The 17-year-old failed an in-competition drugs test after Sunderland's Under-18s match against Aston Villa on September 22 last year.
He tested positive for recreational drugs cocaine and cannabis and he was handed a mandatory two-year ban for breaching the Football Association's anti-doping regulations in December.
His scholarship at Sunderland was terminated immediately, but he appealed the decision - but that was recently withdrawn and the FA punishment has now been finalised.
Sunderland chief executive Margaret Byrne said in a statement: "Empowering and educating our young people to make the right choices and decisions both on and off the field is fundamental to our academy philosophy and ethos.
"We expect the highest standards of all players who have the honour of being part of Sunderland AFC, which is why this came as such as shock to us.
"It was enormously disappointing for everyone at the club who works so hard to support our young players and give them every opportunity to make it as professional footballers.
"We are strong advocates of the rigorous testing programme that our sport adheres to and we will continue to educate and advise all of our young players as to the enormous dangers of drug use."
Sunderland academy manager Ged McNamee added: "Lewis not only let our club down, he let himself down and his team-mates down massively. We took the strongest possible action in terminating his contract as every footballer knows the severe consequences of this type of offence.
"We have, however, worked to ensure that support and assistance was available to the player and his family through what has undoubtedly been a difficult and challenging time for them."