Types of Studies

Phase I

The main goal of Phase I studies is to learn about an experimental, or new drug's safety. This first phase of testing in humans is done in about 20 to 100 healthy volunteers, who are usually paid for being in the study. The study is planned to find out what happens to the drug in the human body (how it is taken into the body, broken down by the body, and leaves the body). A Phase I study looks at the side effects that happen when doses of the drug are increased. Phase I studies last a few months. About 70 percent of experimental drugs pass Phase I.

Phase II

Once a drug is proven to be safe, it must be tested for efficacy, or its ability to produce an effect, which is the goal of Phase II studies. These studies could last a few months, to as long as two years. They include more than a few hundred patients.

Most phase II studies are randomized trials, trials where patients do not know what drug they received. One group of patients, treatment group, will receive the experimental drug, while a second group, control group, will receive a standard treatment known as a placebo. A lot of the time, these studies are blinded, which means that neither the patients nor the researchers know who received the experimental drug. The study can provide the drug company and the FDA results about the safety and efficacy of the new drug when compared to the standard treatment used. Only about one-third of experimental drugs complete both Phase I and Phase II studies successfully.

Phase III

In a Phase III study, a drug is tested in up to more than a few hundred or thousand patients.  This large patient group gives the drug company and the FDA a better idea about the drug’s ability to work, its benefits, and the likely adverse reactions, or undesirable effects.  Most Phase III studies are randomized and blinded trials.

Phase III studies last for more than a few years.  Seventy to 90 percent of drugs that enter Phase III studies complete them successfully.  Once a Phase III study is successful, a drug company can request FDA approval to market and sell the drug.

Phase IV

In late Phase III/Phase IV studies, drug companies have a few objectives. The objectives include:

1. To compare a drug with other drugs already on the market;
2. To monitor the long-term effects of a drug, and its impact on a patient's quality of life; and
3. To determine how cost-effective the drug is when compared to other standard and new treatments.