Clinical trial success depends on clean, reliable data. Yet, research shows that upwards of 10% or more of study participants may be untruthful about their concurrent enrollment in other clinical trials. These duplicate subjects—often professional patients—intentionally conceal participation at multiple sites or across sponsors.

How Duplicate Participation Increases Placebo Response

When a subject joins more than one study at the same time, the impact on trial outcomes is profound.

• Within the same trial: A subject may be randomized to placebo at one site but receive the active drug at another. This artificially boosts their reported efficacy, making the placebo look less responsive than it truly is.

• Across sponsors and indications: Subjects may simultaneously take multiple investigational products in different studies, creating unpredictable drug-drug interactions, inaccurate efficacy signals, and inflated placebo rates.

• False reporting: Many professional subjects will exaggerate or fabricate efficacy results simply to appear compliant and remain enrolled, further distorting placebo and active comparator data.

These issues directly raise placebo response rates, undermine statistical power, and can contribute to the costly failure of clinical trials.

Real-World Evidence of Impact

We have witnessed firsthand situations where investigational products with the same mechanism of action were being tested by different pharmaceutical sponsors. Sponsors that implemented the VCT system successfully met their clinical trial endpoints—while others without VCT failed. This demonstrates the clear, measurable advantage of preventing duplicate subjects in clinical trials.

The VCT Solution

By using the Verified Clinical Trials (VCT) global research subject database registry, sponsors, CROs, and sites can:

• Prevent duplicate subjects from enrolling across sites, sponsors, or therapeutic areas.

• Block professional patients from manipulating study outcomes.

• Reduce placebo response by ensuring that participants are only in one study at a time and are not simultaneously exposed to investigational products elsewhere.

• Improve data integrity and trial success by minimizing false efficacy signals and adverse event risk.

Don’t Let Hidden Risks Derail Your Study

Duplicate subjects and professional patients are the silent killers of clinical trials. They quietly erode data quality, inflate placebo rates, and jeopardize years of investment and effort. With VCT, you can expose these risks, protect your study, and maximize your probability of success.