In the meantime, with no end to the Amphetamine Age in sight, smarter answers are needed for the unanswered questions about the drugs people already take in the hope of enhancing their cognitive powers – questions about whether they work, how they work, whether they work differently in people with different gene variants, the effects they have on the mind after their initial novelty has worn off, and the effects they may have on our health and wellbeing in the long term.

Despite decades of study, a full picture has yet to emerge of the cognitive effects of the classic psychostimulants and modafinil. Recent reviews indicate that they may help to lay down long-term memories and perhaps help keep information present to hand in working memory. They may also enhance ‘cognitive control’, the ability to adapt behaviour in changing conditions, particularly in people whose powers of cognitive control are modest to start with.

Part of the problem is that getting rats, or indeed students, to do puzzles in laboratories may not be a reliable guide to drugs’ effects in the wider world. Drugs have complicated effects on individuals living complicated lives. Determining that methylphenidate enhances cognition in rats by acting on their prefrontal cortex doesn’t tell you the potential impact that its effects on mood or motivation may have on human cognition.

It may also be necessary to ask not just whether a drug enhances cognition, but in whom. Researchers at the University of Sussex have found that nicotine improved performance on memory tests in young adults who carried one variant of a particular gene but not in those with a different version. In addition, there are already hints that the smarter you are, the less smart drugs will do for you. One study found that modafinil improved performance in a group of students whose mean IQ was 106, but not in a group with an average of 115.

There are smarter questions to ask about fairness and cognition-affecting drugs. So far, the ethical anxieties have revolved around elite competition: whether students who take drugs to enhance performance are cheating, and whether they will put pressure on their peers to do likewise to avoid being at a competitive disadvantage. But attention is not just a problem for the minority who reach higher education or certain professions.

In their book Scarcity: Why having too little means so much, Sendhil Mullainathan and Eldar Shafir describe how they dumbed people down by inducing them to think about the cost of living. Recruiting shoppers from a New Jersey mall, they prefaced cognition tests with a hypothetical question that invited respondents to imagine they had to get their cars serviced. They also asked the shoppers to disclose their household incomes. When the price of the service was given as $300, the scores of rich and poor were indistinguishable. When it was $3,000, the poorer shoppers scored worse; in fact, their scores were worse than those of people who did similar tests after a night without sleep. Their results implied a drop in IQ of 13 or 14 points, the difference between average and ‘borderline deficient’ intelligence.

Mullainathan and Shafir argue that the increase in the imaginary cost triggered a reallocation of mental capacity among those for whom such a sum would be a serious problem in real life. It activated thought processes that would not shut off, reducing the computational power available to process the intelligence tests. If that is what a hypothetical problem can do, the effects of poverty and money worries in the real world must be a cognitive scandal of staggering proportions.

Mullainathan and Shafir’s work points towards a bigger picture of fairness in cognitive enhancement. One message that has emerged from the research so far is that cognition-affecting drugs do more for lower performers than high-fliers and that they can offset disadvantages, such as lack of sleep. Drugs that promote concentration might help poor people in their efforts to better themselves – studying at night school while fatigued from long hours of labour, for example – or, if Sarter is right about how improving focused attention can make it easier to deal with multiple demands, in coping with bills that outnumber earnings.

It’s certainly better to enhance cognitive performance through healthy living, fitness and educational opportunities than by taking pills. But we also have to recognise that it is far harder for the poor to achieve best cognitive practice than the rich. The question of whether drugs could help people get out of poverty, by offsetting its cognitive impact on them, might actually be the smartest question we can ask about smart drugs.