Horehound cough drops contain natural expectorants that loosen phlegm in the throat, making it easier to cough it up, notes WebMD. The drops are made from the white horehound plant, which is also used to make many other medicines.
Horehound, which is also called bonhomme, houndsbane, marrubio blanco and many other names, is generally safe when consumed in food amounts or as a medicine, according to WebMD, but taking too much can cause vomiting.
Horehound is a wild plant that grows throughout Asia and Europe that has been used as a cough remedy since ancient Roman times, explains the University of Michigan Health System. The horehound plant contains marrubiin, the ingredient believed to cause the mucus-loosening action of horehound-based cough drops and other remedies.