VIPWhat the studies show

Q: What kind of evidence exists for vasoactive intestinal peptide?

Mixed evidence. A well-mapped human hormone with decades of animal and cell work, one eight-patient open-label lung study, a niche licensed use, and one large negative COVID-19 trial; nothing in people on immune or gut conditions.

A 28-amino-acid gut hormone that widens blood vessels, sets the brain's clock and calms immune cells — an approved drug in a few countries, in a tiny niche.

5 min read · Mixed evidence · Updated November 2026

In short

Name: vasoactive intestinal peptide
Evidence: Mixed evidence
Bottom line: A well-mapped human hormone with decades of animal and cell work, one eight-patient open-label lung study, a niche licensed use, and one large negative COVID-19 trial; nothing in people on immune or gut conditions.

Before you read this

This guide explains what published studies found. That is all it is.

It is not medical advice and it is not instructions for using anything. Where a dose appears, we are reporting what a named study gave the people or animals in it — a fact about the study, not an instruction to you.

The compounds here are not approved by the FDA for use in people and are sold for laboratory research only. A study tells you what happened to the subjects in it; it does not tell you what would happen to you. Talk to a doctor first.

What it is

Vasoactive intestinal peptide, or VIP, is a 28-amino-acid hormone that Sami Said and Viktor Mutt extracted from pig small intestine in 1970 and named for the first thing they saw it do: widen blood vessels ¹. It turned out to be far more than a gut hormone. Nerves throughout the body release it; it relaxes smooth muscle in the airways and gut and drives the gut to secrete fluid; and it acts through two receptors, VPAC1 and VPAC2, that sit on many immune cells as well ². Doctors see its gut effect undiluted when a rare tumour, a VIPoma, releases it without limit: the result is relentless watery diarrhoea. Few peptides have so many jobs, which is why VIP shows up in research on the immune system, the lungs, the brain's clock and the gut all at once — and why a result in one of those areas says little about the others.

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The body's clock

The brain keeps time in a cluster of neurons called the suprachiasmatic nucleus, and VIP is the signal those neurons use to stay in step with each other. In a 2005 study, clock neurons from mice lacking VIP, or lacking its VPAC2 receptor, lost their daily rhythm and drifted out of sync when recorded in a dish; applying VIP once a day restored the rhythm and pulled the cells back together ³. The mice themselves had broken sleep-wake cycles. This is some of the cleanest VIP biology there is, and it is the reason the peptide appears in the circadian-rhythm literature.

Immune cells and inflammation in mice

VIP's immune effects were worked out largely by Mario Delgado's group in Spain. In a 2001 study, mice with collagen-induced arthritis — the standard stand-in for rheumatoid arthritis — were given VIP after the disease had started; treated mice had far less joint swelling and cartilage destruction, with lower levels of the inflammatory signals TNF, IL-6 and IL-12 and a shift in T cells away from the pattern that drives autoimmunity ². The result was striking enough that VIP has been proposed for human autoimmune disease ever since, but no trial in people with an autoimmune disease has been published.

In people

VIP is cleared from blood quickly, so the human studies have given it by inhalation, by local injection or by hours-long infusion ⁴⁵⁶. In a 2003 study, eight patients with primary pulmonary hypertension inhaled VIP four times a day for three months; pressure in the pulmonary artery fell, the heart's output rose and the patients walked farther in six minutes. There was no placebo group, and eight patients cannot settle anything, but it is the study that put VIP on the map as a possible lung drug ⁴.

In a few countries VIP is an approved medicine under the name aviptadil, in one narrow use: combined with phentolamine and injected into the penis for erectile dysfunction, a product that has been licensed in Denmark and a handful of other countries ⁵.

The largest trial came during the pandemic. In the TESICO trial, run across U.S. hospitals and published in 2023, adults with COVID-19 respiratory failure were randomized to intravenous aviptadil or placebo; the drug did not improve recovery by day 90 ⁶. So the human record is a tiny open-label lung study, a niche licensed use, and one large negative trial. Nothing in people has tested VIP for immune, gut or inflammatory conditions, which is where most of the interest in it now lies.

What these studies are, and aren't

Mixed evidence. A well-mapped human hormone with decades of animal and cell work, one eight-patient open-label lung study, a niche licensed use, and one large negative COVID-19 trial; nothing in people on immune or gut conditions.