**Traditional knowledge approach**

This is the discovery of drugs based on traditional medical knowledge. The best example is the documented analgesic effects of extracts from opium poppy that led to the isolation of morphine from the plant and the subsequent synthesis of related analgesics.

#### **Discovery through serendipity**

This is the accidental discovery of novel drugs based on the ingenuity of a scientist investi‐ gating a problem initially unrelated to the observed phenomenon; examples of such discov‐ eries include the observation by Alexander Flemmings that penicilliummould could inhibit the growth of bacteria. This finding led to the discovery of antibiotics.

Discovery of therapeutic usefulness of a side effect e.g. clonidine originally used as a nasal decongestant was found to have antihypertensive properties while, the hypoglycemic effects of sulphonamides used in the treatment of typhoid fever led to the development of structurally related sulphonylureas as oral hypoglycemic drugs.

#### **Discovery from effects of endogenous agents in test animals**

An example of discovery arising from studies of endogenous agents in test animals is the anticoagulant action of the venom from the Malayan viper that led to the identification of the anticoagulant ancrod.

#### **Modern approaches to drug discovery**

These are those approaches that form a basis for the rational design of drugs and include the following;
