Atropine

Atropine was a chemical found in deadly nightshade, potentially poisonous both to Humans and Sensorites. A group of Humans intentionally added it to the water of the Sense Sphere, the home planet of the Sensorites. (DW: The Sensorites)

Atropine can also be used beneficially; as a medication, Humans can use it for resuscitation from cardiac arrest, among other uses.