| I'm allergic to guaifenesen and dextromethorphan, the main active ingredients. When I was younger, I tried three different brands and vomited each time, which was how we discovered that I can't have guaifenesen. More recently, I had a headache and stuffy nose, took Tylenol Head Congestion, which has dextromethorphan in it, and got nauseous. I have been drinking a lot of water and the cough is still there. |