Does Guaifenesin work for fibromyalgia and not for chronic myofascial pain? I just got done looking at all the fibromyalgia medications and ratings that people put on them along with comments and I was absolutely amazed how many people reported a benefit. I take guaifenesin OTC and a cheap brand because I am disabled (without benefits) and I have not ever noticed it helping my pain levels. If anyone knows the secret recipe, please share!!