I have been taking 50 mg of modafinil almost daily for over a year. For most of my 74 years, I have struggled with fatigue and markedly reduced brain function every afternoon. This is part of my family history: my father and grandfather both structured afternoon naps into their schedules. I have found that caffeine and nicotine are either ineffective or cause a jittery nerviness. The side effects of the antidepressants I tried — desipramine, Paxil and Wellbutrin — were not worth the minimal benefits.

At first, I used modafinil only when I desired an extended high level of attention. Previously, I could work competently on the fracture-mechanics of high-silica stone (while replicating ancient tool-flaking techniques) for about an hour. With modafinil, I could continue for almost three hours. It did not make me 'smarter', but extended the length of concentrated focus.

When I used it on a three-day cross-country drive, I was not only more alert but found the journey more enjoyable and less tiring than previously.

I have not seen any data suggesting that modafinil is either habit-forming or easily abused (I have not looked for studies in children). A 50-mg dose is quite low, but 100 mg does not increase the level or length of focus, for me at least, and can result in nervousness. As no 'high' is achieved, anyone taking too high a dose would soon cut down.

Competitive advantage is not a public-health issue at all, but a personal ethical and philosophical question. Today I will give my seven-year-old granddaughter a piano lesson, lead her in a chemistry experiment, listen to her sums and encourage her to enter any new words of her vocabulary into her personal dictionary. Am I trying to nurture her towards a 'competitive advantage'? You bet!