VIP

Origin and Structure

Vasoactive intestinal peptide (VIP) is a 28-amino-acid endogenous peptide originally isolated from porcine duodenum in 1970 by Sami Said and Viktor Mutt. Despite its name — which reflects the first observed activity (relaxation of intestinal smooth muscle) — VIP is expressed throughout the central and peripheral nervous systems, the cardiovascular and pulmonary systems, and the immune system. It is a member of the secretin/glucagon peptide superfamily and shares substantial sequence homology with PACAP (pituitary adenylate cyclase-activating peptide).

Synthetic VIP is marketed as Aviptadil and has received FDA Breakthrough Therapy designation for respiratory failure associated with critical COVID-19 and for pulmonary arterial hypertension, though as of 2026 it has not received full marketing approval in the United States.

Mechanism of Action

VIP signals through two G-protein-coupled receptors, VPAC1 and VPAC2, which activate adenylate cyclase and raise intracellular cAMP. The downstream effects are broad and tissue-specific:

• Vasodilation and bronchodilation via smooth-muscle cAMP elevation — the basis for the pulmonary-hypertension and ARDS programs.
• Anti-inflammatory immune modulation, including Treg expansion, suppression of Th17 differentiation, and downregulation of TNF-α, IL-6, and IL-12 production by macrophages and dendritic cells.
• Type II pneumocyte support — VPAC1 is highly expressed on alveolar type II cells, where VIP promotes surfactant production and inhibits apoptosis.
• Circadian and neuroendocrine signaling, particularly in the suprachiasmatic nucleus, where VIP is a core synchronizing signal.

Clinical Evidence

VIP's clinical data is genuinely split between two worlds. On the mainstream drug-development side:

• A 28-day open-label study of inhaled VIP in pulmonary sarcoidosis (Prasse et al.) reported reduced TNF-α in bronchoalveolar lavage and increased regulatory T cells — the best-controlled mechanistic evidence for VIP's immunomodulatory effect in humans.
• Phase 2 and Phase 3 trials of intravenous Aviptadil in critical COVID-19 respiratory failure produced mixed results, with some observational signals of mortality benefit but failure of the pivotal randomized trials to meet their primary endpoints.
• Ongoing work in pulmonary arterial hypertension has used inhaled formulations with modest hemodynamic effects.

On the alternative-medicine side, VIP is the final step of the Shoemaker protocol for Chronic Inflammatory Response Syndrome (CIRS) — a controversial diagnostic framework associated with mold/biotoxin illness. Published evidence for the CIRS framework itself is limited and contested, and VIP use in that context is guided by practitioner-reported observational data rather than randomized trials. This is a real gap, and anyone evaluating intranasal VIP in the mold-illness context should understand that they are operating in a clinical space the mainstream pulmonology and infectious-disease communities do not recognize.

Practical Considerations

Clinical-trial dosing varies dramatically by indication and route — inhaled for sarcoidosis, intravenous for severe COVID-19, intranasal for the Shoemaker CIRS protocol (typically 50 mcg twice daily). VIP is rapidly degraded in plasma (half-life ~2 minutes for the native peptide), which is why clinical programs have converged on local delivery (inhaled, intranasal) or sustained-release formulations. Subcutaneous dosing of native VIP is pharmacokinetically inefficient and is not the route used in any approved or advanced-trial program.

For readers interested in related endogenous neuropeptides, Cerebrolysin operates in a nearby neurotrophic space, though with a very different mechanism.

Safety Considerations

VIP's most predictable adverse effects follow directly from its vasodilatory activity: flushing, hypotension, tachycardia, and headache, particularly with parenteral dosing. Diarrhea and mild GI disturbance are also common. More serious concerns in the critically ill include arrhythmia during IV infusion, which is why hospital-based programs use close cardiovascular monitoring.

A separate and underappreciated concern is that VIP is mitogenic for several tumor types, including small-cell lung cancer and some neuroendocrine tumors, via VPAC1 signaling. Long-term exogenous VIP use has not been characterized for oncologic risk, and caution is warranted in patients with a history of VIP-receptor-expressing malignancy.

Regulatory Status

VIP/Aviptadil is not fully FDA-approved but holds Breakthrough Therapy designation for specific respiratory indications. It is not on the WADA prohibited list. In the United States, non-hospital use is primarily through compounding pharmacies, which has tightened substantially under recent FDA peptide-compounding enforcement.

The Bottom Line

VIP is a mechanistically serious endogenous peptide with a split identity: a legitimate drug-development program in pulmonary and inflammatory medicine, and a parallel alternative-medicine protocol in the CIRS/mold-illness community that lacks equivalent randomized-trial support. Both audiences cite the same molecule, but the evidence standards on each side are not comparable. Readers should treat them as distinct conversations.