Is medical research a victim of its own success? A surprising economic analysis suggests that each new medical innovation may make the next more difficult to achieve, because patients prefer to stick with proven — though potentially inferior — treatments rather than trying something new. Good effectively becomes the enemy of great.

The finding confirms the experience of many medical researchers struggling to recruit patients for their next clinical trial. But the solution proposed by the study's authors — to pay trial participants higher stipends — makes some clinicians queasy.

The analysis¹, published this month by the National Bureau of Economic Research based in Cambridge, Massachusetts, shows that the percentage of HIV-infected men who enrolled in clinical trials plummeted immediately after a regimen of antiretroviral drugs known as HAART hit the market in 1996 (see 'The price of success'). The precipitous decline, seen in data from the Multicenter AIDS Cohort Study of around 7,000 homosexual and bisexual men in four US cities from 1984 to 2005, occurred even as federal funding for HIV research nearly doubled. HAART simply worked so well, says Anup Malani, a law professor at the University of Chicago, Illinois, and an author of the new study, that patients were no longer motivated to sign up for clinical trials as a way to gain access to better treatments.

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