Policy recommendations for implementing registries to minimize over-volunteering in Phase I clinical trials.

Thousands of healthy volunteers enroll in Phase I clinical trials annually, often motivated by financial gain. Some engage in "over-volunteering"-participating in multiple studies simultaneously or ignoring washout periods. While serious adverse effects are rare, the experimental nature of Phase I trials, which for "first-in-human" studies are designed to trigger adverse events under controlled conditions, makes risks uncertain and unpredictable-a concern that might be compounded by concealed trial participation, which may further increase the likelihood of adverse events. Over-volunteering may also distort trial results through undetected drug interactions. To address this, France, Malaysia, and the UK have implemented national registries to track enrollments and enforce washout periods. Private, for-profit registries, like India's biometric-based system and the US-based Verified Clinical Trials, are used by some clinical research units, mostly private contract research organizations, but their use is not universal and mandatory within countries. Overall, most countries still lack mandatory systems, highlighting the need for broader oversight to protect volunteers and ensure reliable research outcomes. This article discusses the need for and barriers to implementing effective registries and argues that widespread adoption of such registries is critical to protect healthy volunteers from risk of harm while also enhancing trial results' transparency, reliability, and integrity, thereby contributing to developing safer and more effective drugs.