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.

via Johann Hari.