I use grapefruit seed extract as an antifungal too. It doesnt' make my chest congestion worse.
The guaifensin is the ingredient found in Robutussin, the OTC cough syrup. I buy pills from immunesupport.com. I know that many people take this every day for months and have no problems. I researched the web and didn't find anything negative, only that it was safe so it doens't appear to be toxic in any way. I was worried about germs breeding in my lungs because my immune system is not good. I;ve had mycoplasma pnuemonia many times, so I want to avoid that if I can.So That's why I started taking this and it seems to help. I've read about others who have used it to resolve sinus infections as well as broncitis and other lung issues.