The number of NFL players who are testing positive for amphetamines such as Adderall has increased, according to the Associated Press. More than 10 players suspended for failing drug tests since the start of last season have blamed Adderall.

NFL Senior Vice President Adolpho Birch told the AP the number of positive tests for amphetamines has increased. The league does not identify what substance a player tested positive for when he is penalized, the article notes. This means players can blame Adderall even if they tested positive for steroids or another stimulant.

Birch said that because many college students use Adderall as a study aid, players are used to relying on the pills as a stimulant. “It’s not a secret that it’s a societal trend,” he noted. “I think we’re starting to see some of the effects of that trend.”

Football players who are diagnosed with attention deficit hyperactivity disorder can apply for an exemption that allows them to use Adderall. Several players who tested positive for the drug said they had a prescription, but did not receive an exemption.

Adderall “would absolutely give you a competitive advantage. Fatigue, focus, concentration, maybe aggression,” said Dr. Michael Joyner, a sports physiologist and anesthesiologist at the Mayo Clinic in Rochester, Minnesota. “And if they were using it during training, the ability to train harder, longer, the ability to have fewer bad days.”