The most famous example of the genre is, of course, Aldous Huxley's novel "Brave New World," published in 1932. In Huxley's vision of the 26th century, the drug Soma is used to ensure the obedience of the lower classes of a "perfect" eugenic world where people are bred specifically for the social function they perform.

More recently, in the Christian Bale film "Equilibrium" (2002), the citizens of a totalitarian city-state must take an emotion-killing drug as a means to prevent war. Those who refuse to take the drug, called Prozium, are labeled "sense offenders" and are violently hunted down and sentenced to death by a special caste of "clerics." Art, literature, and any expression of human emotion and creativity are prohibited.

Science-fiction writers return again and again to these scenarios because they raise fundamental questions about the nature of authority and social control. In doing so, they also ask us to question what it is that makes us truly human.

Would it be desirable to eliminate human imperfection with something as simple as a pill? Would the loss of certain "negative" or "destructive" aspects of our humanity be justified by the net gain to social order and the reduction in suffering? And would it be better to try to persuade ordinary people to surrender these aspects of themselves voluntarily for the greater good, or would an "enlightened" class of rulers have every reason to force people to do so, perhaps even without their knowledge?

The dramatization and the fictional settings shouldn't blind us to the fact that such possibilities are very real. Very real—and very close. Just how close has been revealed by new figures from Public Health Scotland, which show that more than a million men and women, close to a quarter of Scotland's adult population, are now being prescribed anti-depressants, powerful drugs with wide-ranging effects on mood and physical health. This probably makes Scotland the nation with the highest rate of anti-depressant use in the world. In the United States, by contrast, around 15 percent of adults are on anti-depressants, which is still, by any metric, a lot.