Healthy and Sick Participants in Clinical Trials

There are multiple participants in a clinical trial. Some are healthy while the others have the disease being studied.


Their role is to help researchers find answers to specific questions outlined in a research plan, known as the protocol. It contains vital information, such as the purpose of the study, the eligibility criteria of participants, and the length of the study.


Who can participate in a clinical study?

Interested participants need to qualify and meet certain requirements for a clinical trial before they can participate.


Most trials have inclusion criteria, guidelines on who can be included in the study. They also have exclusion criteria which are guidelines of who will be excluded from the study.


Some of the criteria considered are the following:

  • Gender
  • Age
  • Type and stage of disease
  • Previous treatments
  • Other health conditions

Healthy Volunteers

Depending on the clinical study conducted, some of the participants required may need to be healthy.


Drug trials, for example, seek healthy volunteers for the Phase 0 and Phase I of the trials. Healthy volunteers are used for a dose-ranging study. This is where an agent is tested against each other to establish a dose that works best and to identify which dose is the least harmful.


The typical number of healthy volunteers for phase 1 is 20 to 100.


Healthy volunteers are vital for a variety of reasons:

  • Provide health data that can be used as a comparison
  • Help develop new knowledge, especially in medical research and development
  • Help researchers define the limits of “normal”
  • Used to match patients with certain characteristics, such as age, gender, or family relationships
  • Help investigators learn about the disease process


Healthy volunteers are given the same tests, drugs, or procedures, that a patient or sick group receives. The data gathered will provide researchers with vital information for comparison.


Sick Volunteers

Some research studies require participants with illnesses or conditions that are being studied to participate. Sick volunteers are often used in Phase II and Phase III of drug trials.


In Phase II of a drug trial, 100 to 300 patients with specific diseases are used to test a drug’s efficacy and side effects. At this stage of a drug trial, the drug is presumed not to have any therapeutic effect.


In Phase III, on the other hand, the number of patients with specific diseases are increased between 300 and 3000. A clinical researcher and personal physician will provide them with a therapeutic dose to test a drug’s efficacy, effectiveness, and safety. It is presumed that the drug has some therapeutic effect.


Many people with an illness or disease join a clinical trial to receive experimental treatment. Some of them also participate in order to get additional medical care and attention that clinical trial staff can offer.


A volunteer with a known health problem can help researchers in many ways.

  • Understand the disease or condition
  • Find better ways to diagnose the disease or condition
  • Find the ideal treatment or cure


During clinical trials, sick volunteers are advised to continue to work with their primary health care provider. Clinical staff may provide short-term procedures related to their condition but not an extended or complete primary health care.


The National Institute of Clinical Research is an SMO/CRO with offices and labs in the following cities and states: New Jersey, North Carolina, Austin, San Diego, San Francisco, Bakersfield 93309, Fountain Valley 92708, Garden Grove 92840, Hacienda Heights 91745, Huntington Beach 92648, Las Vegas 89106, Long Beach 90806, Los Angeles 90048, Ontario 91762, Rosemead 91770, San Antonio 78207, Santa Ana 92704, Upland 91786, and Westminster 92683.