I studies are to establish a drug's safety. Phase II studies are to determine whether a drug works in patients. Phase III studies evaluate a drug's action in large numbers of patients with the disease to be treated and in special patient populations. And after a drug is approved and marketed, Phase IV post-marketing studies evaluate the drug under normal use. I studies are usually conducted in 75-100 normal healthy male volunteers, recruited from a university or the community.
Potential risks are less for males than for women.
The drug's dose is gradually increased and a maximum safe level is determined. I studies last about a year. Phase II studies are designed to learn how effective the drug is against the targeted disease. These studies seek to determine an appropriate dose for the drug and the extent of any side effects. They are usually conducted in 100-500 patients and take two to five years.