Clinical research that is related to developing products for patient care is divided into two preclinical and four clinical phases, each addressing different questions. The knowledge gained at each phase is assessed before progressing to the next. The table below provides an overview of the process. Click each phase to learn more.

Once a safe dose has been established and the pharmacokinetics of the drug are understood, Phase II studies begin. Like Phase I studies, Phase II studies enroll small numbers of subjects, usually a few hundred. However, these subjects have the disease or condition being studied.

The most effective way to demonstrate what a drug can do is to give one group of subjects the drug and another group a placebo. A placebo is a substance that looks like the drug being studied but is not therapeutically active. Subjects do not always know which group they are in, and the effects of the drug on each group are statistically measured against each other. However, placebo control groups are not always used. For example, it would be unethical not to treat a cancer patient or to use a placebo in an anesthetic study. In such cases, an active control is used. An active control is a drug that has therapeutic activity in the disease or condition being studied. Therefore, an appropriate cancer chemotherapeutic agent would be given to a control group in a study of a cancer drug.

Phase II studies ask the questions:

• Is the drug effective within the safe dose range established by the Phase I studies?
• If so, is it as effective as desired by the sponsor?
• What is the minimum effective dose?
• Is the drug effective in mild, moderate, and severe cases of the disease or condition?
• Is the drug effective for all expected indications?
• Is the safety profile developed during Phase I upheld by the results of Phase II studies?
• Is the safety profile different in patients with the disease than healthy volunteers?