Interventions aiming to slow, stop, or reverse the aging process are starting to enter clinical trials. Though this line of research is nascent, it has the potential to not only prevent prolonged human suffering, but also to extend human well-being. As this line of research develops, it is important to understand the ethical constraints of conducting such research. This paper discusses some of these constraints. In particular, it discusses the ethical difficulties of conducting this research in a way that would produce reliable data regarding the effectiveness of an anti-aging intervention. Clinical trials of such interventions, I argue, will be faced with a dilemma between two confounding variables. Eliminating the variables requires introducing ethically problematic research practices. Thus, researchers must either perform research in ethically problematic ways, or forego the conduct of high-impact clinical research on anti-aging interventions.