Thyme has been used for centuries, and was even used during one of the most devastating pandemics to take place in human history. The Black Death was a plague that peaked in Europe from 1346-1353. During that time, and in other incidents of the plague thereafter, townspeople would gather to burn large bundles of thyme to ward off the disease, or carry pockets of thyme on them. Indeed, thyme does have anti-microbial properties, but we’re not warding off any plague here-just your cough. Thyme relaxes the muscles of the trachea and bronchi, and also opens up airways. The result is less coughing, and increased comfort.
^ Güllüce, M.; Sökmen, M.; Daferera, D.; Aǧar, G.; Özkan, H.; Kartal, N.; Polissiou, M.; Sökmen, A.; Şahi̇n, F. (2003). "In Vitro Antibacterial, Antifungal, and Antioxidant Activities of the Essential Oil and Methanol Extracts of Herbal Parts and Callus Cultures of Satureja hortensis L". J. Agric. Food Chem. 51 (14): 3958–3965. doi:10.1021/jf0340308. PMID 12822930.