Disclosed is a method of treating or ameliorating a condition which can be treated or ameliorated by the administration of guaifenesin, which method comprises orally administering to a subject in need thereof an effective amount of an immediate release solution for oral administration of guaifenesin and at least one additional drug. In addition to water the solution comprises as solvents propylene glycol and glycerol in a concentration which significantly increases the bioavailability of guaifenesin in the human body.
