Vasoactive Intestinal Peptide

VIP belongs to the small set of endogenous immunomodulators in this corpus where the mechanism is unambiguous and the clinical-translation evidence is uneven — a structural parallel to Thymosin α-1, where a characterised regulatory peptide with plausible relevance to many chronic inflammatory contexts has produced trial evidence in some indications and very little in others. The two largest investigational programmes are pulmonary hypertension and COVID-19 acute respiratory distress; the practitioner conversation that surrounds the molecule in 2026 sits almost entirely outside both.

The pulmonary-hypertension program is the older clinical bet. Petkov et al., J Clin Invest 2003, 111(9):1339–1346 reported reduced VIP serum concentrations and upregulated pulmonary VIP receptor expression in patients with primary pulmonary hypertension, and tested 200 μg/day inhaled VIP in an eight-patient open-label trial. Reductions in mean pulmonary artery pressure, increases in cardiac output, improved oxygen saturation, and significant six-minute-walk gains at 12 and 24 weeks established inhaled VIP as a mechanistically rational pulmonary-vasodilator candidate. The signal did not survive into a Phase III program, and the pulmonary-hypertension landscape has been built around endothelin antagonists, phosphodiesterase-5 inhibitors, and prostacyclin analogues. The 2003 result is mechanism-confirmatory at small scale rather than therapeutically established.

The COVID-19 acute respiratory distress program — under the synthetic-VIP brand aviptadil (ZYESAMI / RLF-100), developed by NeuroRx and Relief Therapeutics — is the most rigorous clinical trial body any peptide on this list has assembled inside a single indication, and the headline result is negative. Youssef et al., Crit Care Med 2022, 50(11):1545–1554 randomised 196 patients with critical COVID-19 respiratory failure 2:1 to three days of intravenous aviptadil or placebo; the primary endpoint — alive and free from respiratory failure at day 60 — did not reach statistical significance (odds ratio 1.6, 95% CI 0.86–3.11). Statistically significant secondary signals emerged on 60-day survival (OR 2.0, p=0.035), respiratory distress ratio, day-3 IL-6 reduction, and a tenfold survival improvement in the mechanically ventilated subgroup, with no drug-related serious adverse events. The larger NIH-coordinated TESICO trial — Lancet Respir Med 2023, 11(9):791–803, 461 modified-intention-to-treat participants — was stopped on May 25, 2022 for futility, and concluded aviptadil did not significantly improve clinical outcomes up to day 90 versus placebo. The FDA declined Emergency Use Authorization on November 4, 2021, citing insufficient evidence. The honest framing: more rigorous COVID-19 trial scrutiny than any other peptide-class molecule received in that era, mixed-to-negative primary endpoints, suggestive subgroup signals, no regulatory approval. The broader pattern parallels other entries in the failed peptide trials archive.

The off-label biohacker use case operates downstream of the Shoemaker chronic inflammatory response syndrome (CIRS) framework. CIRS — as articulated by Ritchie Shoemaker and the surviving-mold community — postulates a genetically susceptible subpopulation in whom biotoxin exposure (water-damaged-building mycotoxins, cyanobacterial toxins, post-Lyme inflammation, dinoflagellates) drives a persistent innate-immune dysregulation phenotype with characteristic biomarker patterns: low MSH, low VIP, elevated C4a, TGF-β1, and MMP-9, dysregulated VEGF. Intranasal VIP sits at step 12 of the published Shoemaker protocol, deployed only after biotoxin exposure has been removed and earlier steps completed. The cornerstone observational report is the open-label series in Shoemaker, House and Ryan, Health 2013, 5(3):396–401 — 20 CIRS patients refractory to prior protocol steps, treated with replacement intranasal VIP for at least 18 months, reporting symptom reduction toward control levels, normalised inflammatory markers, raised circulating VIP and MSH, normalised exercise pulmonary artery systolic pressure, and improved quality of life. A subsequent open-label MRI volumetric study from the same group reported grey-matter nuclear-volume restoration on intranasal VIP. Both reports are observational, open-label, and single-investigator-group; there are no published randomised trials of intranasal VIP for CIRS, mold-related illness, post-Lyme syndrome, or post-COVID fatigue. The mechanism — anti-inflammatory cytokine shift, regulatory-T-cell induction, mast-cell modulation, NF-κB suppression — is biologically plausible against the phenotype the framework names. The evidence testing whether exogenous intranasal VIP drives that effect in patients is observational within a niche practitioner community.

The long-COVID extension of the CIRS framework is the natural mechanistic bridge but lacks dedicated trial support. The long COVID and peptides dossier walks the broader landscape; VIP enters the conversation on three lines — the mast-cell-activation overlap documented in long COVID and discussed alongside KPV in that dossier, the surfactant and pulmonary endothelial reading of post-acute COVID respiratory phenotypes, and the structural similarity of the CIRS biomarker pattern to subsets of long-COVID inflammatory profiles. None of those mappings have been clinically tested with VIP in long COVID patients, and the inference that an agent failing acute-ARDS primary endpoints generalises to chronic post-viral phenotypes is one no published trial supports.

The honest framing rests on three points. The endogenous biology is unambiguous — the Said and Mutt 1970 and Delgado, Pozo and Ganea 2004 reference base is one of the more mature endogenous-immunomodulator literatures in this corpus, and VPAC1/VPAC2 pharmacology is settled. The most rigorous controlled-trial body — the ZYESAMI COVID ARDS program — produced a primary-endpoint miss, a futility-stopped Phase III, and an FDA EUA rejection. The off-label CIRS and long-COVID use case rests on mechanism extrapolation plus practitioner observation; the controlled-trial evidence for that use case is absent. The /critic/no-human-rcts framing applies. Cross-class peers in this corpus include Thymosin α-1 on broader immunomodulation, KPV on the NF-κB and mast-cell-stabilising line, and BPC-157 on inflammation-context vascular and gut-barrier overlap.