Background/Objectives: Drug-free nasal formulations may provide an alternative or adjunct to pharmacological treatment in patients with allergic rhinitis. This study in-vestigated the clinical performance, tolerability, and safety of a hypertonic nasal spray containing hydroxypropyl-β-cyclodextrin (BDNS) compared with 0.9% isotonic saline in adults with pollen-induced allergic rhinitis. Methods: This prospective, randomised, double-blind, controlled, two-period crossover study included 32 adults with pollen-induced allergic rhinitis. Participants were randomised 1:1 to receive BDNS followed by isotonic saline or the reverse sequence, with each treatment administered for 7 days. The primary endpoint was the mean Lebel Symptom Score following standard-ised nasal allergen provocation testing after each treatment period. Secondary out-comes included individual symptom scores, peak nasal inspiratory flow, nasal sensory tolerability, treatment satisfaction and preference, and safety. The primary analysis was conducted in the per-protocol set using a linear mixed-effects model. Results: All 32 randomised participants completed the study, and 30 were included in the per-protocol set. The adjusted least-squares mean Lebel Symptom Score was 3.33 after BDNS and 4.30 after isotonic saline. BDNS met the prespecified criterion for non-inferiority and subsequently demonstrated superiority over isotonic saline, with a mean treatment difference of −0.97 points in the per-protocol population (p = 0.026). The analysis in the randomised set yielded consistent findings (mean difference, −0.87 points; p = 0.033). Treatment satisfaction was significantly higher with BDNS for both perceived effectiveness (difference, 0.69; p = 0.007) and tolerability (difference, 0.81; p < 0.001). Overall, 75% of participants preferred BDNS. No serious treatment-emergent adverse events or serious adverse device effects occurred, and no device deficiencies were reported. Conclusions: In adults with pollen-induced allergic rhinitis, BDNS was non-inferior and, following hierarchical testing, superior to 0.9% isotonic saline with respect to post-provocation symptom severity after 7 days of treatment. BDNS was well tolerated and was associated with greater participant satisfaction and a clear treatment preference. These findings support the favourable short-term clinical per-formance and acceptability of BDNS under controlled allergen-challenge conditions.