What it is: A 28-amino-acid neuropeptide naturally produced in the gut, lungs, brain, and immune system with a broad role spanning immune regulation, gut motility, and circadian rhythms.
Research suggests: Human clinical trials have studied inhaled VIP (Aviptadil) for pulmonary arterial hypertension, Crohn's disease, and COVID-19 respiratory complications, with mixed results.
Best for: Immune, gut, and pulmonary researchers
Key thing to know: One of the most pleiotropic peptides studied - its effects are highly tissue-specific, so research findings from one organ system do not necessarily predict effects in another.
What is VIP?
VIP (Vasoactive Intestinal Peptide) is a 28-amino-acid neuropeptide produced throughout the body — gut, lungs, brain, and immune system. First identified for its vasodilatory effects on blood vessels, it was later found to have a far broader role. VIP is now among the more thoroughly studied endogenous neuropeptides, with functions spanning immune regulation, gut motility, neuroprotection, circadian synchronization, and pulmonary function.
VIP acts on two main receptor types, VPAC1 and VPAC2, which are distributed throughout the body in different proportions by tissue type. VPAC1 is more highly expressed in the immune system and gut. VPAC2 is more expressed in the brain and smooth muscle.
This differential distribution gives VIP tissue-specific effects that depend on which receptor is predominant in a given organ, which also means that its research profile is genuinely complex and cannot be reduced to a single primary effect.
Research interest spans inflammatory conditions including inflammatory bowel disease and rheumatoid arthritis, pulmonary arterial hypertension, neuroprotection in neurological conditions, circadian rhythm disorders, and general immune support. An inhaled pharmaceutical form of VIP was studied in clinical trials for pulmonary arterial hypertension, giving it a more developed human pharmacology profile than many neuropeptides in this library.
How it works.
In research, the proposed mechanism has several parts.
Anti-inflammatory action: VIP is a broad anti-inflammatory and immunomodulatory signal throughout the body. It shifts pro-inflammatory T helper 1 (Th1) responses toward regulatory T helper 2 (Th2) responses — lowering cytokines such as TNF-alpha, IL-6, and IL-12 while raising anti-inflammatory mediators like IL-10. This matters for autoimmune and chronic inflammatory conditions where Th1 dominance is central.
In the gut: In the gut, VIP regulates intestinal motility by relaxing smooth muscle and has protective effects on intestinal epithelial cells, supporting the integrity of the gut barrier. It also influences mucosal immune function in the gut-associated lymphoid tissue, connecting its systemic immunomodulatory role to gut health specifically.
In the nervous system: In the nervous system, VIP acts as both a neuroprotective factor and a neurotransmitter. It promotes neuronal survival under conditions of oxidative stress and excitotoxicity. In the lungs, it is a potent vasodilator and bronchodilator, explaining its clinical trial history in pulmonary arterial hypertension.
Circadian role: Its circadian role is particularly notable. VIP is produced by neurons in the suprachiasmatic nucleus, the brain's master circadian clock. It helps synchronize peripheral clocks throughout the body by transmitting timing signals from the central clock to other tissues.
A systemic signal: Research suggests that VIP signaling is essential for maintaining the coherence of the body's distributed circadian system, with implications for sleep quality, metabolic timing, and immune function rhythms.
What the research shows.
The research evidence breaks down as follows.
Research base: VIP has a substantial basic science and clinical research base. Human studies exist across multiple conditions. In pulmonary arterial hypertension, an inhaled form of VIP (Aviptadil) progressed to Phase 2 clinical trials, providing direct human pharmacokinetic and safety data.
Pulmonary studies: Results showed reductions in pulmonary vascular resistance and improvements in exercise capacity in some patients, establishing that VIP can produce measurable clinical effects in humans.
Inflammatory conditions: In inflammatory bowel disease and rheumatoid arthritis, studies have shown anti-inflammatory effects consistent with known VPAC receptor pharmacology. The immunomodulatory mechanism is well-characterized from in vitro and preclinical work, with supportive human data from observational and small interventional studies. Neuroprotection research shows consistent preclinical results, with more limited but suggestive human evidence from relevant neurological populations.
The limitations: The limitations reflect the breadth of VIP research rather than a narrow evidence gap. Because VIP has such diverse effects across organ systems, individual trials tend to focus on one application, and generalizing to other uses requires mechanistic reasoning rather than direct evidence. Large-scale RCTs for general immunomodulatory or wellness applications are absent.
Evidence level: The evidence is meaningful but condition-specific.
Biomarkers to review first.
Research protocols for VIP typically reference the following biomarkers as important baseline context. Given its broad immune and inflammatory effects, understanding your baseline inflammatory and hormonal status is especially relevant before any protocol consideration.
What it's commonly researched with.
In research literature, VIP is frequently discussed alongside other immunomodulatory and gut-supporting peptides. The combinations below reflect what researchers have studied, not recommendations for use.