I just bought a bottle of the Walgreens brand of Guaifenesin 400mg tablets for chest congestion, I seem to have some congestion left over from my summer hay fever allergy. I've never used it for pain, but I prefer the 400mg, and take it as often as I feel I need it, I took one last night and just took another one.
I have heard about it online, people using it for fibromyalgia, gout and back and neck pain, something about it releases the uric acid that causes the pain. I would definitely try it for pain in the future if I need it, just to see if it helps.
Years back I bought some Source Naturals Magnesium Malate for an older friend of mine who really couldn't afford to buy any supplements, she had fibro. She said she really noticed the difference when taking it and did finish the bottle. She had a lot of other health issues at the time, so I urged her to check with her doctor first.
Her health kept declining, she had blood pressure issues and needed heart surgery and got a pace maker implant. She was on so many meds after that, she no longer took any supplements, only what her doctors gave her. This is the product if you're interested.
https://www.vitaminshoppe.com/p/source-naturals-magnesium-malate-1250-mg-180-tablets/sr-2132