Background: Paying patients to participate in clinical trials is ethically controversial. However, there has been no empirical documentation regarding whether payment represents an undue or unjust inducement.
Methods: To evaluate these questions, we described hypothetical placebo-controlled trials of a new antihypertensive drug to 126 patients with mild-to-moderate hypertension recruited from hypertension and general medicine clinics at a university hospital. Using a 3 x 3, within-subjects design, we altered a risk to participation (either adverse effect rate or rate of randomization to placebo) and the payment participants would receive ($100, $1000, and $2000) and asked patients to indicate their willingness to participate (WTP) in each trial using a 6-point scale.
Results: Clustered ordinal logistic regression models revealed that patients' WTP decreased with higher risk of adverse effects (P<.001), higher risk of being assigned to placebo (P =.02), and lower payment level (P<.001). There were no significant interactions between payment level and either risk variable, suggesting that increasing payments do not alter peoples' perceptions of risk. There was a trend toward a positive interaction between income and the influence of payment on WTP (P =.09), suggesting that payment more strongly influences WTP among wealthier people. Wealthier patients were more likely to state that payment was important in their participation decision (37% vs 20%, P =.05).
Conclusion: Although higher payment motivates research participation, we found no evidence that commonly used payment levels represent undue or unjust inducements.