Stimulants like methylphenidate (Ritalin) and mixed amphetamine salts (Adderall) have clear benefits for those with attention deficit/hyperactivity disorder (ADHD). But what about for those without ADHD: Do these drugs improve cognitive ability in otherwise healthy brains?

It's easy to imagine the potential advantages if they do—better grades, greater productivity, more creativity. But there may be costs as well, since stimulants have well-known side effects like sleep problems and appetite suppression, not to mention potential dependence and withdrawal.

To explore these questions, I turned to Martha Farah, a pioneer in the growing field of neuroethics and director of the Center for Neuroscience and Society at the University of Pennsylvania. (Full disclosure: Farah was my PhD advisor and is a friend.)

When she and her colleagues set out to explore the effects of stimulants on college students' performance, they wondered not if the drugs would enhance cognitive ability but rather how big the effect would be, and whether certain mental abilities would be affected more than others. What they found was something quite different.

The research team had participants complete a battery of 13 cognitive tests after taking either mixed amphetamine salts or a placebo; all participants completed both conditions, and neither they nor the researchers knew which pill they got (in other words, it was a double-blind study).

Much to their surprise, the research team found no differences between the two conditions—with one exception, as Farah explained: "The one question on which placebo and mixed amphetamine salts differed was, 'Do you think that your performance on these cognitive tests today was enhanced by the pill you took?' And the days they were on the amphetamine, they rated the enhancement more strongly than the days they were on the placebo."

These findings are supported by research from other groups, including an article by Scott Vrecko entitled, "Just how cognitive is 'cognitive enhancement'?" He concluded that the benefits of stimulants on academic performance likely come from their effects on students' energy, interest, drive, and enjoyment of the work, rather than on their actual cognitive ability.

Farah described similar effects of these drugs on energy and optimism: "Students felt a certain gusto on this drug for approaching tasks that felt daunting." Rather than making them smarter, they experienced a change in their "feelings and attitudes toward the work."

And as anyone who's struggled to complete a difficult but necessary task knows, that kind of boost is enormously helpful. "Feeling optimistic, feeling capable, feeling energized—that's a big help," Farah explained, "even if your actual cognition is not being enhanced. They don't make you smarter but they certainly can make you better able to deploy whatever smarts you have to do cognitive work."

Greater optimism, higher motivation, better performance...these all sound like good things. They likely account for the high numbers of students on college campuses who use these medications without a prescription—as "study drugs," as Farah said. So what's the downside?

As mentioned above, there are common side effects, like sleep disruption. And because they make a person feel good, they have a high risk for abuse and addiction. Farah also mentioned the possibility of having psychotic experiences, which is less common but has long been recognized as a risk of stimulant use.

The bottom line? According to Farah, prescription stimulants can prevent people from falling asleep and "give them a sense of can-do energy," but "don't actually improve test scores or learning ability or anything like that."

Needless to say, never take prescription medications that aren't prescribed to you by a doctor.

—Seth J. Gillihan, PhD