Clinical Trials FAQ

Understanding Clinical Trials

A clinical trial is a research study involving a select group of people who have volunteered to try an intervention — such as a drug or other therapy, vaccine, behavior change regimen or procedure — under close medical monitoring. The study answers researchers’ questions about the safety and/or effectiveness of the intervention. Before reaching the clinical trial stage, new interventions typically have been studied in the laboratory (in nonclinical studies) and in animals (in preclinical studies).

Below are frequently asked questions about clinical trials and observational studies. To learn about specific studies that are ongoing at Fred Hutch, visit the Clinical Trials page, where you can search by disease or other criteria and view all studies.

What are clinical trial phases?


Clinical trials for treatments and vaccines typically have four phases, each of which is designed to answer different research questions. The phases are:

  • Phase 1: Safety
  • Phase 2: Efficacy
  • Phase 3: Comparison
  • Phase 4: Post-Marketing

If an intervention is successful in one phase, it may move on to the next phase. Each successive phase typically has a greater number of participants. Sometimes two phases are combined. In a Phase 3 study, each participant is randomly assigned to one of two groups. Only one group will receive the new intervention being studied; the other will receive the standard treatment for that disease.

Observational studies, such as prevention and quality-of-life studies, do not include an intervention, so they do not follow these phases.

How do observational studies differ from clinical trials?


Observational studies do not involve an intervention. The researchers simply record certain data, often through participant questionnaires or from patients’ existing medical records. Sometimes these studies include lab tests. In observational studies, the researchers use the data to determine causality and often follow groups of individuals over time.

Who participates in clinical trials and observational studies?


Depending on the clinical trial or observational study, the participants may be people who have been diagnosed with a particular disease, are survivors of a disease, are at heightened risk of a disease or are simply healthy volunteers. Some people participate in a clinical trial because there are no standard treatments available to them or because other treatments they have tried haven’t worked. Others participate for altruistic reasons, such as to advance medical knowledge. People who volunteer for lifestyle and prevention studies may be genuinely interested in learning ways to improve their health and reduce their risk of disease.

What are the potential health benefits of participating in a clinical trial or observational study?


By participating in a clinical trial, volunteers have the chance to try a new intervention that is generally not available outside of the study. If the treatment is more effective than standard care, participants may be among the first to benefit from it. In some clinical trials and observational studies, participants gain information about their health status and health risks that they wouldn’t otherwise have access to. Some lifestyle studies include consultation with a nutritionist or exercise specialist or access to innovative strategies for smoking cessation or weight loss that may prove beneficial.

Are clinical trials safe?


Clinical trials come with certain risks. New interventions being studied in a clinical trial may or may not be as effective or safe as standard treatments and care. Indeed, in early clinical studies, the safety, side effects and effectiveness of the intervention are still being ascertained. In randomized studies, patients cannot choose which group they are assigned to; in blinded studies, patients do not know which intervention they are receiving (or, in some cases, whether they are receiving a placebo).

Many measures are taken to protect the safety of clinical trial participants, including careful study design, oversight by institutional review boards and periodic monitoring of study data by independent experts. Participants also receive close medical attention and observation. Researchers must inform participants of any new risks, benefits or side effects they discover.

What will I have to do as a clinical trial or observational study participant?


Participation in a clinical trial may involve diagnostic tests, treatments, procedures, doctor visits or hospital stays that are not part of standard care. Preventive studies may involve making changes to diet, exercise or other aspects of lifestyle. Some observational studies involve minimal effort, such as agreeing to share certain test results, maintaining a diet or exercise log, or filling out questionnaires.

Are some clinical trial participants given a placebo?


Placebos, which do not contain any known active ingredient, may be used in clinical trials, but not if it would mean putting participants at risk by denying them effective therapy. This is particularly true for cancer and other serious illnesses, where placebos are rarely used. You can find out in advance if a study you are considering might involve a placebo.

Are clinical trials covered by insurance?


Some health insurance providers will pay some or all of the costs associated with participating in a clinical trial. Most often, the study itself covers the cost of the intervention while the insurance provider pays for routine care. You can ask the study staff and your insurance provider in advance to determine which costs are likely to be covered.

How do I know if I am eligible to participate?


The descriptions of clinical trials and observational studies clearly spell out who is potentially eligible. Criteria may include age, gender, ethnicity, type and stage of disease, or other characteristics. Many studies also spell out medical conditions that may exclude a person from eligibility.

How do I enroll in a clinical trial or observational study?


Each study will specify how to enroll — such as by contacting the researchers via email or filling out an online form. The researchers will review each person’s information to determine eligibility and may ask prospective participants to come in for a screening visit or take part in a phone interview.

Are study participants paid?


Some studies pay volunteers for their participation — particularly lifestyle studies and studies that involve healthy volunteers. This will be spelled out clearly in the study description. Depending on the number of clinic visits and the duration of the study, volunteers may be paid up to a few hundred dollars upon completion of the activities.

Can participants drop out of a study?


A participant can withdraw from a clinical trial or observational study for any reason and at any time. The study team may ask to continue monitoring that person for a period of time to assess any long-term effects of the treatment received in the study.

Fred Hutch Conducts Hundreds of Trials and Studies

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Faculty & Labs

Learn about the hundreds of faculty at Fred Hutch and their groundbreaking research — all of it aimed at eliminating cancer and related diseases as causes of human suffering and death. 

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Patient Care

Many patients choose Fred Hutch because we are on the leading edge of cancer research, so we can offer you the option to take part in clinical trials that match your situation.

Dr. Rachel Isaaka


Fred Hutch has hundreds of physicians dedicated to the highest-quality patient care, and many of them are known around the world for their contribution to cancer research.