The sprinter was tested positive for Methylprednisolone during the Canadian Track League meet on July 6 in Edmonton.
Spearmon said the the drug was in a prescription he was taking and that he didn't know that it was on USADA's and the World Anti-Doping Agency's banned list.
Spearmon could have asked for a therapeutic exemption to continue taking the drug but failed to do so.
"After a thorough review of the case, including Spearmon's medical records, USADA has accepted Spearmon's explanation that the Methylprednisolone was not being used in an effort to enhance his performance," USADA said.
His suspension began August 27 meaning he will be eligible to compete again in just nine weeks.