The Importance of Healthy Volunteers in Clinical Trials

Clinical trials play a pivotal role in advancing medical research and developing new treatments. At the heart of these trials are healthy volunteers, individuals who willingly participate in clinical research to drive medical advancements. 

In this article, we explore the significance of healthy volunteers in clinical trials and their impact on drug development.

What are healthy volunteers?

Healthy volunteers are individuals who take part in clinical trials, but who are not known to suffer any condition relevant to the study [1]. They must be in good overall health and do not have any mental or physical condition that requires frequent medication. The role of healthy volunteers is crucial in contributing valuable data to researchers, helping establish broader safety parameters, dosage guidelines, and potential side effects.

Why are healthy volunteers involved in clinical trials?

The main reason behind involving healthy volunteers in clinical research is to gather a broader understanding of the development drug, determining how it generally reacts with the human body. Healthy volunteers provide a baseline for comparison, offering insights into the impact of treatments by eliminating variables present in individuals with pre-existing conditions. 

Healthy volunteers are mainly involved in phase 1 of the research process. Phases 2 and 3 then focus on volunteers with a specific condition. 

Phase 1

Phase 1 trials involve 20 to 100 healthy volunteers. In some cases, phase 1 research can involve patients with the condition under investigation. The primary objectives of this phase include establishing the safety profile of the treatment and determining the appropriate dosage. 

The emphasis on safety in phase 1 is not just a procedural step but a critical component in progressing the trial. Establishing safety parameters ensures that following phases build on a foundation of secure experimentation, safeguarding both volunteers and potential patients.

Phase 2

Phase 2 enlists several hundred volunteers with the specific condition. In this phase, researchers shift their focus to assessing the treatment’s effectiveness and side effects in subjects with the condition. Understanding the nuances of treatment effectiveness and potential side effects refines the therapeutic approach for individuals with the targeted condition.

Phase 3

In Phase 3, the research focuses on a larger cohort of 300 to 3,000 volunteers with the condition. This phase is critical for understanding the treatment’s overall effectiveness, as well as identifying potential side effects that may surface in a broader population.

Why involve 300 to 3,000 volunteers in Phase 3? The scale provides a more thorough evaluation in a more representative sample size, crucial for determining the treatment’s applicability on a broader scale, enhancing its potential for widespread use.

Phase 4

Phase 4 extends the study to include several thousand volunteers with the condition, ensuring a thorough examination of the treatment’s long-term safety and effectiveness. This phase plays a crucial role in monitoring real-world outcomes. 

What’s required from healthy volunteers?

For those contemplating participation, specific criteria must be met:

  • Good overall health
  • Meet the eligibility criteria
  • Informed consent
  • Time commitment

Good overall health

Healthy volunteers in clinical trials must demonstrate good overall health. During phase 1 trials, researchers aim to establish whether a new drug is safe and what side effects it might have. To do this, the research begins with healthy adults, usually between 18 to 55 years old. 

Any healthy volunteer that participates in the trial undergoes a health checkup from a medical professional, much like a regular checkup at the doctor’s office. Depending on the study, there might be extra checks like blood tests or heart checks with electrocardiograms. These checks create a starting point to compare how things change during the study.

Meet the eligibility criteria

Entering a clinical trial is a structured process, and meeting eligibility criteria is a fundamental step. Unlike an open invitation, participation requires individuals to fulfil specific requirements. 

These criteria, encompassing factors such as sex, age, weight, and medical history, serve as the foundation for assembling a purposeful and well-defined study group. The eligibility criteria can differ from trial to trial, and will depend on the overall aims of the study.

Informed consent

In clinical trials, informed consent is critical. It’s not just a formality; it’s a way of ensuring everyone knows what’s going on and agrees to be part of the study in a clear and transparent manner. 

The main goal of the informed consent process is to make sure participants have all the details about the study. This includes how long it will last, what they’ll be doing, and what’s expected of them. This information helps participants make informed choices about joining the trial as a healthy volunteer.

Time commitment

Participating in phase 1 clinical trials for healthy individuals involves a time commitment that varies from several days to months. The nature of these trials often requires close monitoring, sometimes leading participants to stay at the clinic for the trial’s duration. Volunteers may need to take time off from work or make arrangements with their families due to the potential duration of the trial. 

For those considering participation, volunteers may be required to travel to the clinic. However, the cost of travel is often included in the overall study compensation or is reimbursed. Additionally, decentralised trials are becoming increasingly popular; remote or flexible studies that do not rely on a centralised study site.


Clinical trials are crucial for advancing medical research and developing new treatments. The key players in this journey are the healthy volunteers—individuals willingly stepping forward to drive scientific progress. Without healthy volunteers, trails would be unable to gain a broader understanding of the drug’s safety and efficacy profile in a general population. 

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Royal College of Physicians (1986). Research on healthy subjects. J R Coll Physicians, London. 20:243–57.

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