Richardson said during an interview on SiriusXM NFL Radio that his two-game suspension to start last season was marijuana-related.
"A lot of (NFL) coaches and scouts, they already know about it," Richardson said, according to The Sporting News' Alex Marvez, the co-host of the interview.
Richardson's other off-field problems include an arrest for DUI in the early morning hours of Nov. 1, 2015 and a subsequent one-game suspension.
NFLDraftScout.com lists Richardson (6-5, 322) as the 12th-best offensive tackle in the 2018 NFL Draft, projected as a fourth-round pick.
"Richardson starred at tackle for the Wolfpack, but his powerful frame suggests a move inside to guard may be in his future," wrote NFLDraftScout.com senior analyst Rob Rang. "Fortunately, Richardson possesses the initial quickness and raw power to handle this conversion if -- perhaps a big if -- he fully commits to his craft."
Richardson, a second-team All-ACC selection, did not allow a sack or a quarterback pressure in his 11 games played in 2017.
"I wasn't mad at anyone else but myself," Richardson said during the SiriusXM NFL Radio interview. "I took my anger out in the weight room, on the field training and on all the things that would do nothing but make me ready for the season."
Richardson is scheduled to participate in the NFL Combine later this month in Indianapolis.