirect effects through other neuropeptides

This pituitary biology is the basis for VIP's role in restoring ACTH/cortisol and ADH/osmolality regulation in the Shoemaker CIRS framework.

Intranasal Delivery Pharmacokinetics

Intranasal delivery is the principal route in clinical use:

• Olfactory pathway: some direct access to brain via olfactory nerve
• Trigeminal nerve pathway: similar direct CNS access route
• Systemic absorption: portion of dose reaches systemic circulation
• Bypasses first-pass hepatic metabolism
• Half-life of intact peptide is short (minutes), but receptor-mediated effects persist longer

The CNS access via intranasal route is the rationale for the route choice in CIRS protocols, where central effects on grey matter and pituitary axes are clinically targeted.

Effects in clinical trial settings:

• Sarcoidosis (Prasse 2010, n=20, inhaled VIP 4 weeks): reduced bronchoalveolar TNF-alpha, increased Tregs, well-tolerated
• Asthma (Morice 1983): bronchodilation, protection against histamine-induced bronchoconstriction
• Various rheumatology and inflammatory bowel disease investigations: mostly preclinical, occasional small clinical studies

Effects in off-label CIRS use (Shoemaker protocol, uncontrolled clinical observation):

• Symptom reduction in >90% of treated patients per physician reports
• Normalization of inflammatory markers (MMP-9, TGF-β1, C4a)
• Increased VEGF
• Normalized coagulation parameters
• Improved pituitary axis function (ACTH/cortisol, ADH/osmolality)
• MRI grey matter volume restoration (Shoemaker 2017)
• Improved tolerance of brief biotoxin re-exposure
• Improved fatigue, cognitive function, sleep

Effects in off-label chronic Lyme use (limited reports, anecdotal):

• Variable response
• Best results when concurrent infection is treated first
• Anti-inflammatory and neuropeptide restoration framing

Effects in preclinical (animal and cell culture) models:

• Reduced arthritis severity (collagen-induced arthritis, multiple groups)
• Reduced experimental autoimmune encephalomyelitis (EAE, MS model)
• Reduced sepsis mortality (LPS endotoxic shock models)
• Reduced colitis severity (DSS colitis model)
• Bronchoprotection in asthma models
• Neuroprotection in stroke and TBI models

Honest evidence framing: VIP has substantial basic science evidence for anti-inflammatory and immunoregulatory effects. The Prasse 2010 sarcoidosis Phase 2 study is the strongest clinical trial evidence available. The CIRS evidence base is principally uncontrolled clinical observation from the Shoemaker group, in a diagnostic framework that is not universally recognized. The clinical research base is far smaller than mainstream peptides like semaglutide or even thymosin alpha-1. VIP is therapeutically interesting but undervalidated by modern clinical trial standards.

Important note: VIP has no FDA-approved dosing protocol. The doses described below come from clinical trials, the Shoemaker CIRS protocol, and compounding pharmacy practice.

Shoemaker CIRS intranasal protocol (the most widely used dosing schedule):

• Month 1: 50 mcg (1 spray) per nostril, 4 times daily (200 mcg total daily, alternating nostrils)
• Month 2 onward: may increase to 100 mcg (2 sprays) per nostril 4 times daily (400 mcg total)
• Duration: continuous use until clinical and biomarker improvement, often 12-18 months
• Prerequisites: complete earlier protocol steps first (biotoxin removal, binders, MARCoNS, hormone normalization)

Prasse 2010 sarcoidosis protocol:

• Nebulized VIP for pulmonary delivery
• 4-week duration
• Specific dose not consistently reported in public summaries

Subcutaneous off-label dosing (used in some research contexts):

• 100-250 mcg subcutaneously, 1-2 times daily
• Less common than intranasal
• Used for systemic anti-inflammatory effects when CNS targeting is not the primary goal

Routes:

• Intranasal: most common in CIRS context, bypasses first-pass metabolism, partial direct CNS access
• Inhaled (nebulized): for pulmonary targeting (Prasse 2010 sarcoidosis approach)
• Subcutaneous: systemic effect, less CNS access than intranasal
• Intravenous: not used in current off-label practice

Reconstitution and storage:

• Compounding pharmacies typically provide pre-reconstituted intranasal sprays
• For lyophilized peptide reconstitution: bacteriostatic water or 0.9% sodium chloride
• Refrigeration after reconstitution
• Typical stability: 4-8 weeks at 2-8°C
• Pharmacy quality varies

Cost and access considerations:

• VIP is among the more expensive compounded peptides (~$200-400 per month at typical CIRS dosing)
• Availability varies by state and pharmacy
• Insurance typically does not cover off-label peptide compounding
• Must be prescribed by a licensed physician

Special populations:

• Pregnancy and breastfeeding: avoid. Limited safety data
• Pediatric: limited use, avoid outside specialist care
• Active malignancy: theoretical caution due to angiogenesis effects (VIP is mildly angiogenic)
• Active infection: complete antimicrobial treatment first per Shoemaker framework
• Severe cardiovascular disease: theoretical caution due to vasodilatory effects

Adverse effects observed in Prasse 2010 sarcoidosis trial (inhaled VIP, 4 weeks):

• Generally well-tolerated
• No serious adverse events
• Minor cough and mild respiratory irritation (some patients)
• No significant cardiovascular events

Adverse effects in off-label intranasal CIRS use (Shoemaker reports and clinical practice):

• Nasal irritation, congestion, or mild burning (most common)
• Headache (occasional)
• Mild flushing (vasodilatory effect)
• Mild blood pressure decreases (occasional)
• Mild fatigue or sedation in some patients during initial use
• "Herxheimer-like" reactions: temporary symptom flare during initial treatment (in CIRS framework, attributed to immune system normalization revealing residual problems)
• Diarrhea (uncommon, possibly related to GI smooth muscle effects)

Theoretical concerns:

• Cardiovascular: VIP is a vasodilator. Theoretical hypotension risk, particularly with high doses or concurrent vasodilator medications
• Angiogenesis: VIP has mild angiogenic effects. Theoretical caution in active malignancy
• Asthma worsening (paradox): while VIP is bronchodilator, intranasal route in some patients with reactive airway disease has produced bronchospasm
• Immune modulation in unintended directions: in patients with autoimmune disease, immune-modulating effects could theoretically affect disease course in either direction
• Compounding pharmacy quality: lot-to-lot variability, identity verification depends on individual pharmacy practice

Pregnancy and breastfeeding: avoid.

Pediatric: avoid outside specialist care.

Athletes: VIP is not currently on the WADA prohibited list (as of 2026), but the regulatory environment for peptides is evolving. Athletes should verify current status before use.

Drug interactions:

• Vasodilators (nitrates, antihypertensives): additive hypotensive effect
• Phosphodiesterase inhibitors (sildenafil, tadalafil): theoretical additive vasodilation
• Immunosuppressants: theoretical additive immunomodulation
• Other anti-inflammatory peptides (e.g., thymosin alpha-1, BPC-157): theoretically additive but unclear clinical significance

Important Shoemaker protocol consideration: VIP should not be used before completing earlier protocol steps. Specifically:

• Ongoing biotoxin exposure must be removed
• MARCoNS must be treated
• VCS (Visual Contrast Sensitivity) test should pass
• ERMI mold testing should show acceptable levels
• Without these prerequisites, VIP is generally considered ineffective or potentially counterproductive

VIP sits in the immune-regulatory peptide category alongside other anti-inflammatory and immunomodulatory peptides. Its closest comparators:

• Thymosin Alpha-1: established immunomodulator with FDA-equivalent approvals in some countries. Different mechanism (Th1 enhancement vs VIP's broader immunoregulation). Often stacked with VIP in CIRS protocols.
• LL-37: cathelicidin antimicrobial peptide with immunomodulatory effects. Different mechanism. Sometimes used in CIRS contexts.
• KPV: α-MSH C-terminal tripeptide with anti-inflammatory effects. Different mechanism, smaller peptide. Used in some inflammatory conditions.
• BPC-157: synthetic gastric peptide with broad anti-inflammatory and tissue-repair effects. Different mechanism. Stackable with VIP for some inflammatory conditions.
• MSH (alpha-melanocyte stimulating hormone): the other regulatory neuropeptide highlighted in Shoemaker's CIRS framework. Not as widely available as VIP in research-chemical or compounding contexts.
• PACAP (pituitary adenylate cyclase-activating peptide): closely related peptide that also activates VPAC1 and VPAC2 (and PAC1). Less clinically used than VIP.

Common stacks circulating in CIRS and chronic inflammatory contexts:

• VIP + Thymosin Alpha-1: rationale of combining VIP's broad immunoregulation with Tα1's Th1 enhancement. Common in CIRS protocols for patients with both inflammatory dysregulation and underlying chronic infection.
• VIP + LL-37: occasional combination for chronic inflammatory states with potential biofilm component (LL-37 has antimicrobial activity).
• VIP + BPC-157: rationale of combining VIP's anti-inflammatory effects with BPC-157's tissue-repair effects. Sometimes used for gut-brain axis dysregulation.
• VIP + KPV: less common, both anti-inflammatory peptides with different mechanisms.
• VIP + standard Shoemaker prerequisites (cholestyramine binder, nasal antifungals for MARCoNS, hormone correction): the formal protocol structure where VIP is the final step.

Combinations to avoid or use with caution:

• Active uncontrolled biotoxin exposure: VIP is generally considered ineffective or counterproductive while biotoxin exposure continues
• Active untreated MARCoNS: prerequisite for VIP in Shoemaker framework
• Active malignancy: theoretical caution due to mild angiogenic effects
• Pregnancy and breastfeeding: avoid
• Severe hypotension or significant cardiovascular disease: caution due to vasodilatory effects
• Active asthma exacerbation: paradoxical bronchospasm risk with intranasal route in some patients

The most actionable framing of VIP in 2026: this is a well-characterized endogenous neuropeptide with substantial basic science evidence for anti-inflammatory and immunoregulatory effects. Clinical trial validation is limited but includes a meaningful Phase 2 study in sarcoidosis (Prasse 2010). The dominant contemporary off-label use is in chronic inflammatory response syndrome (CIRS) under the Shoemaker protocol, particularly for mold-illness and post-Lyme inflammatory states. The CIRS evidence base is primarily uncontrolled clinical observation from one principal research group, in a diagnostic framework not universally recognized. Patients considering VIP for CIRS should work with a CIRS-trained physician familiar with the full protocol structure, understand that VIP is the final step (not a first-line intervention), and recognize the evidence quality limitations. For non-CIRS uses (sarcoidosis, asthma, autoimmune conditions), VIP remains investigational with much weaker evidence than mainstream alternatives. The 503A compounding regulatory status could change with FDA enforcement actions.

For informational and educational purposes only. Not medical advice. Not for human consumption unless prescribed by a licensed physician for an FDA-approved indication. Consult a qualified healthcare provider before using any peptide or pharmaceutical product.