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Every day, 17 Americans die while waiting for an organ transplant. Opt-out organ donation policies, which enroll everyone into post-mortem donation programs by default unless people choose to opt out, have been touted as a way to increase the supply of desperately needed organs. But opt-out organ donation policies may reduce living organ donations, leaving systems no better supplied with lifesaving organs.
Pascal Güntürkün and colleagues analyzed epidemiological data from 24 countries between 2000–2023 and conducted four experimental studies with over 5,000 participants to examine how switching from opt-in to opt-out organ donation policies affects both deceased and living donor rates. The research is published in the journal PNAS Nexus.
The authors found that while opt-out policies led to a non-significant increase in deceased donors of 1.21 people per million population, the policies significantly decreased living donors by 4.59 people per million population—a 29% reduction.
Through experiments and comparisons between Germany (opt-in) and Austria (opt-out), the authors demonstrated that this crowding-out effect primarily affects so-called “altruistic donations” to acquaintances and strangers, rather than donations to family members. People living in countries with opt-out systems perceive organ supply as sufficient, and are consequently less willing to become living donors.
According to the authors, the findings reveal the unintended consequences of a public policy nudge and suggest that policymakers should consider potential crowding-out effects when implementing opt-out organ donation systems.

Switching to an opt-out policy has a lasting negative effect on living donor rates. Results of a difference-in-differences model with staggered treatment adoption. The vertical dashed lines in panel A and B reflect the timepoint of the policy switch. Panel C shows average annual post-adoption effects. Credit: Güntürkün et al.
More information:
Pascal Güntürkün et al, Crowding-out effects of opt-out defaults: Evidence from organ donation policies, PNAS Nexus (2025). DOI: 10.1093/pnasnexus/pgaf311
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Opt-out organ donation policies may reduce organ supply (2025, October 28)
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