What Are 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.
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.
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.
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.
What are the four phases of clinical trials?
Clinical trials advance through four phases to test a treatment, find the appropriate dosage, and look for side effects. If, after the first three phases, researchers find a drug or other intervention to be safe and effective, the FDA approves it for clinical use and continues to monitor its effects.
- Phase I: Tests safety and side effects on a small group.
- Phase II: Expands to a larger group, focusing on effectiveness. This phase can last several years.
- Phase III: Gathers more information about safety and effectiveness, studying different populations and different dosages. If the FDA agrees that the trial results are positive, it will approve the experimental drug or device.
- Phase IV: Takes place after the FDA approves use. Effectiveness and safety are monitored in large, diverse populations.