Review Question - QID 212700

A 26-year-old woman comes to the clinic for an annual wellness examination. She is healthy with no prior history of significant illness. She exercises 3-4 times a week and eats a plant-based diet with no carbonated drinks. When asked if anything is bothering her, she reports that she has been having recurring episodes of sneezing and congestion. She denies any fever, sick contacts, cough, headaches, chest pain, urinary symptoms, or constipation/diarrhea during these episodes. She is told to take a medication to alleviate her symptoms as needed. What is the likely mechanism of action of the medication in question?