Vasoactive intestinal polypeptide (VIP) is a naturally produced neuropeptide that functions as a neuromodulator and neurotransmitter. It is a potent vasodilator, regulates smooth muscle activity, epithelial cell secretion, and blood flow in the gastrointestinal tract. As a chemical messenger, it functions as a neurohormone and paracrine mediator. Therapeutically, it is often dosed nasally in patients with mold toxicity and other biotoxin illnesses. In these patients, exogenous administration can help support healthy hormone levels, works to limit inflammation, regulates the immune system, and help in the healing activity of the brain.