Calomel, a white, powdery chemical compound of mercury and chlorine; it is also called mercurous chloride. It has laxative and antiseptic properties, and has also been used as a treatment for intestinal worms, headaches, and nausea.

Calomel was formerly a popular ingredient in home remedies. Small doses stimulate the intestines, causing water to be retained and having a laxative effect. Because large doses of calomel can cause mercury poisoning, the drug has largely been replaced by safer compounds.

Calomel is odorless and tasteless, and cannot be dissolved in water, alcohol, or ether. When it is exposed to a great deal of sunlight, calomel changes to bichloride of mercury, a deadly poison.

Chemical formula: Hg2Cl2.