Question 1

What does VIP do to the body, system by system?

Accepted Answer

It relaxes smooth muscle almost everywhere it is found, and the strength of the evidence changes from one system to the next. A 2001 review places VIP in the gut, heart, lungs, thyroid, kidney, urinary bladder, genital organs and the brain, and its common action in vessels is that VIP is 50-100 times more potent than acetylcholine as a vasodilator. A vasodilator widens blood vessels. Here is how the measured effects line up. Vessels and the heart have animal data and human procedure data. The lungs have human tissue strips and, through aviptadil, trials in patients with lung failure and high lung pressure. Brain cells have one study in a dish. Skin, wound healing, bone and erection have reviews describing the body's own VIP. The gut has studies that measure VIP levels rather than give it. So the honest map has two well-lit regions, the circulation and the failing lung, and a lot of territory where the evidence is about what the body's own VIP does rather than what a dose of it would do. The sections below take each system in turn.

Question 2

How quickly do VIP's effects start, and how long do they last?

Accepted Answer

Fast in every setting where it has been timed, and short in the one setting where people were watched. In forearm skin, the 2010 volunteer study measured blood flow by laser Doppler flowmetry, visual flare and wheal, and found pain lasting about 100 s after injection. Laser Doppler flowmetry reads blood flow through the skin with a beam of light. In lung tissue, by contrast, the VIP-induced relaxation, especially of pulmonary artery, has a long duration. When labelled VIP was injected into a vein, the lung was the primary site of uptake, with peak lung activity at 0.7 hr. So the lungs take up VIP within the hour, and lung tissue holds the relaxation longer than skin holds its flush. A long effect in a strip of tissue in a bath is not the same as a long effect in a breathing person, and that second figure is not reported among the research behind this page.

Question 3

Did intravenous aviptadil help COVID-19 respiratory failure?

Accepted Answer

Not in the largest trial, and that is the result to start from. TESICO randomised adults with COVID-19 respiratory failure at 28 US sites to aviptadil infusions or matched saline, and 94% of those treated were in intensive care. Its main measure sorted people at day 90 into six categories, running from at home and off oxygen down to dead. The odds of being in a better category with aviptadil rather than placebo were 1·11, with a 95% confidence interval of 0·80 to 1·55, a range that straddles no effect. Its authors concluded that aviptadil did not significantly improve clinical outcomes up to day 90 when compared with placebo. An earlier trial of 196 patients reads differently on the surface. Its primary end point, patients being alive and free from respiratory failure at day 60, did not reach statistical significance, while a further analysis found a statistically significant two-fold odds of improved survival. A primary result that misses beside a secondary one that hits is a signal to test again, and the larger, later TESICO trial did not confirm it.

Question 4

Did the inhaled form or the smaller studies do better?

Accepted Answer

They report more, on weaker designs. In a double-blind trial of 80 hospitalised COVID-19 patients from 9 centres, the average time to discharge was 7.8 ± 4.0 days in aviptadil group and 10 ± 5.0 days in placebo, a gap that only just reached statistical significance at p = 0.049. In those patients, breathlessness scores were not statistically different on day 3 and were lower on day 7, and lung damage on CT scans had improved more by day 28. The death rate was 5.1% on aviptadil against 12.2% on placebo, which in a trial of this size amounts to a handful of patients. A published letter raised methodological considerations about the trial, and the authors replied. Across lung failure more widely, a 2025 meta-analysis pooled nine studies with 665 patients and found a survival odds ratio of 1.01 for aviptadil against placebo in the two randomised trials. Its seven case series showed better oxygen levels, and its authors concluded that current evidence does not indicate a significant survival benefit.

Question 5

Could VIP help high blood pressure in the lungs?

Accepted Answer

This is the benefit closest to a clinic, and it is still in development. In the 1984 strip study, VIP was approximately 200 times as potent as prostacyclin, on a molar basis, as a relaxant of human pulmonary arterial strip. On a molar basis means molecule for molecule. A 2013 review explains the logic: pressure in the lungs depends on a balance between signals that widen vessels, VIP among them, and signals such as endothelin-1 that narrow them and make their walls grow. The idea is that adding VIP tips that balance back toward wider, calmer vessels. A 2020 review lists synthetically produced vasoactive intestinal peptide among the newer agents under clinical development for pulmonary arterial hypertension. Under development is not the same as shown to work, and the one patient study shows the gap. In 2008, 20 patients with pulmonary hypertension inhaled aviptadil once during right-heart catheterisation, and it caused a small and temporary but significant selective pulmonary vasodilation, with six patients seeing lung vessel resistance fall by more than a fifth. The authors called the effect modest and short-lived, and said higher doses and chronic treatment still needed to be tested.

Question 6

Does VIP open the airways?

Accepted Answer

In tissue, yes. In a living animal with allergies, the picture flips. A 2013 review of lung nerves places vasoactive intestinal peptide (VIP) on cholinergic nerves, part of a third nerve system in the airways that is able to produce both effects, tightening and relaxing. Cholinergic nerves are the ones that use acetylcholine, the main signal to airway muscle. In the 1984 study, VIP relaxed strips of human bronchus kept alive in a lab bath. That observation is the basis for calling VIP a possible bronchodilator, meaning something that widens the airways, and it stayed an observation on tissue rather than a test in a person. The counterweight, a mouse study in which the animals' own VIP fed allergic airway inflammation, is set out on the VIP safety page. A strip that relaxes and an allergic airway that inflames are different questions, and only the first one looks like a benefit.

Question 7

Does VIP improve blood flow to the heart?

Accepted Answer

In procedures in animals and people, it raised coronary blood flow. The more interesting finding is about what the heart does with its own VIP under stress. The 2001 review reports that in research animals and in humans, VIP, administered into the coronary artery or intravenously, significantly increases coronary artery blood flow. It adds that the heart releases more of its own VIP while a coronary artery is blocked and again when blood flow returns, where VIP may promote local blood flow and may have a free-radical scavenging effect. Occlusion is a blocked artery, reperfusion is blood rushing back when it reopens, and free radicals are reactive molecules that damage tissue at that moment. Note the word may, twice. The heart appears to release more VIP when it is starved of blood, which hints at a protective role. None of the studies covered here gave VIP during a heart attack to see whether it helps, and that is the study that would turn a hint into a finding.

Question 8

Is VIP being developed for high blood pressure?

Accepted Answer

As a target, yes, at an early stage. A 2018 review of future blood pressure medicines names vasoactive intestinal peptide agonists among unique systems in development never before used in HTN. HTN is high blood pressure, and an agonist is a molecule that switches on the same receptor as VIP, often built to last longer. The reason is plain in the 2001 review, which reports VIP reducing mean arterial pressure by 10-15% while strengthening the heartbeat. That the development work is on agonists rather than on VIP itself is worth noticing, since the natural peptide acts strongly but, in skin at least, for minutes. Whether the pressure drop is a benefit or a hazard depends entirely on whose pressure it is, which is why the same figure also appears on the VIP safety page.

Question 9

Does VIP protect brain cells?

Accepted Answer

In one dish, against one poison. A 2016 study exposed NE-4C neural stem cells to manganese and found that VIP treatment at 1 μM was sufficient to yield maximum protection. Neural stem cells are the cells that can become new nerve cells, and manganese in excess damages them. In those cells, a protein that drives cell death and reactive oxygen production significantly decreased in cells after incubation with VIP in the presence of Mn. A 2012 review is more ambitious, saying studies render it as an attractive candidate to be considered in several neurological disorders linked to neuroinflammation or abnormal neural development. Attractive candidate is the language of a research proposal. A mouse cell line protected from one metal is a long way from a human brain, and the gap between the two is the finding.

Question 10

Does VIP help skin and wound healing?

Accepted Answer

Reviews describe a role for the body's own VIP. No dose of it was given for healing in the research behind this page. A 2025 review explains that neurons release neuropeptides like substance P (SP), calcitonin gene-related peptide (CGRP), and vasoactive intestinal peptide (VIP) along with neurotrophic factors during wound repair. Early in healing, the review says these signals initiate vasodilation and promote platelet aggregation during the hemostasis phase, the stage when bleeding stops. Platelet aggregation is platelets clumping to form a clot. The same review looks ahead to approaches such as neuropeptide delivery, which is a proposal for future work rather than a tested method. An older review of skin immunity discusses the putative inflammatory and immunologic roles of vasoactive intestinal peptide in the skin. Putative means supposed. Two reviews describing a natural role is a reason to study VIP in wounds, and it does not tell you that adding VIP speeds healing.

Question 11

What are the benefits of VIP for men?

Accepted Answer

Erection is the one men's health use with patient data, and the version tested is a combination rather than VIP alone. A 2002 review of the penile arteries states that acetylcholine, vasoactive intestinal peptide as well as peptides in sensory nerves probably also play a role in penile vasodilation, with nitric oxide as the main signal. The injection built on that role pairs VIP with phentolamine, a second vessel-widening agent, and is injected into the penis. A 2025 retrospective series followed 308 men who had all tried the standard injection, alprostadil, and 96% had already failed tablets of the sildenafil type. Overall, 182 men (59%) found the combined injection effective, judged by being able to resume penetrative sex at three months. It worked in 76% of men who had stopped alprostadil because of pain, and in 36% of those for whom it had failed at its top dose. The authors list the limits themselves: a retrospective design and lack of validated instruments to objectively assess erectile function. That is a useful clinic record, and it is not a randomised comparison with placebo.

Question 12

What are the benefits of VIP for women?

Accepted Answer

None has been measured in the research behind this page, and the one women's health study shows why the question is hard to ask. A 2023 study of endometriosis stained pelvic tissue from 94 symptomatic women and found nerve fibres that often colocalized with SP-, CGRP-, TH-, and VIP-positive nerve fibers. Endometriosis is tissue like the womb lining growing outside the womb, and colocalized means found in the same place. The study was about a different receptor, and VIP was one of several markers used to label the nerves. That makes VIP part of the map of pain nerves in endometriosis, not a candidate remedy for it. Nothing in that work, or anywhere else among these sources, gave VIP to women or measured a result in them, which is a gap rather than a negative finding.

Question 13

What does VIP do for digestion?

Accepted Answer

In dogs, it drives fluid from the pancreas. In the gut studies people usually point to, it is the thing being measured. A 1993 dog study found that VIP (1-100 nmol/kg) caused dose-dependent increases in the secretion of pancreatic juice and bicarbonate outputs, but had little effect on the protein outputs. Bicarbonate neutralises stomach acid, and the protein outputs are the digestive enzymes, so VIP moved the water and not the enzymes. The gut-motility studies point the other way. In an animal study of broiler chickens fed hesperidin, gut emptying got better in every treated group while the feed was lowering VIP levels. So in that animal work, better gut movement went with less VIP, not more. Those studies measure VIP as a marker, and they cannot be read as evidence that taking VIP helps constipation or a slow stomach.

Question 14

Does VIP affect sleep or the body clock?

Accepted Answer

The body clock work is real and detailed, and none of it gave VIP to an animal or a person to change their sleep. A 2023 lab study showed that VIP-induced coupling in clock mutant mouse cells engineered to express the VIP receptor is sufficient to synchronize, and maintain, robust circadian oscillations. Circadian oscillations are the roughly 24-hour cycles each cell keeps. In plain terms, VIP kept a dish of cells ticking together. A 2020 review names arginine vasopressin (AVP) and vasoactive intestinal peptide (VIP) as the neuromodulators whose study changed the picture of the brain's master clock. In mice, a 2022 study tied REM sleep to vasoactive intestinal peptide-mediated dendritic disinhibition in the prefrontal cortex. That last finding concerns VIP-carrying brain cells, not the peptide as a dose. Clock cells in a dish and a person's sleep are different things.

VIP: what the research measured