I don't have a STD and this has never happened to me before; however, today I took a Mucinex D 1200 mg pill and approximately 3 hours later, while urinating, a mucous-like substance was dispelled from my urethra. There was no pain while urinating nor any burning sensation typically associated with a STD, and again, THIS HAS NEVER HAPPENED TO ME BEFORE. The only "X" factor was that I took mucinex today.