A poison is a substance which, if absorbed into the body in sufficient amount results disorders in the body by chemical reactions or molecular actions.

Poisoning can be defined as the development of dose-related unpleasant effects due to exposure to the drugs, chemicals or other xenobiotics. Poisoning is one of the most common medical emergencies in many of the countries. Here are the links for articles on poisoning–
Principles of management of poisoning
Organo-phosphorus compound (OPC) poisoning
Datura poisoning