Sahakian and Morein-Zamir revive questions about the widespread availability and diversion of prescription medications for non-clinical use in healthy individuals (Nature 450, 1157–1159; 2007). Such questions drove legislators to impose controls a few decades ago, when amphetamines and barbiturates were widely available.

Because the diversion of drugs is linked to their availability, the World Health Organization monitors their production and consumption by individual nations. In the United States, production of stimulant drugs has soared during the past two decades, and enough are now produced each year for the daily treatment of at least four million individuals. Even though stimulants and other cognitive enhancers are intended for legitimate clinical use, history predicts that greater availability will lead to an increase in diversion, misuse and abuse. Among high-school students, abuse of prescription medications is second only to cannabis use.

Although access to medications that improve our cognitive performance might be desirable in theory, these may have adverse medical consequences. Some limitations are necesssary, for these medications can be addictive. This is because cognitive enhancers such as the stimulants methylphenidate (Ritalin) and amphetamine amplify the activity of dopamine, a neurotransmitter that increases saliency, making cognitive tasks and everyday activities seem more interesting and rewarding. This learned experience can lead to abuse of the drug and to compulsive use and addiction in vulnerable people.

As we increase our knowledge of how the brain works, we may one day have safe interventions to improve cognition. In the meantime, we need to learn from history and avoid using them unnecessarily.