Question 1

What is VIP, and what does it do?

Accepted Answer

VIP is vasoactive intestinal peptide, a hormone the body makes inside its own nerves. A 2001 review in Cardiovascular Research describes where it sits. Significant concentrations of VIP are present in the gastrointestinal tract, heart, lungs, thyroid, kidney, urinary bladder, genital organs and the brain. That spread is the first thing to understand, because it means VIP is not an organ-specific signal. Its main job is relaxing things. On a molar basis, VIP is 50-100 times more potent than acetylcholine as a vasodilator, the same review reports. A vasodilator widens blood vessels, and acetylcholine is the nerve signal that normally does that job. VIP functions as a nonadrenergic, noncholinergic neurotransmitter or neuromodulator, which is the formal name for a nerve signal outside the two best-known systems.

Question 2

Why does VIP mean two different things in the research?

Accepted Answer

This trips up anyone reading the literature for the first time. In neuroscience, VIP usually names a type of brain cell rather than something given to anybody. A 2019 review describes vasoactive intestinal peptide-positive (VIP) GABAergic interneurons as tightly linked with the cholinergic system. They are called VIP cells because they carry the peptide, not because anyone injected it. The two bodies of work share three letters and little else. A 2017 mouse experiment is typical. Activating vasoactive intestinal peptide (VIP)-positive interneurons enhanced behavioral performance and neuronal action plan representation in those mice. A light switch aimed at a mouse's own cells is a different experiment from giving a person the peptide. Counting that work as evidence about VIP as a compound would inflate the record badly.

Question 3

Has VIP been given to people?

Accepted Answer

Yes, in two quite different kinds of study, and they are worth keeping apart. The first kind is the research probe. A 2010 study explored pain perception and vasomotor responses in 16 healthy volunteers in a double-blind, placebo-controlled, crossover study, with each injection going into the forearm skin. A 1995 imaging study presents the biodistribution, safety and absorbed dose of 123I-VIP administered to 18 patients with intestinal adenocarcinomas or endocrine tumors, with the peptide carrying a radioactive label so it could be followed on a scan. Probes like these are built to provoke a response and measure it, rather than to make anybody better. The second kind is aviptadil, the synthetic form, given to sick patients over several days with recovery as the goal. One trial run across ten US hospitals randomised 196 patients with COVID-19 respiratory failure to receive 3 days of IV Aviptadil or placebo. That second record is larger and newer, and aviptadil itself is described in the next section.

Question 4

What is aviptadil?

Accepted Answer

Aviptadil is the name given to VIP made in a laboratory, and over the years the name has covered two different things. A 2023 chemistry paper describes aviptadil as a 28-mer therapeutic peptide, a chain of 28 amino acids, with potential therapeutic effects especially in acute respiratory distress syndrome (ARDS). ARDS is a form of lung failure in which fluid floods the air sacs. The older version was a mix of two agents. A 2001 review defines aviptadil as an injectable formulation of vasoactive intestinal polypeptide (VIP) in combination with the adrenergic drug phentolamine, made for erectile dysfunction. Phentolamine also widens blood vessels, so a result for that injection does not tell you what VIP does alone. The lung form has been given into a vein as a slow drip and breathed in as a mist. A 2008 review listed aviptadil (an inhalable vasoactive intestinal peptide) among candidates in late-stage trials for high blood pressure in the lungs. What its trials found is set out on the VIP benefits page, and what they logged as harm on the VIP safety page.

Question 5

What did the injection studies measure?

Accepted Answer

Three things were measured: pain, skin blood flow and the mark an injection leaves. Pain intensities after PACAP38 and VIP were mild and limited to a short time of about 100 seconds after injection, the 2010 study reports. PACAP38 is pituitary adenylate cyclase-activating peptide-38, a close chemical relative used there as the comparison injection. The vascular response was larger and more informative than the pain measurement. Skin blood flow increase, flare and wheal were larger after both PACAP38 and VIP compared to placebo. A flare is the reddened spread surrounding an injection, and a wheal is the raised swelling at its centre. VIP induced a considerably larger increase in skin blood flow, flare and wheal than PACAP38 did. Read it for what it is: a localised vascular reaction in the forearm skin of healthy volunteers, lasting minutes, rather than an outcome anybody would notice in ordinary life.

Question 6

What do the headache trials show?

Accepted Answer

Two registered trials set out to provoke headache with VIP, and a published trial has since tested migraine directly. One registry entry is listed as Experimental Headache Induced by Vasoactive Intestinal Polypeptide, and it is marked COMPLETED. The other ran as The Effects of a Long-lasting Infusion of Vasoactive Intestinal Peptide (VIP) on Headache, Cranial Hemodynamic and Autonomic Symptoms in Healthy Volunteers. Cranial hemodynamic means blood flow in the head, and that entry is also marked COMPLETED, with neither showing a published report among the sources cited on this page. The published one, from 2008, gave twelve patients with migraine without aura an infusion of VIP and, on a separate day, placebo. Its authors had expected VIP might induce migraine attacks in migraineurs. Instead they concluded that VIP mediates a marked dilation of cranial arteries, but does not trigger migraine attacks in migraineurs. Widening the arteries of the head was not enough, on its own, to start a migraine in that small group, and the headache detail is weighed on the VIP safety page.

Question 7

What does a VIP blood level mean?

Accepted Answer

Most human VIP numbers in the literature are readings rather than doses. A 2008 dialysis study measured plasma concentrations of intact parathyroid hormone (PTH), vasoactive intestinal peptide (VIP), ghrelin, substance P, serotonin, cholecystokinin (CCK) and gastrin. VIP was one gut hormone among seven there, tracked across a test meal. The level moved, and the authors report a significant decrease in VIP concentration at 4 h. Gut studies use the same approach. A 2022 observational study of 70 children with constipation compared plasma VIP levels before and after treatment between the 2 groups. In all of these, VIP is the thing being watched rather than the thing being given. A reading tells you where somebody sits on a given day, and nothing more than that.

Question 8

What are the symptoms of high VIP levels?

Accepted Answer

This question joins two different things, and they are worth pulling apart. A high reading is a laboratory number from a blood sample, usually taken while somebody already carries a diagnosis. No study among the research behind this page follows people with a high reading to see what they go on to develop. What is documented is the opposite half of the question, which is what happens in the minutes after VIP is infused. That picture is consistent across the human work, and it is vascular. Skin blood flow increase, flare and wheal were larger after VIP than after placebo, and two registered trials were constructed around headache. A 2001 review adds the cardiac side, reporting that endogenously released or exogenous VIP can significantly increase the heart rate. So a raised level and a raised reading are different questions, and only the first has ever been produced deliberately.

Question 9

What does VIP do in the lungs?

Accepted Answer

The lung work is old, specific and mostly done outside a body. In a 1984 study VIP relaxed isolated strips of human bronchus, pulmonary artery, and lung parenchyma in vitro. Those were tissue strips in a bath, taken from people, which is as close to a lung as a dish gets. The potency was striking. Against that arterial strip, VIP is approximately 200 times as potent as prostacyclin, on a molar basis. A 2020 review lists prostanoids among the disease specific treatment developed for pulmonary arterial hypertension, and prostacyclin belongs to that class. The same review still lists synthetically produced vasoactive intestinal peptide among agents under clinical development. Patients have since breathed it in: in a 2008 study, 20 patients with pulmonary hypertension inhaled a single dose of aviptadil during a heart catheter procedure, and the vessel-widening it produced in their lungs was modest and short-lived. The potency measured in a bath did not translate into a large effect in a living lung.

Question 10

What does VIP do to the heart and circulation?

Accepted Answer

This is the setting where VIP has actually been put into people and measured. A 2001 review reports what happens in research animals and in humans when VIP goes into a coronary artery or into a vein. Blood flow through the coronary arteries rises, and the resistance those vessels offer falls. The epicardial coronary arteries are the vessels running across the surface of the heart. Heart rate moves as well. The same review reports that VIP can significantly increase the heart rate, with a more potent effect than norepinephrine has. Norepinephrine is the body's own fight-or-flight signal, so that is a strong comparison. These are acute measurements, taken during a procedure. They describe what the circulation does in the moment, rather than what happens to anybody over a month.

Question 11

How long does VIP take to work?

Accepted Answer

Quickly, and not for long, which is the practical shape of this molecule. In the human skin study, pain was mild and limited to a short time of about 100 seconds after injection. The imaging work provides the clearest pharmacological number. The mean effective half-life of the labelled peptide was 2.2 hours in the lungs and 6 hours in the urinary bladder, that 1995 study reports. Half-life is the time taken for half of what went in to disappear. Clearance was rapid on the other measure as well. Radioactivity was excreted into the urine and amounted to 37% of the injected dose within four hours. Chemists have tried to stretch that interval. A 2017 review points to PEGylation and glycosylation as the modifications applied to VIP analogues, which attach extra molecules to slow breakdown. Nothing in these sources reports how long a response persists after an injection outside a laboratory.

Question 12

What makes the body release VIP?

Accepted Answer

The 2001 review gives a direct list. VIP release in the body is stimulated by high frequency (10-20 Hz) nerve stimulation and by cholinergic agonists, serotonin, dopaminergic agonists, prostaglandins (PGE, PGD), and nerve growth factor. Cholinergic agonists are drugs that mimic acetylcholine, the main nerve signal to the gut and the airways. Nerve traffic is the headline in that list. A 2018 review adds that the vagus nerve releases other neurotransmitters such as vasoactive intestinal peptide (VIP), which also modulates liver injury responses and hemodynamics. The immune system can trigger it too. A 2015 study found that IL-5, a cytokine produced by activated immune cells, acts directly on nociceptors to induce the release of vasoactive intestinal peptide (VIP). Nociceptors are the nerve endings that register damage. So a person's own VIP rises in answer to nerve and immune signals, rather than on any schedule.

Question 13

What is documented about side effects?

Accepted Answer

The documented effects depend on how VIP was given, and the hub only sketches them. In single research injections they were brief and local: pain intensities after PACAP38 and VIP were mild and limited to a short time of about 100 s after injection. A 2001 review adds that VIP has a more potent effect on heart rate than does norepinephrine. The aviptadil trials give a firmer count. In TESICO, a composite of death, serious adverse events, organ failure, serious infection or severe adverse events in the first five days struck 63% of patients on aviptadil and 56% of those on placebo, a gap the trial did not find statistically significant. Those were critically ill patients, which is why the comparison with placebo matters more than either raw percentage. The trial exclusions, the regulatory holds and the migraine result are taken apart on the VIP safety page.

Question 14

Is VIP approved for anything?

Accepted Answer

One VIP product was, in a few countries, and the approval does not stretch beyond it. A 2001 review traces the erectile dysfunction injection that paired VIP with phentolamine. By April 2000, it had been approved in New Zealand, and in October 2000, marketing approval in the UK was granted by the MCA, the British medicines regulator of that time. A 2019 systematic review of penile injections describes aviptadil/phentolamine combination therapy as a recent addition to approved agents in a select few geographical regions. That approval covers that combined injection, for that use. It does not cover VIP on its own, an inhaled or intravenous form, or a vial sold for research. The lung-failure form sits elsewhere. A 2022 review says it was awarded Orphan Drug Designation in 2001 by the US FDA for acute respiratory distress syndrome, and for pulmonary arterial hypertension in 2005. The same review says it got approved for human trials by FDA in 2001, which is permission to test a drug rather than to sell it.

Question 15

What else is VIP studied for?

Accepted Answer

Three other lines run through this literature, and all three measure the body's own VIP. The first is inflammation, where a 2015 study working in vitro and in mice describes VIP stimulating CD4(+) and resident innate lymphoid type 2 cells, creating an inflammatory signaling loop that promotes allergic inflammation. That is a mechanism, rather than an outcome anybody measured in a person. The second is the brain. A 2012 review calls VIP a pleiotropic peptide that combines neuroprotective and immunomodulatory actions. Pleiotropic means one molecule with many separate jobs. The third is the body clock. A 2020 review names arginine vasopressin and vasoactive intestinal peptide as the neuromodulators that changed how the clock is understood. Only inflammation has since gained a human reading from a dose, in a COVID-19 infusion trial that reported reduced interleukin 6 cytokine release, and the other two lines remain laboratory and review work among the sources cited on this page.

Question 16

How is VIP thought to work?

Accepted Answer

Through its own receptors, and then through a single internal messenger. A 2001 review states the step plainly: the VIP peptide combines with its receptor and dose-dependently activates adenylyl cyclase. Adenylyl cyclase makes cyclic AMP, the internal signal that tells a muscle cell to relax. That is why the effects look so similar in such different places. A gut wall, an airway and a coronary artery all relax through the same chemistry. The receptor has a name worth knowing. A 2023 experiment used mouse fibroblasts engineered to express the VIP receptor (i.e., VPAC2), where VIP-induced coupling was sufficient to synchronize, and maintain, robust circadian oscillations. VPAC2 is also the receptor behind the human genetics. A 2011 study found duplications within 89 kilobases upstream of the vasoactive intestinal peptide receptor gene VIPR2 in people with schizophrenia. That is a gene finding about the receptor, and it says nothing about giving anybody the peptide.

VIP