I've never noticed that it made reflux any worse.
You should look up information on how it is used for Fibromyalgia. There is a doctor who believes that fibromyalgia is caused by a phosphate excretion problem. He believes that by taking guaifenesin (1200-1800mg/day), it lets your phosphate get out of the cells, where it is trapped. Supposedly, it gets rid of alot of acids.....usually through urine. But when you asked that question about reflux....it made me wonder if it, in any way, could cause more acid secretion in your stomach. I have no idea....but you could do a search on that.
I feel the same way about guaifenesin. Sometimes, it has felt like it did nothing for me. But with this blocked eustachian tube, I can hear out of the ear, if I take 1800mg a day, but not if I only take 1200.......and it gets totally bad if I stop it, so it must be doing a little something.