Referring patients to clinical trials: the physician's role during and after

A patient with a difficult-to-treat condition asks a primary care physician whether a clinical trial might help. The physician sees a plausible fit and considers a referral. Then a familiar concern surfaces. If the patient enrolls, what happens to the ongoing relationship? Who manages the blood pressure medication, the annual physical, the unrelated shoulder pain? Does the patient come back after the study, or does the research site absorb the care?

These questions are not academic. They shape whether physicians refer at all. And they have clear answers grounded in federal regulation, international good clinical practice guidelines, and the operational reality of how well-run trials handle communication with the referring physician.

The short version: the referring physician does not lose the patient. The investigator (the physician running the trial at the research site) takes responsibility for trial-related medical decisions and control of the study intervention. Everything else, from comorbidities to preventive care to the ongoing therapeutic relationship, stays with the referring physician by design. Understanding how that division of labor works, and where communication typically fails, is the difference between a hesitant referral and a confident one.

What the physician's role means after a clinical trial referral

Once a patient enrolls in a clinical trial, the referring physician moves into a co-management arrangement with the investigator. The investigator holds authority over anything protocol-driven. The referring physician retains authority over everything the protocol does not touch.

In practice, the referring physician continues to manage chronic conditions, adjust non-trial medications, order routine screenings, and address new complaints unrelated to the study. Patients enrolled in trials also continue to contact their primary care physician for questions about the study, for concerns about side effects, and for reassurance during a period of clinical uncertainty. That continued contact is expected, not an intrusion on the research team.

The trial itself is not a substitute for primary care. It is a defined clinical activity layered on top of it. This framing matters because it clarifies what is actually being handed off, which is a narrow slice of decision-making related to the study intervention, rather than the patient's overall care. For a broader view of how this fits into everyday practice, see The clinician's role in expanding trial access for patients.

How regulation divides responsibility between investigator and referring physician

The division is not custom. It is codified.

Under 21 CFR 312.60, the U.S. Food and Drug Administration assigns the investigator specific duties: conducting the trial according to the investigational plan, protecting the rights and welfare of participants under the investigator's care, and controlling the investigational product. FDA guidance further clarifies that the investigator is responsible for providing reasonable medical care for medical problems arising during trial participation that are, or could be, related to the study intervention.

International Council for Harmonisation Good Clinical Practice guidelines (ICH-GCP, the global standard for how clinical trials are designed and conducted) draw the same line. All trial-related medical decisions sit with the investigator or a qualified sub-investigator. Adequate medical care for trial-related adverse events (unintended medical problems that occur during a study) also sits with the investigator.

Nothing in either framework transfers responsibility for the participant's non-trial care. Comorbidities, unrelated symptoms, routine health maintenance, and prescriptions outside the protocol remain with the physician who was already managing them. This is why a well-designed referral looks less like a handoff and more like an expansion of the care team. The referring physician is not exiting the case. The research site is entering it, with a narrow and time-limited scope. That structural reality is what makes it possible for physicians to refer patients without taking on the eligibility work themselves.

What ICH E6(R3) changed about informing the referring physician

The most consequential recent change in this area is the revision of ICH-GCP itself. ICH E6(R3), the latest version of the good clinical practice guideline, was finalized in January 2025 and took effect on July 23, 2025.

The earlier version, E6(R2), included this language: "It is recommended that the investigator inform the subject's primary physician about the subject's participation in the trial if the subject has a primary physician and if the subject agrees to the primary physician being informed."

E6(R3) replaced that with stronger phrasing: "The investigator should inform the participant's primary physician about the participant's involvement in the trial if the participant has a primary physician and agrees to the primary physician being informed."

The shift from "It is recommended that the investigator inform" to "The investigator should inform" is not cosmetic. In ICH drafting convention, "should" denotes an expectation or obligation. The default now leans toward notifying the referring physician, contingent only on the participant having one and consenting to the exchange. For physicians weighing whether they will be kept in the loop after a referral, the answer built into current international guidance is that they should be. That expectation is one part of a broader shift in how referrals are being handled, discussed further in why most HCPs never refer a patient to a clinical trial, and what is changing.

Where referral communication actually breaks down

The regulatory floor is one thing. The operational reality is another, and this is where physician skepticism is often justified.

A widely cited survey of roughly 2,000 physicians and nurses conducted by the Tufts Center for the Study of Drug Development found that nearly 30 percent of physicians and 45 percent of nurses reported never receiving any initial or follow-up contact from investigative site staff after making a referral. A higher percentage reported never receiving results after the trial ended. The same body of research found that only about 9 percent of physicians cited fear of losing patients as a reason they did not refer. The dominant barrier is not competition for the patient. It is silence after the referral.

That silence has knock-on effects. Physicians who never hear back are less likely to refer again. Patients who sense a gap between their regular physician and the research site lose confidence in the study. And medication reconciliation, adverse event awareness, and post-trial transitions all suffer when the two clinicians involved in a participant's care are not in contact. The communication gap is not a physician problem. It is a system problem, and it produces measurable downstream cost for research sites and sponsors as well, which is why the hidden cost of bad referrals for clinical research sites has become an active operational concern.

What structured post-referral communication looks like in practice

A well-run co-management arrangement replaces silence with predictable touchpoints. The pattern is straightforward and does not require additional physician workload.

On receipt of the referral, the site acknowledges it. If the patient does not qualify after pre-screening, the referring physician receives a brief note explaining why, which supports future referral decisions. On enrollment, the referring physician receives a note that includes any prohibited concomitant medications and any precautions relevant to non-trial care. During the trial, milestone updates cover key events such as significant test results, withdrawal from the study, or completion. On study close, the referring physician receives an end-of-study summary and confirmation that the participant is transitioning back to standard care under the physician's direction.

Adverse events flow both ways. Trial-related adverse events are managed by the investigator and reported through sponsor and regulatory channels, with the referring physician informed of clinically relevant events. Adverse events the referring physician observes outside the trial context are communicated back to the investigator, who assesses relatedness and updates the trial record.

None of this is exotic. It is what good clinical practice already implies. The barrier has historically been infrastructure. Referral tracking, secure messaging, and closed-loop status updates are now increasingly handled through dedicated platforms designed for this exact workflow, which is one reason pre-screening platforms have become central to how HCPs connect patients to research.

How DecenTrialz supports referring physicians through the trial

DecenTrialz is built around the reality that a referral is the beginning of a relationship, not the end of one. The platform uses AI-assisted participant matching to identify potentially eligible trials, and a registered nurse conducts an initial pre-screening review before any information reaches the research site. Final eligibility determination, informed consent, study walk-through, and enrollment remain with the research site team, and the nurse does not walk participants through study details or handle consent.

For referring physicians, this structure produces a specific benefit. The physician contributes what only the physician can contribute, which is clinical judgment about whether a trial is worth exploring for a given patient. The eligibility work, the scheduling, and the follow-through with the research site are handled outside the practice. And the communication loop back to the referring physician is a feature of the workflow rather than an afterthought. Physicians who want to learn more about how the referral pathway is structured for practical use can visit decentrialz.com.

Staying the patient's physician, before, during, and after the trial

The concern that opens most physician conversations about clinical trial referrals, the worry about losing the patient, is answered by how the system is actually built. Regulation returns the patient to the referring physician for all non-trial care by design. International guidelines now expect the investigator to keep the referring physician informed. And modern referral infrastructure exists specifically to close the communication gap that has historically undermined confidence in the process.

A referral is not a transfer. It is an addition to the care team, with a defined scope and a defined end. Physicians who understand the co-management framework are positioned to offer more of their patients access to research without giving up the continuity that makes primary care effective in the first place. To see how DecenTrialz supports that relationship from referral through post-study transition, visit decentrialz.com.