Study Overview: This study is looking at the safety and effectiveness of a nasal spray called OPN-375 in teenagers (12-17 years old) with bilateral nasal polyps. Nasal polyps are small, non-cancerous lumps inside the nose that can cause stuffiness and breathing problems. The study will last for a total of 28 weeks. For the first 16 weeks, participants will be randomly placed into groups to receive either the OPN-375 spray or a placebo (a spray with no medicine) without knowing which one they are getting. In the final 12 weeks, everyone will receive the OPN-375 spray.

Eligibility: To join, participants need to have nasal polyps in both nostrils and should be able to stop using other nasal medicines during the study. They must also be able to fill out a daily diary and use the study's nasal spray device correctly.

• The study lasts 28 weeks in total: 16 weeks of testing and 12 weeks of open-label treatment.
• Participants are required to stop other nasal medications during the study.
• Participants will need to visit the study center multiple times for check-ups and assessments.