Intranasal delivery places a solution on the respiratory and olfactory epithelium of the nasal cavity, where a thin, densely vascularised mucosa allows absorption directly into systemic circulation without passing through the liver first. Total absorptive area in humans is only about 150 cm², and mucociliary clearance sweeps deposited liquid toward the pharynx within roughly fifteen to twenty minutes, so the absorption window is short.
Why the intranasal route matters in peptide research
Two properties draw researchers to it. First, avoiding first-pass metabolism raises bioavailability above oral figures for many peptides, though it remains well below subcutaneous values and is highly formulation-dependent. Second, the olfactory and trigeminal nerve pathways offer a hypothesised route to the central nervous system that circumvents the blood-brain barrier; this has been examined in animal and small human studies of oxytocin, insulin and the Russian regulatory peptides, and the evidence remains actively debated rather than settled.
Formulation is the limiting variable. Research sprays are aqueous solutions with a preservative and tonicity agent, typically delivering 50 to 100 µL per actuation, and they depend on excipient choice for stability once mixed. See our nasal spray formats, the Semax nasal spray listing and the nasal spray formulation guide.