A well-designed clinical trial is the best way to prove a treatment or medical approach works.

In a clinical trial, participants get specific treatments or interventions based on a research plan. This is also called research protocol. Interventions can be a medical product (e.g., drug or device), a procedure (e.g., surgery) or changes to the participants’ behavior (e.g., diet or exercise).

During the trial, researchers compare a new intervention with an existing one. Or they may compare a new medicine with a “placebo.” A placebo is a medicine that appears to be like the new medicine but has no active ingredients.

A comparative study is one type of clinical trial. It looks at the differences between interventions or medicines already available. For example, it might compare one type of asthma inhaler to another.

When researchers study a new product or approach, they usually don’t know if it will be helpful, harmful or make no difference compared to other interventions. They try to determine safety and effectiveness by measuring certain outcomes in participants.

PHASE I
Purpose: Find out whether a medical approach (such as a drug, test or device) is safe, identify side effects and figure out the right doses.
Number of participants: usually fewer than 100

PHASE II
Purpose: Begin testing whether a medical approach works. Continue monitoring for side effects. Gather information for designing a large phase III trial.
Number of participants: around 100–300

PHASE III
Purpose: Prove whether a medical approach works and continue monitoring side effects.
Number of participants: as many as needed or can enroll, can be 1,000 or more

PHASE IV
Purpose: While a medical approach is being marketed, continue gathering information on its effects.
Number of people: thousands

Clinical studies are designed to add to medical knowledge related to the treatment, diagnosis and prevention of diseases. Specific reasons for studies include:

• Evaluation of one or more interventions for treating a disease, syndrome or condition
• Finding ways (medicines, vaccines or lifestyle changes) to prevent a disease or condition from developing or recurring
• Evaluating one or more methods aimed at finding or diagnosing a disease or condition
• Examining methods for identifying a condition or the risk factors for that condition
• Looking at and measuring ways to improve comfort and quality of life through supportive care

A researcher called a principal investigator (PI) leads a clinical study. They often lead a research team. This team may include doctors, nurses, social workers and other health care professionals.

Sponsors, groups or businesses usually pay for research. These might include:

• Pharmaceutical companies
• Academic medical centers
• Voluntary groups
• Nonprofit groups
• Federal agencies (like the NIH, PCORI, U.S. Department of Defense and U.S. Department of Veterans Affairs)
• Health care providers
• Other individuals

Researchers conduct clinical studies according to a research plan or protocol. The protocol answers specific research questions and ensure the health of participants.

Protocols usually include the following information:

• Reason(s) for conducting the study
• Who may take part in the study
• The number of participants needed
• A schedule of tests, procedures or drugs and their dosages
• Length of the study
• What information will be gathered about the participants

Research protocols outline who can take part in a clinical study. This is called inclusion criteria. Some researchers look for people who have the illnesses or conditions they are studying. Some studies look for healthy participants. And some studies look for a certain group of people who researchers asked to enroll.

Exclusion criteria are factors that disqualify someone from taking part in a study. Age, gender, the type and stage of a disease, prior treatment history and other existing medical conditions can be a part of inclusion and exclusion criteria.

Researchers use a process called informed consent to protect participants. Informed consent gives them detailed information about the clinical trial. This allows them to decide if they want to be part of the study. It also guides what happens if they continue with the study. Informed consent is intended to protect participants. It should give them enough information to understand the risks and benefits of taking part in the trial.

The participant must sign an informed consent document before joining a research study. This shows they received information on the risks, potential benefits and alternatives. The informed consent document is not a binding contract. Participants may withdraw from the study at any time for any reason.

An institutional review board (IRB) is a group who reviews research proposals to make sure they are ethical and protect participants. This group includes doctors, researchers, professors and members of the community. They also make sure risks are minimized and reasonable in relation to any potential benefits. The IRB reviews and approves or disapproves the research study protocol and informed consent documents.