Understanding clinical trials

of potential medicines
continue to the next phase

Initial studies are most commonly conducted with a small group of healthy volunteers to help identify possible side effects and make sure the potential medicine is safe to use.

of potential medicines
continue to the next phase

Studies are conducted with a larger group of people who have a specific disease to assess if the medicine is safe, to make sure the medicine works the way it is intended and to help determine the best dose.

of potential medicines
are approved

Studies are then conducted over a longer period of time with an even larger group of people who have the specific disease. This is a very important step designed to collect enough information so that the U.S. Food and Drug Administration (FDA) can evaluate whether the medicine should be approved for use. The study closely monitors the safety and efficacy of the potential treatment.

At times, additional studies may be considered after the treatment has been approved. These trials may be used to gather more information about long-term use or to better understand the benefits and risks of medicines in a broader group of people.

Clinical trials in rare diseases

Because rare diseases often impact very small numbers of people, the FDA has created processes to allow medicines for rare diseases to follow slightly different paths:

Combining study phases, for instance,
phase I/II or II/III

Including people with the disease for phase I instead of healthy volunteers

Requiring fewer people
to participate
at each stage

Protecting participants

The FDA has many safeguards designed to protect the participants of clinical trials, and to make sure that information is shared responsibly with the broader community. These include:

Publicly stating the purpose of each trial, the exact procedures to be used, and who may or may not participate

Ensuring that the sponsors of clinical trials (the companies developing the potential medicines) do not determine – or know – who participates

Having several independent, unbiased committees review and evaluate the safety of the trial throughout the process

Ensuring the potential medicine is administered only under the supervision of qualified healthcare providers

All clinical trial participants agree to participate only after being presented with key facts about the study, including potential risks and benefits, in a process called informed consent; participants may leave a trial at any time

Making sure only qualified healthcare providers can offer medical advice, including which treatments may be appropriate

Common questions

What is a protocol?

A protocol is a set of rules to guide the clinical trial. It outlines:

  • The study objective(s)
  • Who can participate
  • The treatment dosage and procedures to be used
  • A list of information to be gathered
  • The length of the study

Who can participate?

Each trial includes “eligibility criteria.” These criteria are specific characteristics for who can and cannot participate. They can vary by trial and may include factors like age, gender, disease stage, medical history, and other treatments being used. Eligibility criteria ensure the participants are alike so the impact of the medicine can be clearly evaluated. The doctor leading the study, called the clinical investigator, determines if someone meets these criteria. The study sponsor (the company developing the medicine being researched) does not select participants.

Why would someone want to participate in a clinical trial?

Joining a clinical trial is a personal decision. Some join simply to help advance scientific research, while others may want to contribute to a better understanding of their disease. Make sure to speak with your doctor before considering participation.

Can I withdraw from a clinical trial?

Yes. Participation in a clinical trial is voluntary, and study participants can leave a trial at any time.

Does it cost money to participate?

Every study is different, but normally study-related medication and study-related medical care are provided at no cost. The study sponsor often pays for the medicine, doctor visits and in some cases any related travel.

What is informed consent?

Informed consent outlines the key facts about the study, including potential risks and benefits of the treatment. All clinical trial participants are required to read and sign a document to show they willingly agree to participate in the trial. Even with informed consent, participants can leave a trial at any time.

How can clinical trial participants learn about the study results?

Following the completion of a clinical trial, the study sponsor typically will make the results available to the general public. Study participants can also learn about the results from their doctor once the trial is over and results are shared publicly.

Where can I find more information about clinical trials?

The U.S. National Institutes of Health (NIH) has a database (ClinicalTrials.gov) available to the public with information about clinical trials around the world.