What are cognitive-enhancing drugs, who uses them and do they work? Newsnight's Susan Watts has been finding out.
Most of us want to reach our true potential. We might drink a cup of coffee to stay awake and alert, or go for a run, to feel on top of the job. So where's the harm in a pill - a "smart drug" - that can do the same thing?
These so-called cognitive-enhancing drugs are usually prescribed to treat medical conditions, but known for their power to improve memory or focus.
Many people buy them over the internet, which is risky because they don't know what they're getting.
And we also know next to nothing about the long-term effects on the brains of healthy people, particularly the young.
But some scientists believe they could have a beneficial role to play in society, if properly regulated.
So who's taking what? Over the past week, Newsnight and New Scientist magazine have been running an anonymous online questionnaire of readers.
And I also decided to try one cognitive enhancer, modafinil, to see if it had any effect on me.
We were surprised by the volume of replies, 761, of whom 38% said they had taken cognitive-enhancing drugs.
Of those, nearly 40% said they had bought the drug online, and 92%t said they would try it again.
The survey is not representative of society as a whole, but it is an interesting, anecdotal snapshot of a world for which there is little hard data. The range of experiences is striking, and reminiscent of the science-fiction movie, Limitless.
"I was able to write a 22-page paper in one day. I revised it over the next couple of days and got an A. Normally, I wouldn't have even been able to get a rough draft done in a week."
"Did not help me do anything but feel anxious and excited, could not sit still even 15 hours later."
People said they had taken drugs that included modafinil (brand name Provigil, normally prescribed for sleep disorders), Ritalin (given to people with ADHD) and Adderall (a mixture of amphetamine salts, not licensed in the UK).
When asked about their potential impact on society, people clearly have concerns beyond safety - about how the drugs might create a two-tier education system in which some can afford the drugs and others can't. They voice wider concerns too.
"I want one as a student, but I don't want criminals on cognitive enhancers running around."
"The drugs would get stronger and stronger due to increased demand of performance. Addictions would ensue. People would not be able to live without them. Employers would demand their employees to be constantly using them."
We talked to one student about his experience with modafinil. Laurie Pycroft, at age 16, formed the Pro-Test group in Oxford, to argue the case for using animals in scientific research.
That was six years ago. He is now in his second year at Oxford University, studying physiological sciences - with an interest in neuropharmocology.
"I've taken modafinil a few times, primarily for its ability to increase wakefulness and allow me to concentrate and stay awake for very extended periods of time. I don't take it very often but if I want to stay awake for 20 or 30 hours, working on an essay it's very useful," he told the BBC's Newsnight programme.
Keen to learn more, I contacted Prof Barbara Sahakian, at the unit of brain and mind sciences at Cambridge University.
She and her team work with patients suffering from conditions such as Alzheimer's disease and Parkinson's, in which cognition can be significantly impaired.
They are researching the use of cognitive-enhancing drugs, such as modafinil, to see if they help such patients.
But Prof Sahakian thinks these drugs could play a far wider role in society. Her most recent research showed that sleep-deprived surgeons performed better on modafinil.
"I do think we've undervalued them. The Academy of Medical Sciences report in 2008 showed that even a small 10% improvement in a memory score could lead to a higher A-level grade or degree class, and that is a big improvement.
"As a society, we could perhaps move forward if we all had a form of cognitive enhancement that was safe."
In my self-experimentation with modafinil, I had to satisfy the neurologist, Dr James Rowe, that there were no risks for me, plus we had trained medical staff nearby in case of any unforeseen difficulties.
I took one tablet on two separate days, without knowing which one was the placebo.
After waiting a couple of hours to allow the drug to take effect, I carried out an hour or so of computer-based tests. These are largely "games", involving memory, strategy, planning and tests of impulsiveness.
So how did it feel? Well, on both days, I was waiting for some big effect that didn't come. I really could not tell on which day I had been given the real thing.
In fact, when asked to guess, I chose the wrong one. Interestingly, I recall telling colleagues that on the second day I felt "more myself".
In fact, that was the day I had been given the modafinil. And that description echoes some of those reported in our survey.
On the first day, I was tired. On the second, I had just returned from holiday. And then there is the so-called "practice effect" - the second time round I knew what to expect. So, by all accounts, you would expect me to perform better second time - which I did.
On impulsivity, I was more controlled. And on one memory recognition task, where I had to recall patterns at the end of the test that I had seen at the beginning, my score went up from 8/10 to 9/10 - a 10% absolute increase in the score.
Here's how neurologist James Rowe summed up the findings. "What we've seen today, taking modafinil, is some very striking improvements… in memory and, for example, your planning abilities and on impulsivity."
Long term studies
I still find it surprising that students turning to cognitive enhancing drugs are prepared to take the risk of buying them without knowing what they contain for these sorts of margins in performance.
It is human nature to want to push against our limitations, but what about the risks?
Regulators would require long-term safety studies on healthy people so they could weigh up risks and benefits before considering extending their licences.
Pharmaceutical companies are not exactly rushing to carry out such studies, but Prof Sahakian is calling for such work to be done, before someone comes to harm.
Some cognitive enhancers, such as Ritalin, are classed as controlled drugs. Modafinil is not, so it is not illegal to buy it online, though it is illegal to supply it, without a prescription.
The government, through the MHRA (the Medicines and Healthcare products Regulatory Agency), told us that tackling the illegal sale and supply of medicines over the internet is a priority.
But the attraction of a pill that makes us smarter will not go away. And though it might mean a difference of just a few per cent now, what if that were a 50% or 100%. Would we still say no?
Try your hand at one of the tests
Test produced by Cambridge Cognition.