Two sources told Tim Graham of The Buffalo News the team has been concerned about Dareus using marijuana since Chan Gailey's tenure as coach.
It's unknown if Dareus' arrest will trigger a suspension from the NFL. Though this is his first known offense since entering the league in 2011, a prior failed drug test or another situation could've led to him entering the league's intervention program.
Sgt. Steve Jarrett of the Alabama Department of Public Safety confirmed to AL.com that the substance found in Dareus' car following a traffic stop was synthetic marijuana, which can avoid detection in a drug test.
The arrest comes after Dareus was benched late last year for "habitual" tardiness.
The Bills picked up the fifth-year option on Dareus' rookie contract last month, keeping him under team control through the 2015 season. The team has become a safe haven for players with checkered histories -- Brandon Spikes and Mike Williams were both acquired in the offseason.
Dareus is coming off his best season, earning Pro Bowl honors for the first time in his career. His production gives him more rope in the organization, but you wonder how thin the team's patience is getting.