Participant recruitment remains a major challenge in clinical research. Delays in enrolment can extend timelines, increase costs, and affect study delivery. As a result, financial incentives are often discussed as one possible way to support recruitment in randomised controlled trials.
A paper published in Medicine, Health Care and Philosophy, ‘The ethical permissibility of financial incentives’, examines whether such incentives are ethically acceptable option to stimulate recruitment in clinical trials (1). The authors argue that while modest financial incentives may be ethically acceptable, the larger incentives should generally be avoided because they may be perceived as a coercion and create the wrong motivation for participation in clinical research which could affect the medical evidence generated from the studies.
The paper clearly distinguishes between three forms of payment to research participants: reimbursement, compensation, and financial incentives. Reimbursement is intended to cover expenses incurred through participation, such as travel or parking. Compensation is intended to recognise the time, inconvenience, or burden associated with participation. Financial incentives are different, they are not offered to repay costs or acknowledge burden, but to encourage enrolment.
The discussion then turns to the concept of undue inducement. In research ethics, this is often understood narrowly as a situation in which payment leads a person to underestimate or overlook risk. The authors take a broader view. They argue that the more important concern is whether a financial offer becomes so attractive that it is difficult to refuse, even for someone who would otherwise prefer not to participate. This matters because informed consent is not simply about disclosing risks and obtaining a signature. It also depends on whether the decision to participate is genuinely voluntary. From this perspective, even when a study was reviewed by Ethics Committee and its risks are considered acceptable, a large financial incentive may still be ethically problematic if it increases the risk of coercion.
The article also considers concerns about deception and justice. Financial incentives may encourage some individuals to withhold information or misrepresent their eligibility in order to enrol, although the authors suggest that this risk is better addressed through appropriate screening procedures and other safeguards than through lower payment levels alone. Justice raises a separate concern. Larger incentives may be especially persuasive for people experiencing financial hardship, which could result in the burdens of research participation falling disproportionately on economically disadvantaged groups.
The authors also reject the view that limiting incentives is necessarily exploitative, noting that incentives are different from compensation and are not owed in the same way. Overall, the paper does not suggest that all incentives are unethical. The authors accept that small incentives may be ethically acceptable and may contribute to improved recruitment. Their concern is with incentives that become large enough to threaten voluntary consent or reinforce unjust patterns of participation. In the absence of stronger empirical evidence, they suggest that incentives should generally remain small and tentatively propose a limit of 100 euros, while acknowledging that more research is needed to define appropriate thresholds across different contexts.
At the same time, other researchers argue that financial incentives can be fair and ethically acceptable under certain conditions. In a 2021 randomised evaluation embedded within two clinical trials, Halpern and colleagues found that incentives increased enrolment in one trial but not in the other (2). They also found no evidence that incentives functioned as undue inducements by reducing sensitivity to risk, or as unjust inducements by disproportionately attracting financially worse-off participants. Their findings suggest that current evidence does not show that financial incentives are inherently unethical, and that their effect depends on trial context rather than payment alone.
A qualitative study conducted in 2022 by Largent and colleagues adds an important participant perspective (3). Many participants described payment as one reason for joining a study, but their accounts generally did not suggest undue influence or unjust inducement. Instead, they often described payment as one practical factor among several, alongside their understanding of study procedures, possible risks, time commitment, and personal circumstances. This is important because it suggests that participants are not simply passive recipients of financial offers. They continue to weigh the overall acceptability of participation. In this sense, financial incentives may influence decisions without necessarily displacing participants’ own judgement about risk and burden.
Overall, financial incentives remain an area that requires further conceptual and practical development. The current literature does not yet provide a universally accepted framework for defining what counts as an appropriate incentive across different study types, participant populations, and levels of burden or risk. A low-burden behavioural study, a registry study, and a higher-risk interventional trial may raise very different ethical questions, even where the payment amount appears similar. Future discussion should therefore move beyond the simple question of whether payment is acceptable, and focus more on how payment should be classified, justified, reviewed, and communicated across different clinical research settings.
Reference:
- Al P, Brehaut J, Gillies K, Presseau J, Yee ML, Weijer C. The ethical permissibility of financial incentives. Med Health Care Philos. 2026 Jun;29(2):535-547. doi: 10.1007/s11019-025-10315-1. Epub 2026 Jan 2. PMID: 41483034; PMCID: PMC13086693.
- Halpern SD, Chowdhury M, Bayes B, et al. Effectiveness and Ethics of Incentives for Research Participation: 2 Randomized Clinical Trials. JAMA Intern Med. 2021;181(11):1479–1488. doi:10.1001/jamainternmed.2021.5450
- Largent EA, Eriksen W, Barg FK, Greysen SR, Halpern SD. Participants’ Perspectives on Payment for Research Participation: A Qualitative Study. Ethics Hum Res. 2022 Nov;44(6):14-22. doi: 10.1002/eahr.500147. PMID: 36316972; PMCID: PMC9631331.
Author: Wai Theng Lee, Clinical Research Partnerships Manager
