Methocarbamol is a central muscle relaxant for skeletal muscles, used to treat spasms. It is structurally related to guaifenesin. Methocarbamol's exact mechanism of causing skeletal muscle relaxation is unknown. It is thought to work centrally, perhaps by general depressant effects. It has no direct relaxant effects on striated muscle, nerve fibers, or the motor endplate. It will not directly relax contracted skeletal muscles. The drug has a secondary sedative effect. Methocarbamol is used for use as an adjunct to rest, physical therapy, and other measures for the relief of discomforts associated with acute, painful musculoskeletal conditions. Under the trade name Robaxin, Methocarbamol is marketed by Actient Pharmaceuticals in the United States and Pfizer in Canada.

Guaifenesin is an expectorant the action of which promotes or facilitates the removal of secretions from the respiratory tract. The precise mechanism of action of guaifenesin is not known; however, it is thought to act as an expectorant by increasing the volume and reducing the viscosity of secretions in the trachea and bronchi. In turn, this may increase the efficiency of the cough reflex and facilitate removal of the secretions. Guaifenesin is over-the-counter drug for the treatment of cough and common cold.