The Safety, Feasibility, and Repeatability of Inhaled ATP Cough Challenges

This study is testing whether inhaling a substance called ATP (a natural energy molecule found in cells) can safely trigger coughing, and whether this test can be reliably repeated — which could help doctors better study and treat chronic cough. Healthy adults are tested first, then patients with chronic cough. **You may be eligible if...** - You are 18 or older - For the first phase: you are a healthy adult with normal lung function and no history of chronic cough or breathing problems - For later phases: you have chronic cough or another respiratory condition being studied **You may NOT be eligible if...** - You are a smoker or have a significant smoking history (more than 5 pack-years within the last 6 months) - You have had a recent respiratory infection within 6 weeks - You cannot perform reliable lung function tests - You are taking certain medications that affect coughing (such as ACE inhibitors) Talk to your doctor to see if this trial is right for you.