Understanding Clinical Drug Trial Phases

Phase I

The goal of a Phase I study is to find out three things:

  • How much of an experimental or investigational drug can be given safely
  • How often the drug needs to be given
  • What the side effects of the investigational drug are

Generally, if you are one of the first subjects to take part in a Phase I study, you will be given a small amount of the investigational drug. This amount is based on animal testing or the safe dose of a similar medicaiton given to other people. In some cases, it is based on the safe dose of the new drug given to peple who took part in earlier studies of the drug.

If there are no serious side effects, people who enroll later in the same study will receive more of the drug, until the study team learns the maximum amount of the drug that can be given and still be reasonably safe.  This is called "dose escalation".

About 20 to 30 people are included in Phase I studies.

Important things to know about Phase I trials

  • Because you might be one of the first people in the world to receive the investigational drug, the side effects may not be known.
  • Although the drug has shown promise in the laboratory or when used on animals, it is unknown whether it will work in humans.

Phase II

The goals of a Phase II study are to:

  • Continue to gather information about the safety of the drug
  • Test whether or not the drug works against a specific disease or condition

In Phase II studies, subjects with a specific condition or disease are given the highest dose of the new drug that is thought to be reasonably safe. This dose is based on results from Phase I studies.

Important thing to know about Phase II trials

  • When Phase II trials are conducted, researchers do not know whether or not the investigational drug will be effective

Phase III

The goal of a Phase III study is to compare the investigational drug to a standard or current drug or treatment.

Subjects in Phase III trials are often assigned at random to a group that receives standard treatment or to a group that receives the investigational drug. This means that the subject is assigned to a group by chance, like rolling dice or flipping a coin, and not by his or her doctor (this chance assignment process is called "randomization"). Sometimes in order to allow for a fair or unbiased comparison, the patient and the doctor do not even know which group the subject is in.

Sometimes there is no effective standard treatment for the subject's condition or disease. If this is the case in a Phase III trial, the investigational drug may be compared against an inactive substance called a placebo.

In Phase III studies, the investigational drug is given to hundreds or even thousands of people.

Important things to know about Phase III trials

  • If the study team learns that one of the drugs is not effective or is too toxic, the study might be changed or stopped earlier than planned.
  • At the beginning of the study, doctors do not know if the investigational drug is better than the standard treatment.

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