What is a clinical trial?

A clinical trial is a research study that tests ways to prevent, detect, diagnose, or treat disease in people.

What do trial phases mean?

Trial phases describe the main goal of a study. Early phases often focus more on safety and dose, while later phases often study effectiveness and compare new options with current standard care.

How do I know if I am eligible?

Eligibility depends on inclusion and exclusion criteria such as diagnosis, stage, prior treatment, age, organ function, general health, and other study-specific requirements.

Do clinical trials cost money?

Costs vary by study. Some study-related costs may be covered by the sponsor, while routine care, insurance costs, travel, or lodging may not be covered in the same way in every trial.

Where can I search for clinical trials?

Patients can search the National Cancer Institute trial finder for cancer studies and ClinicalTrials.gov for a broader registry of clinical research studies and their results.

Clinical Trials: How They Work

Q: How do clinical trials work?

Clinical trials follow a written protocol that explains the purpose of the study, who can join, what treatment or procedures are used, how safety is monitored, and what data will be collected.

Clinical Trials: How They Work, Phases, Eligibility & How to Find One

Clinical trials are research studies involving people that are designed to answer specific questions about medical care, including treatment, prevention, screening, supportive care, and quality of life. In addition, they may provide patients and families with access to carefully monitored treatment options. At the same time, they help researchers understand what works, for whom, and how safely. Furthermore, the NCI explains that cancer clinical trials follow strict rules about eligibility, study conduct, and participant safety.

What Clinical Trials Are

Clinical trials are structured medical research studies that involve volunteers. In cancer care, they may test new treatments, new combinations of existing treatments, different dosing schedules, symptom management approaches, or ways to improve supportive care and quality of life. In addition, ClinicalTrials.gov describes clinical trials as research designed to learn about health and disease in general. Meanwhile, the NCI focuses more specifically on cancer-related trials and patient participation.

Why people consider them

Patients may consider a clinical trial because it can offer additional treatment options, access to new approaches, closer monitoring, or an opportunity to contribute to improved care for future patients. However, participation is voluntary, and therefore it remains a personal decision. In addition, it should be based on a clear understanding of the study’s purpose, requirements, possible risks, and potential benefits.

How Clinical Trials Work

Clinical trials follow a written plan called a protocol. In addition, the protocol explains the study’s purpose, who can participate, what tests and treatments are involved, how participants are assigned, what outcomes are being measured, and how safety is monitored. Furthermore, NCI patient guidance notes that pre-screening may come first, followed by eligibility review and, if appropriate, informed consent.

Important trial terms to explain simply

Protocol: the full study plan used to guide a clinical trial.
Eligibility criteria: the rules that determine who can and cannot join the study.
Screening: tests or review steps used to assess whether a participant qualifies.
Randomization: assignment by chance in some studies to reduce bias.
Placebo: an inactive comparison used in certain trials, which is not a substitute for effective cancer treatment when one is available.

What patients can expect

If someone is interested in a clinical trial, the usual process is to identify a study, review basic eligibility, contact the study team, and then go through screening. In addition, participants typically discuss informed consent before making a decision about enrollment. Even after joining, participation remains voluntary, and therefore patients can usually leave a study at any time.

Phases of Clinical Trials

Clinical Trials

Phases

Phase 1

Safety, dose, and administration

First-in-human studies focusing on safety, side effects, and how the treatment should be given.

Phase 2

Early effectiveness

Evaluates whether the treatment shows activity for a specific condition while continuing safety monitoring.

Phase 3

Comparison with standard care

Compares the new treatment against current standard options to assess benefit and safety.

Phase 4

Post-approval monitoring

Evaluates long-term safety and real-world effectiveness after regulatory approval.

Simple user-facing explanation

Plain-Language Summary

Phase 1

Researchers look at whether it is safe and what dose makes sense.

Phase 2

They evaluate whether it seems to work for the disease while continuing safety monitoring.

Phase 3

They compare it with current standard care to see whether it is better, similar, or safer.

Phase 4

They study what is learned after approval in broader real-world use.

Eligibility

Eligibility criteria are the rules that determine who can join a clinical trial. In addition, they may include disease type, stage, biomarkers, past treatments, age, lab values, organ function, other medical conditions, and timing since prior therapy. Furthermore, NCI guidance emphasizes that meeting these eligibility criteria is essential for identifying a suitable study.

Why eligibility rules matter

Eligibility criteria are not just administrative rules. Instead, they help protect participants, ensure the study can answer its research question clearly, and support fair interpretation of results. In addition, they improve overall study safety and reliability. As a result, a person may qualify for one trial but not another because each study is designed to answer different questions.

Common information patients may need when searching

Key Information for Clinical Trial Evaluation

Exact diagnosis
Stage or extent of disease
Pathology details
Biomarker or mutation results (if relevant)

Treatments already received
Current medications
Recent scans or lab results

Risks and Benefits

Clinical trials can have potential benefits, but they also involve uncertainties.

Clinical Trials: Benefits, Risks, and Perspective

Possible Benefits

Access to promising treatment, close monitoring, contribution to research, and potential improvement in future care — but none are guaranteed.

Possible Risks

Side effects, travel and time burden, extra tests, and the possibility that treatment may not work or may be less effective than standard care.

Balanced Perspective

A clinical trial is not automatically better or only a last resort — it may be considered early or later depending on diagnosis, timing, and treatment options.

Costs and Insurance Questions

Trial costs are often divided into routine patient care costs and research-related costs. In addition, the NCI explains that some costs may be covered by the study sponsor, some by insurance when available, and sometimes by the patient, depending on the study and specific services involved. Therefore, patients should ask the study coordinator exactly which costs are covered and which are not before joining.

Where to Search for Clinical Trials

For cancer-specific studies, the National Cancer Institute’s trial search is a strong starting point. In addition, for broader medical studies across cancer and other diseases, ClinicalTrials.gov serves as the main public registry and database. Furthermore, NCI also provides a step-by-step guide to help patients gather diagnosis details and compare them with eligibility criteria.

Best search pathways to put on page →

For cancer trials
National Cancer Institute trial search
Your oncology center or academic cancer center
Your treating oncologist or navigator

For cancer and other diseases

ClinicalTrials.gov, which covers a wide range of diseases and interventions and includes study records, eligibility details, locations, and contact information.

Simple search guidance

When searching, patients usually get better results if they know:

diagnosis name
stage or disease subtype
biomarker results
current location
treatment history
whether they want interventional treatment trials, supportive care trials, or other research types

Questions to Ask Before Joining a Trial

What is the goal of this trial?
Why do researchers think this approach may help?
What phase is the trial in?
Why do I qualify, or why might I not qualify?
What tests, visits, or extra procedures are required?
What are the possible risks and side effects?
What are the possible benefits?
What treatment would I get if I do not join this trial?
Which costs are covered, and which might I have to pay?
How often will I need to travel?
Can I leave the trial later if I change my mind?

FAQ

What are clinical trials?

Clinical trials are research studies involving people that test medical approaches such as treatments, prevention, screening, or supportive care.

How do clinical trials work?

Clinical trials follow a protocol that explains who can join, what will happen, what outcomes are measured, and how safety is monitored. Some include screening, randomization, and ongoing follow-up.

What do clinical trial phases mean?

Phase 1 usually focuses on safety and dose, phase 2 looks more at whether the treatment works, phase 3 compares it with standard treatment, and phase 4 studies use after approval.

How do I find cancer clinical trials?

A strong starting point is the National Cancer Institute’s cancer clinical trial search. Your oncology team can also help identify options that match your diagnosis and treatment history.

Where can I search for trials for cancer and other diseases?

ClinicalTrials.gov is a public registry and database that covers clinical studies for cancer and many other diseases.

Will insurance pay for clinical trials?

Coverage varies. Some costs may be covered by the sponsor, some by insurance, and some may be out of pocket, depending on the study and the service involved.

Clinical Trials:

Medical Disclaimer & Source References
© BEIJING BIOTECH.
Clinical Sources: NCCN, ASCO, ACS, ESMO, CSCO, CACA, ChiCTR.
Clinical Trials: Trial eligibility depends on diagnosis, stage, prior treatment, organ function, timing, and protocol criteria. Enrollment is not guaranteed.