Rarely, severe allergic reactions may occur, including a rash or swelling of the lips or gums, which may require urgent medical assistance. Mild dry mouth or chapped lips may also occur when taking this medication. Drinking a glass of water is recommended with each dose of guaifenesin. Pharmacology
Mechanism of action
Guaifenesin is thought to act as an expectorant by increasing the volume and reducing the viscosity of secretions in the trachea and bronchi. It may aid in the flow of respiratory tract secretions, allowing ciliary movement to carry the loosened secretions upward toward the pharynx. Thus, it may increase the efficiency of the cough reflex and facilitate removal of the secretions. Guaifenesin has muscle relaxant and anticonvulsant properties and may act as an NMDA receptor antagonist. History
Similar medicines derived from the guaiac tree were in use as a generic remedy by American indigenous peoples when explorers reached North America in the 16th century. The Spanish encountered guaiacum wood "when they conquered Santo Domingo; it was soon brought back to Europe, where it acquired an immense reputation in the sixteenth century as a cure for syphilis and certain other diseases..."The 1955 edition of the Textbook of Pharmacognosy states: "Guaiacum has a local stimulant action which is sometimes useful in sore throat. The resin is used in chronic gout and rheumatism, whilst the wood is an ingredient in the compound concentrated solution of sarsaparilla, which was formerly much used as an alternative in syphilis.
Guaifenesin was studied as a method to improve the possibility of conception, by thinning and increasing the stretchability (improved spinnbarkeit) of the cervical mucus, during the few days before ovulation, thus facilitating sperm penetration.Results from a 2014 study by the Virginia Commonwealth Universitys Department of Pediatrics indicated that guaifenesin did not have significant impact on sputum production or clearance in upper respiratory infections. This was consistent with a 2014 study involving 378 adult and adolescent participants, which indicated guaifenesin had no significant effect as either mucolytic or expectorant compared to placebo: "Although the upper respiratory quality of life improved over the course of the study in both the [guaifenesin] and placebo groups, this improvement was not accompanied by changes in sputum properties". See also
Guaiacol
Guaifenesin/phenylephrine
Methocarbamol
Mephenoxalone
Oxomemazine/guaifenesin
Plastic bronchitis

References
External links
"Guaifenesin". Drug Information Portal. U.S. National Library of Medicine. "F.D.A. Study Worries Makers of Drugs". The New York Times. 20 October 1981.