Just want to share my experience. I felt like the mucinex caused a flare up and indeed it did. I had really gone downhill in the last few months. I thought maybe I was moving into a worse stage of my COPD. I had a bronchoscopy Friday and they found several mucus plugs that they were able to remove. I am feeling almost 100% better. The mucinex actually did cause me to get worse. My doc did not want to do a breathing test, when I first saw him because I was inflamed, so he started me on mucinex. This caused cement like mucus in my breathing filters, which was already compromised. I am extremely thankful for the broncoscopy and will now start on a regimen of mucinex daily. I honestly could barely get hardly any air into my lungs. I could barely move without my 02 dropping to 83. I am very lucky and hope this might help anyone who may have had the same symptoms as myself.