Stage 1- on diseased cells or organs to see how well the medicine affects the pathogen and cells Stage 2- on animals to see how a whole body reacts to the medicine, without risk to humans Stage 3- on a few healthy people to make sure the drug is safe and to find general side effects Stage 4- clinical trial on patients to make sure that drug works, to find the right dose and to check for side effects in different groups. A good trial tests large numbers of patients and assigns patients randomly to test a group or control group, where the control group is given the current treatment or a placebo (which looks like a medicine but contains non)