More NFL players are testing positive for amphetamines, a class of substances that includes the ADHD drug Adderall.

Since the start of last season, more than 10 players suspended for failing drug tests have publicly blamed it on taking the stimulant. And while the league doesn’t identify the substance when a player is penalized, senior vice president Adolpho Birch acknowledges that the number of positives for amphetamines has increased.