VIP and 'MCAS stacks': what's studied (aviptadil) and what's improvised

What VIP is

Vasoactive intestinal peptide is a 28-amino-acid hormone and nerve signal found in the gut, lungs, brain and blood vessels. It relaxes smooth muscle and widens blood vessels, and it has anti-inflammatory effects in some settings. Aviptadil is its synthetic drug form ¹. As of October 3, 2026, aviptadil is investigational, and Drugs@FDA holds no approved application for it ¹.

Online, VIP is sold as a nasal spray and as part of 'stacks' marketed for mast cell activation syndrome, long COVID and other inflammatory conditions. Those uses are where the evidence runs out.

Aviptadil in COVID-19: the trials

During the pandemic, VIP's effects on lung cells made aviptadil a candidate for severe COVID-19. In a 2022 trial, three days of intravenous aviptadil did not meet the primary endpoint of being alive and free of respiratory failure at day 60; survival at day 60 was better as a secondary measure, with less interleukin-6 release by day 3 (randomised trial) ².

The larger test was TESICO, a randomised trial comparing aviptadil and remdesivir with placebo in patients with COVID-19 acute hypoxaemic respiratory failure, a group whose 60-day mortality the investigators put at 30% to 50%, mostly in intensive care. Intravenous aviptadil was given as a 12-hour infusion on three days, or placebo. The trial was stopped for futility: the odds of a better day-90 outcome were 1.11, and 38% of the aviptadil group against 36% of the placebo group had died by day 90 (randomised trial) ³.

A small 2025 trial of inhaled aviptadil reported faster discharge (7.8 against 10.0 days on average), less breathlessness at day 7 and more improvement in lung scans, with deaths of 5.1% against 12.2%; the trial enrolled 80 patients at nine centres, with no drop-outs from side effects (randomised trial) ⁴. Small positive trials after a large negative one are a common pattern, and they need confirmation before they change the picture.

Where VIP has been used as a medicine

COVID-19 was not VIP's first medical outing. Combined with phentolamine as an injection into the penis, aviptadil has been used for erectile dysfunction. In a 2025 single-centre review of 308 men for whom the standard injection, alprostadil, had failed or was too painful, 59% found the aviptadil-phentolamine injection effective at three months; facial flushing affected 22.5%, and one man had priapism (retrospective study) ⁵. That use, an injection given for a local effect, says nothing about nasal sprays sold for inflammation.

Inhaled VIP has also been explored in lung disease. In an open phase 2 study, 20 people with active sarcoidosis inhaled VIP for four weeks; it was well tolerated and reduced the inflammatory signal TNF-alpha from cells washed out of their lungs, while increasing regulatory T cells (open-label study) ⁶. Without a control group, it shows biological activity in the lung, not clinical benefit, and it has not led to an approved inhaled product.

Long COVID claims

VIP is also marketed for long COVID. The only aviptadil trial we found that followed patients after hospital was the small 2025 inhaled study, which measured lung scans at day 28 in people hospitalised with COVID-19, not people with long COVID ⁴. We found no trial of VIP in long COVID. Given that the large intravenous trial in acute disease was negative ³, the long COVID claims rest on extrapolation rather than evidence.

VIP and mast cells: the opposite of the marketing

MCAS is a condition in which mast cells, immune cells that store histamine and other mediators, release them too readily, causing flushing, hives, gut symptoms and more. A treatment for MCAS should calm mast cells. VIP appears to do the reverse. In a 2008 study of human mast cells grown in the laboratory, VIP and substance P made both primary mast cells and a human mast cell line degranulate, releasing their contents, and VIP strongly induced production of inflammatory chemokines (laboratory study) ⁷.

The likely route is a receptor called MRGPRX2. A 2015 review describes it as expressed on mast cells and sensory nerves, interacting with peptides including substance P and VIP, and linked to mast cell degranulation (review) ⁸. In mice, mast cells limited the toxicity of high concentrations of VIP and of a structurally similar venom peptide by breaking them down (animal study) ⁹, another sign that VIP and mast cells are closely entangled. None of this proves that a VIP nasal spray worsens MCAS in people. It does mean the claim that VIP calms mast cells has the laboratory evidence against it.

Has VIP been tested in MCAS?

We searched PubMed on October 3, 2026 for studies of VIP in mast cell activation syndrome and found no treatment trial. MCAS itself is a field of active debate: a 2026 commentary by proponents of the broader 'consensus-2' diagnostic criteria argues that more restrictive criteria underdiagnose it and that appropriate therapy can greatly improve quality of life (commentary) ¹⁰, while other experts favour stricter criteria. Either way, treatment for MCAS is managed by clinicians who know mast cell disease, with medicines whose evidence is established for it; VIP is not among them in anything we found.

Why MCAS is easy to over-read, and to miss

Mast cell activation is common; mast cell activation syndrome is a specific diagnosis. A 2026 review of mast cell activation disorders notes that diagnosing MCAS requires elevated serum tryptase or elevated urinary mast-cell mediator metabolites and/or involvement of several organs, that mast cell activation is present in many conditions that do not qualify, and that patients are often mistaken for other conditions with similar symptoms that worsen with stress (review) ¹¹. It calls for better-defined criteria and more effective inhibitors for treatment ¹¹.

That matters for anyone drawn to peptide stacks. Symptoms labelled MCAS online may have other causes that need different treatment, and a self-diagnosis treated with an unproven peptide can delay finding them. Equally, the commentary from proponents of broader criteria argues that genuine MCAS is often missed and can be treated effectively ¹⁰. Both views point to the same practical step: assessment by a clinician who knows mast cell disease.

What 'MCAS stacks' are

Online, VIP is often sold alongside other peptides in protocols for MCAS, long COVID or chronic inflammatory illness: combinations that may include KPV, thymosin alpha-1 or BPC-157. Our encyclopedia records little or no human evidence for these in mast cell disease; KPV, for example, has no published human trial ¹. A stack of unproven peptides is not more proven than its parts, and combining them adds unknown interactions. Our blend pages explain why combinations are harder to judge than single compounds.

VIP and migraine

VIP is a potent blood-vessel dilator, and in people with migraine it can trigger attacks. In a 2021 provocation study, VIP infusion was followed by migraine attacks in 15 of 21 people against 1 of 21 on placebo, attacks resembling their usual ones, with greater headache intensity and artery widening (randomised crossover study) ¹². Anyone with migraine should know that before trying a VIP product. The related peptide PACAP behaves similarly, which our PACAP entry covers.

Status, as of October 3, 2026

Aviptadil is investigational and not FDA-approved ¹. VIP nasal sprays and injections sold online are not approved products. For athletes, VIP is not named on the WADA list, and whether S0 applies is unsettled in our tracker ¹. Our guide to 'research use only' explains what those labels do and do not mean.

If you have symptoms you think are MCAS

Flushing, hives, swelling, gut upset, palpitations and fatigue have many causes. The review of mast cell disorders stresses that the diagnosis of MCAS rests on measurable evidence, such as raised tryptase or urinary mediator metabolites, and on involvement of several organs, and that many look-alike conditions exist ¹¹. The practical route is an assessment by an allergist or immunologist familiar with mast cell disorders, ideally with tests timed to symptom flares, before any treatment is chosen. If a peptide product is already part of your routine, tell them, along with when you started it; our guide to talking to your doctor about peptides includes a script. If you have sudden swelling of the face or throat, trouble breathing or faintness, treat it as an emergency.

Questions to ask before using VIP

• Has a clinician confirmed the diagnosis, and what established treatments have been tried?
• Is there any trial of VIP in my condition? For MCAS, we found none.
• Do I have migraine? VIP can trigger attacks.
• Given that VIP activated human mast cells in the laboratory, what is the rationale for using it to calm them?
• What exactly is in the product, and is it sterile?

The bottom line

Aviptadil, the drug form of VIP, had its big test in critical COVID-19 and did not succeed; it is not approved. VIP is sold for MCAS, but no trial has tested that, and in human mast cells in the laboratory VIP triggered the very release MCAS patients want to stop. 'MCAS stacks' are improvised combinations of peptides with little human evidence. For mast cell disease, the evidence-based route runs through a clinician and established medicines.

Frequently asked questions

What is VIP peptide?

Vasoactive intestinal peptide, a 28-amino-acid hormone and nerve signal that relaxes smooth muscle and widens blood vessels. Its drug form, aviptadil, is investigational.

Did aviptadil work for COVID-19?

The largest trial, TESICO, stopped for futility, with day-90 deaths of 38% versus 36% on placebo. A smaller earlier trial missed its primary endpoint; a small inhaled trial reported faster discharge.

Does VIP help mast cell activation syndrome?

No trial has tested it. In human mast cells in the laboratory, VIP triggered degranulation, the opposite of what an MCAS treatment should do.

Can VIP cause migraines?

Yes. In a provocation study, VIP infusion triggered migraine attacks in 15 of 21 people with migraine against 1 of 21 on placebo.

Is aviptadil FDA-approved?

No. As of October 3, 2026, Drugs@FDA holds no approved application for aviptadil.

Related on Grey Peptides

• VIP (aviptadil)
• KPV
• PACAP

Sources

1. Grey Peptides encyclopedia entries for VIP (aviptadil; no approved Drugs@FDA application, read September 30, 2026; WADA unsettled) and KPV (no human trial). Read October 3, 2026.
2. Youssef, J. G., et al. (2022). The Use of IV Vasoactive Intestinal Peptide (Aviptadil) in Patients With Critical COVID-19 Respiratory Failure: Results of a 60-Day Randomized Controlled Trial. Crit Care Med, 50(11), 1545-1554. PMID: 36044317
3. Brown, S. M., et al. (2023). Intravenous aviptadil and remdesivir for treatment of COVID-19-associated hypoxaemic respiratory failure in the USA (TESICO): a randomised, placebo-controlled trial. Lancet Respir Med, 11(9), 791-803. PMID: 37348524
4. Esendagli, D., et al. (2025). Inhaled Aviptadil Is a New Hope for Recovery of Lung Damage due to COVID-19. Med Princ Pract, 34(2), 191-200. PMID: 39870064
5. Al-Mitwalli, A., et al. (2025). Intracavernosal injection of aviptadil and phentolamine for refractory erectile dysfunction. J Sex Med, 22(5), 726-730. PMID: 40192471
6. Prasse, A., et al. (2010). Inhaled vasoactive intestinal peptide exerts immunoregulatory effects in sarcoidosis. Am J Respir Crit Care Med, 182(4), 540-8. PMID: 20442436
7. Kulka, M., et al. (2008). Neuropeptides activate human mast cell degranulation and chemokine production. Immunology, 123(3), 398-410. PMID: 17922833
8. Wu, H., et al. (2015). The Origin, Expression, Function and Future Research Focus of a G Protein-coupled Receptor, Mas-related Gene X2 (MrgX2). Prog Histochem Cytochem, 50(1-2), 11-7. PMID: 26106044
9. Akahoshi, M., et al. (2011). Mast cell chymase reduces the toxicity of Gila monster venom, scorpion venom, and vasoactive intestinal polypeptide in mice. J Clin Invest, 121(10), 4180-91. PMID: 21926462
10. Afrin, L. B., et al. (2026). Progress in mast cell activation syndrome: the global consensus-2 diagnostic criteria at six years. Diagnosis (Berl), . PMID: 42240520
11. Theoharides, T. C., et al. (2026). Mast cell activation disorders: mechanisms, comorbidities and look-alike. Expert Rev Clin Immunol, 22(7), 767-787. PMID: 42405823
12. Pellesi, L., et al. (2021). Effect of Vasoactive Intestinal Polypeptide on Development of Migraine Headaches: A Randomized Clinical Trial. JAMA Netw Open, 4(8), e2118543. PMID: 34357396

Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.