Harrison held a conference call with Boston area media to make a statement, saying NFL Commissioner Roger Goodell would make the suspension official Saturday.
"I'm basically here to let you all know that tomorrow the commissioner will announce that I've been suspended by the NFL for violating the league policy on banned substances," Harrison said. "That suspension will be four games.
"I want to make it clear that not once did I ever use steroids. I did admit to the commissioner that I did in fact use a banned substance. My purpose was never to gain a competitive edge. Rather, my use was solely for accelerating the healing process of injuries I sustained while playing football."
This will be Harrison's 14th season in the league and his fifth with New England. He has 32 career interceptions.