Atropine was a chemical found in Atropa belladonna, potentially poisonous both to humans and Sensorites. According to the First Doctor, its symptoms included dilation of the blood vessels, high temperature and pulse rate, and a dry mouth and throat.
A group of humans intentionally added it to the water supply of Sense Sphere, the home planet of the Sensorites. However, the Doctor provided a cure to the poisoning that plagued the species. (TV: The Sensorites)