After breaking his leg and piling on 50lbs, John Smith took Vyvanse to suppress his ap?petite. This was on the advice of a medical-student friend who had lost a “near-miraculous” 20lbs despite no change to his lifestyle. Vyvanse did the trick: Mr Smith swiftly shed the excess weight.

However, he also noticed that when he used Vyvanse, a prescription drug to treat binge-eating and attention deficit hyperactivity disorder (ADHD) in children and adults, he could “hyper-focus” on his work. Now the 30-year-old (who chose a pseudonym when interviewed for this article) “pops a small dose” every time he needs to power through his work as an analyst for an investment group in the US.

Vyvanse lets him shut off the world, put his head down and dive into numbers. “I feel a desire to track down the answers. It creates an obsessive compulsive desire for me to check off my work as completed — and completed well.”