From 2010 to July 2021, reports that the number of registered clinical trials more than tripled, growing from 100,208 to 384,288 and counting.1

The race for a COVID-19 vaccine made clinical trials headline news in 2020 and 2021, with thousands of people worldwide volunteering to take part in vaccine studies. Still, for some, the details of what clinical trials do and how they work may not be clear.

Judy Sewards, Head of Clinical Trial Experience at Pfizer, offers some insight into the purpose, people, and phases of clinical trials.

What’s the Purpose of a Clinical Trial?

Clinical trials study whether potential new therapies are safe for humans and that they work as intended.

Some clinical trials study whether investigational therapies may help prevent disease, and others help scientists understand whether these therapies may treat disease. No matter the type of trial, Sewards says they all have one thing in common.

“Clinical trials are designed to prioritize protecting the participants,” she says. “Trials are examined by entities that provide oversight of the research study, such as institutional review boards, data and safety monitoring committees, and regulatory agencies or health authorities, to ensure it stays that way throughout the trial.”

Establishing and maintaining participants' trust is important to successfully conducting clinical trial studies, but it's just one piece of a much bigger commitment to upholding the highest ethical standards and principles in the exploration of safe and effective ways to prevent or treat diseases.. 

“Clinical trials operate from an infrastructure of ethics,” Sewards says. “You don't want to design a clinical trial that disadvantages somebody from getting standard of care treatment they’d otherwise get if they weren’t in the trial. For example, in cancer we know that patients are unlikely to benefit from a placebo so this wouldn’t generally be an option. Cancer trials typically compare the potential treatment with the existing treatment or add something new onto the existing treatment to see if the potential treatment an improve outcomes over what is available outside of the trial.”

Who are the People Involved in a Clinical Trial?

Behind every clinical trial is a team of people who keep research on track:

  • Sponsor: The person or group of people who supervise or fund the trial—such as a drug company.
  • Participant: A person who volunteers to take part in the clinical trial—such as yourself!
  • Investigator: A researcher who helps conduct the clinical trial—such as a doctor.
  • Study coordinator: A person who works with the investigator to manage the clinical trial—such as a nurse. The study coordinator usually serves as a patient’s main point of contact.

“As a participant, your primary relationship is with the study doctor, the study coordinator, and the staff who work at the site where you go to participate in the trial,” Sewards says.

What are the Phases of a Clinical Trial?

Clinical trials take place in several phases. Phase 1 helps scientists understand the safety of a particular medicine or vaccine. Phase 2 begins to understand early efficacy. Phase 3 focuses on broader efficacy and dosing in preparation for health authority approval. And Phase 4 continues to monitor and collect data after a drug has been approved. 

“Your experience in the trial can vary by phase,” Sewards says, adding that while early-phase drug trials often include healthy volunteers, late-stage research typically involves study activities for a specific health problem. “In later phases, and depending on the type of study or disease, you’re the patient—but instead of getting the current standard of care, you might receive a potential new solution.”

No matter the phase, participants can expect to be monitored throughout their participation in the study. Monitoring can take place through checkups at the research site or remotely.

Putting it All Together

Ultimately, Sewards says participating in clinical research supports the greater good. Participants can help to bring progress to science, medicine, and, in some cases, to the world at large.

“When you volunteer for a clinical trial, it’s a wonderful gift to society and something we’re all grateful for, including people that are patiently waiting for breakthroughs,” she says.

And as more people take an interest in participating in clinical trials, it also stands to make research more diverse.

“Representation across different ages, genders, races, and ethnicities in clinical trials makes a difference,” Sewards says. “The more diverse a group of clinical trial participants, the more we can learn about how a potential medicine or vaccine works within those populations. Participation in clinical trials by people of all backgrounds can make a difference by reducing health disparities among underrepresented populations and improving the development of medicines and vaccines for everyone.”

“When you participate," she says, "you’re representing people like you.”


  1. “Number of Registered Studies Over Time” Available at: Last reviewed July 23, 2021.