Last year, I had my own brief experiment with smart drugs. I felt burned out after a series of long foreign assignments, and my brain was rustily chug-chugging along at half-speed. That's when I first read about a drug being billed as "Viagra for the brain" – not Ritalin, but Provigil, a brand name for modafinil.

It was originally designed for narcoleptics, but clinical trials stumbled across something odd: if you give it to non-narcoleptics, they become smarter. Their memory and concentration improves considerably, and so does their IQ. There were no known side-effects, except – oh, thank you! – weight loss.

I hunted it down online. A week later, the little white pills arrived in the post. Within a few hours of a 200mg dose, I found myself gliding into a state of long, deep concentration, able to read a book for six or seven hours at a time without looking up. My mood wasn't any different; I wasn't high. It was like I had opened a window in my brain and all the stuffy air had seeped out, to be replaced by a calm breeze. On Provigil, I had the most productive month of my life, writing reams of articles. I didn't notice any side-effects – until the third week.

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At any given time, only a small amount of your brainpower is dedicated to the tasks immediately in front of you. The rest is working on other stuff – processing memories, your subconscious, your creative thoughts. But Provigil points all your mental guns forward. It deploys far more of your brainpower on to your direct task.

It's great at first – but it has a cost. After a while, you realise that your mental life is oddly depleted. Creative thoughts don't come to you any more. You are running on the imaginative store you built up before Provigil, and whizzing through it efficiently, but you aren't inventing anything new. That part of your brain is undernourished. You feel fast and flat.

When I stopped taking them, my brain went back to its slower, scrappier state – but my creative impulses came back. I was more spontaneous again. So I have cut a deal with myself. I keep a pack in the bathroom cabinet for the days when I am really knackered and have to be able to work fast and fluently – but I don't ever take more than one or two a month.

But if I ever had to do exams again, I would take Provigil. And here's the ethical dilemma. Is this the equivalent of athletes taking steroids? Does it create an unfair pressure for other people to take these drugs – which are still pretty expensive – to keep up with other students and co-workers? Or would we be unfairly holding the human race back by refusing to smarten up?

We can't escape these dilemmas now. Smart drugs are only going to become more subtle and powerful as money flows in. As Professor Anjan Chatterjee says: "This age of cosmetic neurology is coming, and we need to know it's coming." My little pack of Provigil is a challenge to us all.