Millennials took Adderall to get through school. Now they’ve taken their addiction to the workplace.

In 2010, when Raphael was a first-semester college freshman struggling to get through finals, he did what it seemed like all his friends were doing: he got an Adderall from a fellow student and holed up in the library. It was the first time he’d tried the stimulant—a mixture of amphetamine salts often prescribed for attention deficit hyperactivity disorder (ADHD)—which is often used off-label as a “study drug” by those not diagnosed with the disorder.

“I was a little surprised by how much I loved it,” Raphael, now 25, tells Quartz. “It made me feel like a philosopher-king.” Soon, he became part of the estimated 20% of college students who abuse prescription stimulants. But he didn’t anticipate that, six years later, he’d be using Adderall daily while working as a web developer at an e-commerce shop in Los Angeles.

The National Institute on Drug Abuse is looking into this relatively new trend, however: A recent study of 11 million US workers found that workplace drug tests are coming back positive at the highest rates in a decade, and they’re continuing to increase. Amphetamines, including Ritalin and Adderall, were the second most common drugs detected after marijuana.

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