Guaifenesin
"A few years ago I took Mucinex for a cough before going on a hike.  I noticed that after the hike I didn't hurt as much and my recovery time was much shorter.  I had bad leg and back pain at the time.  A few months ago I got  Q-Tussin for a cough.  Wow!  For the first time in years I had the desire to clean the house and I was able to.  I looked up other uses for guaifenesin and there it was - it helps with fibromyalgia.  I have since been diagnosed with fibro and I try to take the 600 mg of Mucinex twice a day.   It may not work for everyone but it makes me a functioning human being again.  I am much happier, in less pain, and my irritable bowel syndrome has cleared up."