The principal use of guaifenesin is in the treatment of coughing, but the drug has numerous other uses, including medical, veterinary, and personal.

Guaifenesin is thought to act as an expectorant by increasing the volume and reducing the viscosity of secretions in the trachea and bronchi. It also stimulates the flow of respiratory tract secretions, allowing ciliary movement to carry the loosened secretions upward toward the pharynx.^[6] Thus, it may increase the efficiency of the cough reflex and facilitate removal of the secretions; however, objective evidence for this is limited and conflicting.

Treatment of coughing

A Cochrane Collaboration meta-analysis of over-the-counter medicines for acute cough in children and adults found no evidence for the effectiveness of any examined drug other than guaifenesin; evidence for guaifenesin was ambiguous.^[7] Guaifenesin is sometimes combined with dextromethorphan, an antitussive.

Treatment of asthma

Guaifenesin is claimed to be effective in the treatment of the thickened bronchial mucosa characteristic of asthma.^{[citation needed]} It works by drawing water into the bronchi. The water both thins mucus and lubricates the airway, facilitating the removal of mucus by coughing. However, asthmatics should not use guaifenesin routinely.

Treatment of gout

Guaifenesin is a uricosuric, increasing excretion of uric acid from the blood serum into the urine.^[8] This fact was discovered by chance, during a survey of hypouricemia in hospital inpatients.^[9] Compared to other uricosuric drugs used to treat gout, guaifenesin is relatively mild.^{[citation needed]}

Treatment of fibromyalgia

Because of its uricosuric effect, guaifenesin was chosen in the 1990s for the experimental guaifenesin protocol – a treatment for fibromyalgia. Proponents of the guaifenesin protocol believe that it treats fibromyalgia by removing excess phosphate from the body. However, a consumer alert on the Fibromyalgia Network's website^[10] states that Dr. St. Amand's claims of guaifenesin's effects on fibromyalgia are groundless, and cites double-blind research by Robert Bennett, M.D., which found no significant differences between guaifenesin and a placebo in terms of any effect on fibromyalgia or its markers.^[11]. Of note, the study by Bennett was completed in 1995. Besides the small numbers (16 guaifenesin, 15 placebo) and failure to warn patients about the blocking effects of salicylates other flaws in the project have been fully discussed by St. Amand (project consultant) on website, fibromyalgiatreatment.com.

Guaifenesin has not been approved by the FDA for the treatment of fibromyalgia, but no other clinical studies have been reported. The protocol has been adopted by many patients because of the anecdotal evidence of success. However, a more recent paper by Z. Zhang reported twenty-three altered cytokine/chemokine levels in the plasma of 92 women with fibromyalgia and 69 family members. Results were compared to 77 controls. Of the twenty-five tested cytokines/chemokines, 23 were abnormally elevated. Ten were lowered or normalized, 9 were raised, and five remained unchanged (all significant p levels)on guaifenesin treatment. ^[12] Feng J, Zhifang Z, Li W, Shen X, Song W, Yang C, Chang F, Longmate J, Marek C, St. Amand RP, Krontis T, Shively J, Sommer SS. Missense Mutations in the MEFV Gene Are Associated with Fibromyalgia Syndrome and Correlate with Elevated IL-beta Plasma Levels. PLosOne December 2009.

Use to facilitate conception

Guaifenesin is widely used by women to facilitiate conception by thinning and increasing the amount of cervical mucus.^[13] Evidence concerning the effectiveness of this use is almost entirely anecdotal; the exception^[14] is a very small study without controls. One investigator^[15] regards guaifenesin as the simplest but least effective method of improving cervical mucus.

Following a medical article in Czech about guaifenesin in the treatment of primary dysmenorrhea,^[16] another very small but double-blind and placebo-controlled experiment^[17] found that guaifenesin reduced primary dysmenorrhea, but the effect was not significant.

Use by singers

Opera singers sometimes refer to guaifenesin as the "wonder drug" for its ability to promote secondary mucosal secretion in the respiratory system. Secondary mucus is the thinner, lubricating mucus that occurs on the vocal folds naturally when they are healthy and well hydrated. Singers use guaifenesin to improve the state of their vocal folds in extremes of humidity (very humid or very dry), after flying long distances, and during mild allergies.^[18]

Side-effects

Consumption of guaifenesin in above-normal quantities has the potential to cause side-effects. Known side-effects include nausea, vomiting, and (rarely) the formation of kidney stones of uric acid (uric acid nephrolithiasis)^[19], as well as diarrhea, constipation, and a number of other side effects, some severe.^[20] Nausea and vomiting can be reduced by taking guaifenesin with meals.^[2] The risk of forming kidney stones can be reduced by maintaining good hydration and increasing the pH of urine (see Uric acid nephrolithiasis). Rarely, severe allergic reactions may occur, including a rash or swelling of the lips or face, 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 each time one takes guaifenesin.^[21] Water helps to reduce dry mouth, chapped lips, and the risk of kidney stones, and increases the effectiveness of the drug in hydrating mucus.