Behind the scenes: Exploring the role of principal investigators (PIs) in clinical trials

The complex operations of a clinical trial require the involvement of numerous professionals, both at upper organizational levels and at clinical sites. If you are considering participating in a clinical trial, it can be helpful to know the basics about the various roles involved. You likely won’t interact with all of these people, but understanding who is in charge of what (and why) can help you feel more comfortable with the overall research process. It may also help to know that above all, the common responsibility underlying all of these positions is to ensure patient safety. A key role in clinicals trials is that of the Principal Investigator. In this article we’ll dive into what the Principal Investigator does and their main responsibilities in a clinical trial.

What does PI stand for in clinical research?

If you are participating in clinical research or are considering enrolling in a clinical trial, you may have heard the term ‘PI.’ PI stands for principal investigator, or primary investigator. The PI is the person responsible for overseeing a clinical trial, and in most cases is a qualified medical doctor with appropriate expertise to ensure the trial is conducted safely.

What does a principal investigator do?

The principal investigator is typically in charge of site management in clinical trials, or in other words, in ensuring that the trial activities are conducted according to protocol, either at individual sites or across all sites. Under a certain principal investigator definition, a trial sponsor may designate one principal investigator as the lead investigator who is responsible for coordinating multiple clinical investigators (CIs), who are each responsible for clinical trial site management at an individual study site [1].

Can a non-physician be a principal investigator?

A clinical trial principal investigator (PI) is usually a medical doctor, but it is also possible for the PI to have different qualifications – as long as a physician is appointed directly under them as a sub-investigator, who would then take on some of the PI’s responsibilities discussed here. In other words, if the PI is not a physician, then there must be a qualified physician who assumes responsibility for all trial-related medical decisions [2].

What are the responsibilities of a principal investigator in clinical research?

The principal investigator has many responsibilities in a clinical trial, and these can vary slightly between each unique trial. In general, the main responsibilities of the PI in clinical trials include the following:

Patient safety and care

The clinical trial principal investigator is first and foremost responsible for patient safety. They are present in clinical trials to ensure the necessary medical expertise is on board to keep patients safe and ensure patients are treated appropriately. The PI is usually directly involved in medical care of the patients involved in a study, ensuring that each patient receives appropriate medical care throughout the trial regardless of what group they may be assigned to or what treatment they may be receiving. The principal investigator must report adverse events to the relevant bodies and record them in the study documentation, as stipulated in the trial’s protocol.

The PI will usually be involved in the informed consent process, where participants sign the informed consent form (ICF) during enrollment to acknowledge they understand and are fully aware of all details of the clinical trial and what it implies. As a medical doctor who is also familiar with all aspects of the trial, the PI is perfectly equipped to help clarify any questions patients may have before enrolling and during the study.

Conducting the trial according to study protocol

The PI is responsible for ensuring that a trial is conducted according to the study protocol, and also in compliance with FDA regulations and Good Clinical Practice (GCP).

This includes filling out the form “FDA 1572,” the “Statement of Investigator.” We won’t get into the details of this document, but essentially it is required so as to guarantee that the PI has the necessary expertise to ensure the trial is run safely and responsibly.

Importantly, the clinical trial PI is responsible for any non-compliance, even for parts of the research that are subcontracted to contract research organizations (CROs) or other providers. Thus, even parts of the clinical trial that are outsourced to third parties are ultimately the responsibility of the PI, so you can rest easy knowing that they have chosen trustworthy partners.

Another aspect of regulatory compliance, as monitored by the PI, is validation that the study is ethical in its treatment of participants, and that any sensitive personal data is stored and processed anonymously and securely.

Clinical trial site management

Usually, the PI is in charge of clinical trial site management at one clinical research site. A given trial may involve multiple sites and would thus involve multiple PIs; one for each clinical site.

The PI oversees, either directly or indirectly, the staff members who are involved in or responsible for conducting the various trial tasks, such as in-person study visits, data collection and analysis, and patient monitoring and follow-up. The PI is also responsible for ensuring that the staff members to which such tasks are assigned are qualified and fit to perform that function.

Additional responsibilities

In addition to the responsibilities described above, the PI is also responsible for managing and controlling the supply of the drug(s) and/or other equipment/devices being studied in the trial. Further responsibilities may vary depending on the specifics of the clinical trial, including the trial phase and the logistics of the specific clinical research site and its staff team. A principal investigator may oversee multiple clinical trials simultaneously, or may also be a practicing physician seeing their regular patients alongside their duties as a PI.


The clinical trial principal investigator or primary investigator, PI, is on board amongst other investigators and trial staff members to ensure the safety of all participants and that clinical trials are conducted ethically, safely, and in line with protocol and regulations. The PI is one link among the multiple interconnected checks and balances that are in place to guarantee patient safety as the top priority in clinical research. We hope that this article has allowed you to better understand the role of the PI and how they are involved in clinical trials.