Fading fast at 11 p.m., Elizabeth texted her dealer and waited just 30 minutes for him to reach her third-floor New York apartment. She handed him a wad of twenties and fifties, received a tattered envelope of pills, and returned to her computer.

Her PowerPoint needed another four hours. Investors in her health-technology start-up wanted re-crunched numbers, a presentation begged for bullet points and emails from global developers would keep arriving well past midnight.

She gulped down one pill — pale orange, like baby aspirin — and then, reconsidering, took one of the pinks, too.

“O.K., now I can work,” Elizabeth exhaled. Several minutes later, she felt her brain snap to attention. She pushed her glasses up her nose and churned until 7 a.m. Only then did she sleep for 90 minutes, before arriving at her office at 9.