Guaifenesin, sold under the brand name Mucinex among others, is a medication used to try to help cough out phlegm from the airways. It is unclear if it decreases coughing. Guaifenesin Crystalline Powder is a medication used to treat coughs and congestion caused by the common cold, bronchitis, and other respiratory illnesses. It works by thinning and loosening mucus in the airways, making it easier to cough up. This powder is commonly used in cough syrups, tablets, and capsules. It is also used in veterinary medicine to treat respiratory conditions in animals. Guaifenesin Crystalline Powder is a safe and effective medication that can provide relief from cough and congestion symptoms.