Why would anyone object to someone choosing to be smarter, better focused, and more productive? Surely cognitive enhancement has much to offer individuals and society, and legal dispensers of methylphenidate (Ritalin) should not object. Unfortunately, the case for healthy people taking this drug is not so straightforward. Doctors routinely decide whether to intervene based on a calculation of relative risks and benefits. Here, the risks outweigh the benefits.

Some doctors might reflexively think that the answer to the target question is an obvious “no.” After all, doctors are in the business of treating disease and not enhancing normal abilities. On scrutiny, this distinction proves to be unreliable, particularly when conditions lack clear categorical boundaries. For example, if individuals of short stature can be “treated” with growth hormone,1 …