Guaifenesin, also known as glyceryl guaiacolate, is an expectorant medication taken by mouth and marketed as an aid to eliminate sputum from the respiratory tract.

[14] Although generally well-tolerated, side effects of guaifenesin may include an allergic reaction (rare), nausea, vomiting, dizziness, or headache.

[15][16] Guaifenesin might act as an expectorant by increasing the volume and reducing the viscosity of secretions in the trachea and bronchi via stimulation of the gastric mucosa.

[20] Similar medicines derived from the guaiac tree were used 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..."[21] 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.

[16] Drugs combined with guaifenesin in over-the-counter preparations include the cough-suppressant dextromethorphan, analgesics such as paracetamol/acetaminophen, and decongestants such as ephedrine, pseudoephedrine, or phenylephrine.

[28] However, results of a 2017 multicenter, placebo-controlled, repeat-dose, parallel study of 77 randomly assigned adults, suggested potential for OTC dose of oral guaifenesin 1200 mg BID to provide symptomatic relief of upper back musculoskeletal pain and spasm.