Introduction Scholars have debated how to define coercion and undue influence, but how institutional review boards (IRBs) view and make decisions about these issues in actual cases has not been explored.

Methods I contacted the leadership of 60 US IRBs (every fourth one in the list of the top 240 institutions by National Institutes of Health funding), and interviewed 39 IRB leaders or administrators from 34 of these institutions (response rate=55%), and 7 members.

Results IRBs wrestled with defining of ‘coercion’ and ‘undue inducement’, most notably in deciding about participant compensation. IRBs often use these terms synonymously and define undue inducement in varying ways, often wrestling with these issues, relying on ‘gut feelings’, and seeking compromises. Ambiguities arose, partly reflecting underlying tensions: whether subjects should ‘get paid’ versus ‘volunteer’ (ie, whether subjects should be motivated by compensation vs altruism), and whether subjects should be paid differently based on income, given possible resultant selection bias. Lack of consistent standards emerged between and even on single IRBs. Questions arose concerning certain aspects and types of studies; for example, how to view and weigh providing free care in research, whether and how recruitment flyers should mention compensation, and how to avoid coercion in paediatric, developing world, or students research.

Conclusions These data, the first to probe qualitatively how IRBs view and approach questions about coercion, undue influence and participant compensation, and to examine how IRBs have reviewed actual cases, reveal several critical ambiguities and dilemmas, and have vital implications for future practice, education, policy and research.