Background: Underenrollment and selective enrollment plague many clinical trials. Little is known about why hypertensive patients agree or refuse to participate in placebo-controlled trials (PCT) of antihypertensive drugs, whether the prospect of receiving placebo influences willingness to participate (WTP), or whether patients who participate differ from those who do not.
Methods: We described a hypothetical PCT of a new antihypertensive drug to 126 patients who would be eligible for ongoing phase III trials. We solicited patient motivations and concerns regarding trial participation by using open-ended questions, assessed the patients' stated WTP, and used logistic regression to determine patient characteristics associated with WTP. We reassessed WTP in 62 patients after revealing, in random order, that 10%, 30%, and 50% of patients would receive placebo.
Results: The most commonly cited motivations for participating included personal health benefits (40%), helping other patients (37%), and contributing to scientific knowledge (15%). The most common concerns were having to stop current medications (56%), inconvenience/annoyance (38%), fear of known side effects (35%), and the possibility of receiving placebo (24%). Overall, 47% of patients (95% confidence interval, 38% to 56%) were willing to participate. Younger patients (57% versus 37%; P =.01), nonsmokers (50% versus 24%; P =.04), and patients who had participated in research previously (77% versus 20%; P =.009) were all significantly more willing to participate. Fewer patients were willing to participate as the percentage who would receive placebo increased (P =.02), but randomly assigning fully half of patients to placebo still yielded maximal recruitment efficiency.
Conclusions: Hypertensive patients participate in trials for altruistic and personal health reasons. Differences between patients who do or do not participate may influence trial outcomes. The proportion of patients receiving placebo influences some patients' enrollment decisions but is not a key determinant of recruitment efficiency.