Medications containing expectorants are the most effective over-the-counter treatments for lung congestion, according to Women's Health Magazine. The most common over-the-counter expectorant ingredient is a compound called guaifenesin, according to Drugs.com.
Medicines containing expectorants help to clear chest congestion by loosening mucus in the airways in the chest, explains Woman's Health Magazine. This makes it easier for normal coughing to clear the mucus from the lungs and airway and relieve the congestion. It is important to drink water when taking expectorant drugs, as sufficient hydration contributes to loosening secretions in the airway. A humidifer may also help hydrate and loosen chest congestion in combination with an expectorant such as guaifenesin.
While guaifenesin and other expectorants are effective for managing chest congestion due to acute illness, these drugs are not very useful for treating more severe lung diseases, explains the journal Respiratory Care. Guaifenesin in particular is often sold in over-the-counter formulations that include cough suppressants such as dextromethorphan; when taken in combination, these drugs can sometimes actually worsen airway obstruction due to the suppression of the cough reflex. A class of drugs known as mucokinetic agents has shown promise for treating the severe mucus congestion in the lungs typical of diseases such as cystic fibrosis.