College students who misuse prescription stimulant medications such as Adderall or Ritalin in an attempt to focus better while studying are at increased risk of misusing other substances including alcohol and marijuana, new research finds.

Stimulant medications are often prescribed for attention deficit hyperactivity disorder (ADHD). Some college students without a diagnosis of ADHD take these so-called study drugs because they think it will improve their academic ability, improve focus and increase their energy, according to the University of Georgia researchers.

They surveyed more than 600 college students about their substance use over the past month. About 20% of students said they had ever used a prescription stimulant, and 9% said they had used a stimulant in the past month. Those who reported any alcohol or marijuana use were three times more likely to use stimulants, HealthDay reports.

“Stimulant use may be a kind of catch-up behavior,” study author Ash Warnock said in a news release. “Some studies have shown that students who party with drugs and alcohol on the weekends use stimulants like an academic catch-up because they’re behind on their studies.”