Clinical Trial Phases

There are different types of clinical trials depending on where a particular drug is in the clinical trial process. A new drug must pass several different clinical trials before it is submitted to the Food and Drug Administration (FDA) for approval for widespread use. Each clinical trial focuses on one particular area of the study of a drug. There are three phases of clinical trials defined by the FDA in the Code of Federal Regulations. Each phase of a clinical trial has a different purpose and helps scientists answer different questions.

Once a clinical trial is complete, the data is compiled and analyzed to determine how the drug performed. If scientists determine that a drug has been proven to be safe and effective, that drug is passed on to the next phase of clinical testing (or the FDA if all clinical trials are complete). Here are the three phases of clinical trials:

  • Phase I – these trials are conducted with a small group of people (20-80) to determine how safe a drug is. Scientists use these trials to determine the metabolism and pharmacologic actions of drugs in humans, what the side effects of the drug are with different doses, and to get some initial information on the effectiveness of the drug.

  • Phase II – these trials are conducted with a bigger group of people (100-300) to learn about the effectiveness and safety of the drug. Scientists use these trials to determine how successful a drug is in treating people with certain conditions and to see what the short-term side effects and risks of the drug may be.

  • Phase III – these trials are conducted with large groups of people (1,000-3,000) after initial trials have showed that a drug is effective. These trials help scientists confirm the effectiveness of the drug and continue to monitor side-effects. With these trials, scientists are able to compare the new drug to commonly used treatments and evaluate the overall benefit-risk relationship of the new drug. In addition to that, they also collect information that will provide a basis for physician labeling so the drug will be used safely.

For a drug or treatment to pass through the clinical trial process, it must pass through all three phases. Not until a drug has passed through Phase I trials and proven to be safe is a drug taken to Phase II and III trials. Though this may seem like a long process for a promising new drug to make it to the market, it is designed to ensure that drug treatments are safe and effective for patients.