Frequently Asked Questions:
Understanding Clinical Trials

Choosing to participate in a clinical trial is an important personal decision. Use this FAQ to be more informed.

This FAQ offers information about clinical trials, how they operate and what it means to be a trial participant. If you have additional questions, talk to your healthcare provider.

Clinical trials are generally considered to be biopharmaceutical, medical or health-related research studies that use volunteer participants to test new medicines, different combinations of existing drugs, or new devices or procedures in order to advance medical knowledge. Learn more about the clinical research process and how ideas become new medicines.

Participants in clinical trials can play a more active role in their own healthcare, gain access to new research treatments before they are widely available and help others by contributing to medical research.

All clinical trials have guidelines about who can participate. Using inclusion/exclusion criteria is an important principle of medical research that helps to produce reliable results. The factors that allow someone to participate in a clinical trial are called “inclusion criteria” and those that disallow someone from participating are called “exclusion criteria.”

These criteria are based on such factors as age, gender, the type and stage of a disease, previous treatment history, and other medical conditions. Before joining a clinical trial, a participant must qualify for the study. Some research studies seek participants with illnesses or conditions to be studied in the clinical trial, while others need healthy participants. It is important to note that inclusion and exclusion criteria are not used to reject people personally. Instead, the criteria are used to identify appropriate participants and keep them safe. The criteria help ensure that researchers will be able to answer the questions they plan to study.

Learn more about what it means to participate in a clinical trial.

The clinical trial process depends on the kind of trial being conducted (See What are the different types of clinical trials?) The clinical trial team includes doctors and nurses as well as social workers and other healthcare professionals. They determine if a person is eligible to participate in a trial, check the health of the participant at the beginning of the trial, give specific instructions for participating in the trial, monitor the participant carefully during the trial, and stay in touch after the trial is completed.

Learn more about what it means to participate in a clinical trial.

Informed consent is the process of learning the key facts about a clinical trial before deciding whether or not to participate. It is also a continuing process throughout the study to provide information for participants. To help someone decide whether or not to participate, the doctors and nurses involved in the trial explain the details of the study. If the participant’s native language is not English, translation assistance can be provided. Then the research team provides an informed consent document that includes details about the study, such as its purpose, duration, required procedures and key contacts. Risks and potential benefits are explained in the informed consent document. The participant then decides whether or not to sign the document. Informed consent is not a contract and the participant may withdraw from the trial at any time.

Every year, millions of people around the world participate in a wide range of clinical trials. Clinical trials serve a critical role—not only in the development of new drugs, but in our daily lives, too. Participants in clinical trials:

  • Play a more active role in their healthcare
  • Gain access to new research treatments before they are widely available
  • Help others by contributing to medical research that leads to the development of new treatments, medical devices or procedures

Side effects are any undesired actions or effects of the experimental drug or treatment. Negative or “adverse” effects may include headache, nausea, hair loss, skin irritation, or other physical problems. Safety is the top priority of any clinical trial and clinical trial staff monitor participants for adverse effects. Experimental treatments must be evaluated for both immediate and long-term side effects.

The ethical and legal codes that govern medical practice also apply to clinical trials. In addition, most clinical research is federally regulated with built in safeguards to protect the participants. The trial follows a carefully controlled protocol, a study plan which details what researchers will do in the study and how they will monitor patient safety. As a clinical trial progresses, researchers report the results of the trial at scientific meetings, to medical journals and to various government agencies. Individual participants’ names will remain secret and will not be mentioned in these reports (See Confidentiality Regarding Trial Participants).

People should know as much as possible about the clinical trial and feel comfortable asking the members of the healthcare team questions about the trial, the care expected while in a trial and the cost of the trial. The following questions might be helpful for the participant to discuss with the health care team. Some of the answers to these questions are found in the informed consent document.

  • What is the purpose of the study?
  • Who is going to be in the study?
  • Why do researchers believe the experimental treatment being tested may be effective? Has it been tested before?
  • What kinds of tests and experimental treatments are involved?
  • How do the possible risks, side effects, and benefits in the study compare with my current treatment?
  • How might this trial affect my daily life?
  • How long will the trial last?
  • Will hospitalization be required?
  • Who will pay for the experimental treatment?
  • Will I be reimbursed for other expenses?
  • What type of long-term follow up care is part of this study?
  • How will I know that the experimental treatment is working? Will results of the trials be provided to me?
  • Who will be in charge of my care?

  • Plan ahead and write down possible questions to ask.
  • Ask a friend or relative to come along for support and to hear the responses to the questions.
  • Bring a tape recorder to record the discussion to replay later.

Every clinical trial in the U.S. must be approved and monitored by an Institutional Review Board (IRB) to make sure the risks are as low as possible and are worth any potential benefits. An IRB is an independent committee of physicians, statisticians, community advocates, and others that ensures that a clinical trial is ethical and the rights of study participants are protected. All institutions that conduct or support biomedical research involving people must, by federal regulation, have an IRB that initially approves and periodically reviews the research.

Yes. Most clinical trials provide short-term treatments related to a designated illness or condition, but do not provide extended or complete primary healthcare. In addition, by having the healthcare provider work with the research team, the participant can ensure that other medications or treatments will not conflict with the protocol.

Yes. A participant can leave a clinical trial at any time. When withdrawing from the trial, the participant should let the research team know about such a decision and the reasons for leaving the study.

Ideas for clinical trials usually come from researchers as they understand more about our health and have ideas about how to help people live longer, healthier lives. After researchers test new therapies or procedures in the laboratory and in animal studies, the experimental treatments with the most promising laboratory results are advanced into clinical trials in humans. During a trial, more and more information is gained about an experimental treatment, its risks and how well it may or may not work.

Learn more about what it means to participate in a clinical trial.


Clinical trials are sponsored or funded by a variety of organizations or individuals such as physicians, medical institutions, foundations, voluntary groups and pharmaceutical companies, in addition to federal agencies such as the National Institutes of Health (NIH), the Department of Defense (DOD) and the Department of Veteran’s Affairs (VA). Trials can take place in a variety of locations, such as hospitals, universities, doctors’ offices, or community clinics.

A protocol is a study plan on which all clinical trials are based. The plan is carefully designed to safeguard the health of the participants as well as answer specific research questions. A protocol describes what types of people may participate in the trial; the schedule of tests, procedures, medications, and dosages; and the length of the study. While in a clinical trial, participants following a protocol are seen regularly by the research staff to monitor their health and to determine the safety and effectiveness of their treatment.

A placebo is an inactive pill, liquid, or powder that has no treatment value. In clinical trials, experimental treatments are often compared with placebos to assess the experimental treatment’s effectiveness. In some studies, the participants in the control group will receive a placebo instead of an active drug or experimental treatment.

A control is the standard by which experimental observations are evaluated. In many clinical trials, one group of patients will be given an experimental drug or treatment, while the control group is given either a standard treatment for the illness or a placebo.

As classified by the NIH, there are two main types of clinical trials: interventional and observational studies.

  • Interventional studies are those in which investigators assign participants various “interventions” (e.g., medical products, such as drugs or medical devices; specific procedures they are testing; or changes in the participant’s normal behavior) according to a pre-determined research plan, and measure the outcomes. Often, interventional studies are used to determine the safety and effectiveness of a certain drug or procedure based on these outcomes.
  • Observational studies are those in which investigators measure the outcomes of a group of participants based on their observations. While participants may receive similar interventions as part of their routine medical care, they are not assigned ones by the investigators (as is the case for interventional studies). In that sense, observation studies are more focused on learning about a key group based on observations over a specific period of time.

Clinical trials are conducted in phases. The trials at each phase have a different purpose and help clinical research scientists answer different questions:

  • In Phase I trials, researchers test an experimental drug or treatment in a small group of people (often 20-80) for the first time to evaluate its safety, determine a safe dosage range and identify side effects.
  • In Phase II trials, the experimental study drug or treatment is given to a larger group of people (often 100-300) to see if it is effective and to further evaluate its safety.
  • In Phase III trials, the experimental study drug or treatment is given to large groups of people (often 1,000-3,000 or more) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments and collect information that will allow the experimental drug or treatment to be used safely.
  • In Phase IV trials, after being approved by government regulators, post-marketing studies determine additional information including the drug’s risks, benefits, and optimal use.

Most human use of investigational new drugs takes place in controlled clinical trials conducted to assess safety and efficacy of new drugs. Data from the trials can serve as the basis for the drug marketing application. Sometimes, patients do not qualify for these carefully-controlled trials be cause of other health problems, age, or other factors. For patients who may benefit from the drug use but don’t qualify for the trials, FDA regulations enable manufacturers of investigational new drugs to provide for “expanded access” use of the drug.

For example, a treatment IND (Investigational New Drug application) or treatment protocol is a relatively unrestricted study. The primary intent of a treatment IND/protocol is to provide for access to the new drug for people with a life-threatening or serious disease for which there is no good alternative treatment. A secondary purpose for a treatment IND/protocol is to generate additional information about the drug, especially its safety. Expanded access protocols can be undertaken only if clinical investigators are actively studying the experimental treatment in well-controlled studies, or all studies have been completed. There must be evidence that the drug may be an effective treatment in patients like those to be treated under the protocol. The drug cannot expose patients to unreasonable risks given the severity of the disease to be treated.

Some investigational drugs are available from pharmaceutical manufacturers through expanded access programs listed in Expanded access protocols are generally managed by the manufacturer, with the investigational treatment administered by researchers or doctors in office-based practice. If you or a loved one are interested in treatment with an investigational drug under an expanded access protocol listed in, review the protocol eligibility criteria and location information and inquire using the Contact Information.

See “FDA Finds New Ways to Speed Treatments to Patients” for more details.

How can I participate in a clinical trial?

If you identify a trial of interest, the next step is to contact the study research staff and ask specific questions about participating.

Please note: ACRO does not conduct clinical trials and cannot provide advice about what studies may be available.

How are new drugs researched and developed?