VIP Peptide: Aviptadil, Receptors, Evidence and Safety
VIP peptide guide covering VPAC1 and VPAC2 receptors, aviptadil COVID-19 ARDS and sarcoidosis trials, Invicorp for ED, intranasal claims and short half-life.
VIP, short for vasoactive intestinal peptide, is a 28-amino-acid signaling peptide found throughout the nervous system, gut, lungs and immune tissue. Its synthetic version is called aviptadil. Online, VIP is marketed for everything from "mold illness" recovery to lung healing, but the real evidence is narrow, mixed and very dependent on route and indication.
The honest summary is that native VIP biology is well characterized, aviptadil has been studied in serious clinical conditions with mostly disappointing results, one aviptadil combination product is approved abroad for erectile dysfunction, and the popular intranasal "wellness" use is off-label and unproven. Those are different evidence tiers and should not be blended.
For related context on signaling and immune-modulating peptides, compare this guide with oxytocin, the antimicrobial peptide LL-37, KPV and BPC-157, plus the background pages on what peptides are and the peptide half-life guide. Because VIP is sometimes self-injected, the general handling concepts in how to inject peptides safely are worth reading, though they never replace a clinician.
This guide is educational and not medical advice. Aviptadil is an investigational or prescription drug depending on the country and product. It should only be used through qualified medical care.
VIP At A Glance
| Question | Evidence-aware answer |
|---|---|
| What is it? | A 28-amino-acid neuropeptide that signals through VPAC1 and VPAC2 receptors; aviptadil is the synthetic form. |
| Main native effects | Vasodilation, smooth-muscle relaxation, immune modulation, surfactant support and bronchodilation. |
| Approval status | Investigational in the US; the aviptadil-phentolamine product Invicorp is approved for ED in some European countries. |
| Best-known trials | COVID-19 respiratory failure (TESICO and others, largely negative) and a small open-label sarcoidosis study. |
| Half-life | Very short, roughly one minute in plasma, due to rapid enzymatic degradation. |
| Main safety frame | Hypotension, flushing, diarrhea and dose-limiting cardiovascular effects. |
What VIP Is
VIP was first isolated from intestine, hence the name, but it is widely distributed. It functions as a neurotransmitter and neuroendocrine mediator and participates in vasodilation, smooth-muscle relaxation in the gut and airways, secretion regulation, circadian signaling and immune control. In the lung it is associated with bronchodilation, surfactant production and anti-inflammatory effects on macrophages and monocytes.
Aviptadil is synthetic VIP with the identical 28-amino-acid sequence. When you see "aviptadil" in a trial registry or a European product label, it is the same peptide that researchers call VIP.
Mechanism: VPAC1 And VPAC2 Receptors
VIP acts mainly through two class B G-protein-coupled receptors, VPAC1 and VPAC2. Both bind VIP and the related peptide PACAP with comparable affinity, while a third receptor, PAC1, is far more selective for PACAP. Activation of VPAC receptors raises intracellular cyclic AMP, which drives downstream vasodilation, smooth-muscle relaxation and shifts in immune-cell behavior.
The IUPHAR pharmacology reviews describe these receptors in detail. VPAC1 is prominent in lung, liver and T cells; VPAC2 is found in smooth muscle, the suprachiasmatic nucleus and other tissues. This dual-receptor, cAMP-driven mechanism explains both the therapeutic hopes for VIP and its characteristic side effects. The same vasodilation that might protect lung tissue also lowers blood pressure and causes flushing.
Evidence By Area
Aviptadil For COVID-19 Respiratory Failure
The highest-profile modern use of VIP was intravenous or inhaled aviptadil for COVID-19 acute hypoxemic respiratory failure and ARDS. The rationale was aviptadil's lung-protective profile: surfactant support, reduced cytopathic effect and dampened inflammation in monocytes.
The largest rigorous test was the TESICO trial, a randomized, placebo-controlled study run across US sites that enrolled hundreds of patients with COVID-19 hypoxemic respiratory failure and gave a daily infusion of aviptadil for three days. It was published in The Lancet Respiratory Medicine in 2023 and was a negative trial; aviptadil did not deliver the hoped-for benefit. An accompanying editorial summarized it bluntly as a negative trial for vasoactive intestinal peptide. A separate 60-day randomized controlled trial in critically ill COVID-19 patients reported some signals but did not establish aviptadil as an effective therapy, and the inhaled approach was studied under its own protocol.
The cautious reading: despite biologically plausible mechanisms and emergency attention during the pandemic, well-designed randomized evidence did not support aviptadil for COVID-19 respiratory failure.
Inhaled VIP For Sarcoidosis
A small open-label phase II study treated 20 patients with active pulmonary sarcoidosis using nebulized synthetic VIP (aviptadil) 50 micrograms four times daily for four weeks. Inhaled VIP was safe and well tolerated and reduced production of tumor necrosis factor-alpha by cells from bronchoalveolar lavage, with increases in regulatory T cells. This is a mechanistic, immunoregulatory signal in a tiny uncontrolled study, not proof of clinical benefit.
Aviptadil-Phentolamine For Erectile Dysfunction
The one setting where a VIP-based product has formal approval is erectile dysfunction. Invicorp combines aviptadil 25 micrograms with phentolamine mesilate 2 mg in a single intracavernosal injection and is approved in several European countries, including the United Kingdom, Denmark and others. VIP acts mainly on the veno-occlusive mechanism while phentolamine improves arterial inflow. Reported advantages include efficacy in men who failed other therapies and a low rate of penile pain and priapism compared with prostaglandin injection. This product is not FDA approved in the United States.
Intranasal VIP And CIRS Or "Mold Illness"
Intranasal VIP is widely promoted in chronic inflammatory response syndrome (CIRS) and "mold illness" communities, often as part of a multi-step protocol. This use is off-label and unproven. There is no published randomized controlled trial demonstrating that intranasal VIP treats CIRS, mold-related illness or the broad symptom clusters described in those frameworks. Given VIP's roughly one-minute plasma half-life, the pharmacology of an intranasal "maintenance" strategy is also not well established. Anyone evaluating this use should treat it as experimental, not evidence-based.
Half-Life And Why Route Matters
VIP is degraded very quickly. Classic human pharmacokinetic work reported that plasma VIP fell by first-order kinetics with a disappearance half-time of about one minute after infusions stopped. Enzymes including neutral endopeptidase and mast-cell proteases break it down rapidly. This is why serious clinical protocols use continuous intravenous infusion or repeated nebulized dosing rather than a single shot, and it is why claims of durable systemic effects from brief exposure deserve scrutiny.
Safety
VIP's vasodilatory mechanism drives its main adverse effects.
| Safety issue | Why it matters |
|---|---|
| Hypotension | VIP is a potent vasodilator; blood-pressure drops can be dose-limiting, especially intravenously. |
| Flushing and warmth | Cutaneous vasodilation is common and expected. |
| Diarrhea | VIP affects gut secretion and motility; pathologic VIP excess (VIPoma) causes severe watery diarrhea. |
| Tachycardia and palpitations | Reflex cardiovascular responses can accompany vasodilation. |
| Injection-site or route-specific effects | Intracavernosal and inhaled routes carry their own local considerations. |
| Unknown long-term off-label safety | Intranasal and self-administered "wellness" use has no controlled safety data. |
The VIPoma syndrome, in which a tumor secretes excess VIP, is a useful natural illustration of what too much VIP signaling does: profuse watery diarrhea, low potassium and dehydration. That underlines why VIP is a powerful signaling molecule, not a benign supplement.
How To Evaluate A VIP Claim
Ask five questions.
First, which product and route is being discussed: intravenous aviptadil, inhaled aviptadil, intracavernosal Invicorp or an intranasal compounded spray? These are not interchangeable.
Second, what is the actual evidence tier? Approved (Invicorp for ED in some countries), investigational with negative trials (COVID-19 respiratory failure), small open-label signal (sarcoidosis) or unproven (intranasal CIRS use)?
Third, does the source acknowledge the negative TESICO result rather than citing only early pandemic enthusiasm?
Fourth, does it address the very short half-life and how the proposed route could plausibly deliver a sustained effect?
Fifth, does it confuse approval abroad for one product and indication with general FDA approval or general safety? That conflation is a red flag.
Bottom Line
VIP is a genuine, well-studied signaling peptide with clear receptor biology through VPAC1 and VPAC2 and real vasodilatory, immune and pulmonary effects. Its synthetic form, aviptadil, has been tested seriously in respiratory failure, where large randomized trials such as TESICO were negative, and has a small positive immunoregulatory signal in sarcoidosis. The only formally approved VIP-based product is the aviptadil-phentolamine combination Invicorp for erectile dysfunction in some European countries.
The popular intranasal use for mold illness or CIRS is off-label and unproven, and VIP's roughly one-minute half-life and potent cardiovascular effects mean it is not a casual wellness peptide. Match the claim to the specific product, route, indication and evidence tier before trusting it.
References
Harmar AJ, et al. Pharmacology and functions of receptors for VIP and PACAP: IUPHAR Review 1. Br J Pharmacol.
Couvineau A, Laburthe M. VPAC receptors: structure, molecular pharmacology and interaction with accessory proteins. Br J Pharmacol.
Brown SM, et al. Intravenous aviptadil and remdesivir for COVID-19-associated hypoxaemic respiratory failure in the USA (TESICO): a randomised, placebo-controlled trial. Lancet Respir Med. 2023.
A negative trial for vasoactive intestinal peptide in COVID-19-associated acute hypoxaemic respiratory failure. Lancet Respir Med. 2023.
Youssef JG, et al. 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. 2022.
Prasse A, et al. Inhaled Vasoactive Intestinal Peptide Exerts Immunoregulatory Effects in Sarcoidosis. Am J Respir Crit Care Med. 2010.
Dinsmore WW, Wyllie MG. Vasoactive intestinal polypeptide/phentolamine for intracavernosal injection in erectile dysfunction. BJU Int. 2008.
Domschke S, et al. Vasoactive intestinal peptide in man: pharmacokinetics, metabolic and circulatory effects. Gut. 1978.
Moody TW, et al. Therapeutic potential of vasoactive intestinal peptide and its receptors in neurological disorders.