Sir

Henry Greely and colleagues' Commentary (Nature 456, 702–705; 2008) is the latest in a series of expert-led deliberations on the prospects and implications of cognitive-enhancing drugs (see, for example, refs 1, 2, 3). Much of the debate on enhancement, as illustrated by the Commentary, is highly speculative and rests on assumptions that are not well grounded in evidence or experience. There are three key problematic areas.

First, efficacy — the claimed and assumed benefits are often exaggerated. Careful analysis of trial data suggests that any cognitive-enhancing effects of these drugs in healthy humans are at best modest and mixed, and at worst little better than placebo.

Second, safety — very few drugs are completely without adverse effects, especially when used chronically. In the absence of data on the long-term safety implications of these drugs, it is premature to be helping society “accept the benefits of enhancement” when the balance between risk and benefit might be much narrower than assumed.

Third, demand — there is little empirical evidence that large numbers of people will use (or are interested in using) enhancers on a routine basis. There is partial or anecdotal evidence of use in specific situations (for example, examinations), but equally, other partial or anecdotal evidence suggests considerable resistance to chronic use among the general public.

If enough positive assumptions are made about these key issues, then almost any technology can look attractive or inevitable. The speculation offered in the Commentary may be of interest to academic debates in philosophy. But what is needed is realism, based on a more sober evidence-based assessment that does not create unrealistic expectations about either the potential benefits, or the threats, to individuals and society.

See also Much ado about cognitive enhancement A medical view of potential adverse effects Recall of learned information may rely on taking drug again Patterns of drug use have varied throughout history Careful use helps me do better research, and society benefits Enhancement means a broader role for physicians