Guaifenesin is a natural product from the guaicum plant, and is used by a lot of people with FMS and CFS.
Sold in health stores with the names Guai and Guaii. Iys just that guaifenesin is extracted in a more pure concentrated form.
In the 1500s, the guaicum plant was discovered and it was found to be useful in treating "rheumatism". As recently as 1920, a study was published showing guaifenesin extracted from that plant to be an effective treatment.
I would be more concerned about marijuana addiction and the ten unknown chenicals in it.