The suspension came in December after authorities cited Thornton for misdemeanor simple possession of marijuana and drug paraphernalia. Police had visited an apartment he shared with teammates in a sexual battery investigation, with a probable cause affidavit for a search warrant listing Thornton as the suspect.
Lee Turner, Thornton's attorney, says authorities dismissed charges because Thornton was not present during the search and passed drug tests. Thornton was not charged in the sexual battery case.
Doeren said Wednesday that Thornton, last year's leading rusher with 768 yards, has "met every expectation on and off the field" to return to "full status."
Thornton has practiced with the team in spring and preseason drills.
Thornton received counseling as part of a deal with the court to defer prosecution for a June 2013 charge of misdemeanor assault on a female. Turner said Thornton has complied with court requirements, which could lead to the dismissal of the charge Aug. 20.
Doeren suspended Thornton for last year's opener due to that arrest, although Thornton gradually earned back a leading role and twice ran for 100 yards -- including 173 yards and two touchdowns against Florida State.