But Judge Suzana Pereira said Edson Cholbi do Nascimento, who must surrender his passport to the Sao Paulo court this week, can remain free as he appeals - which can take years in Brazil.
"The process is still open. He can still appeal and have another court review the case," Judge Pereira said.
She said she could not reveal many details about last week's ruling because both parties agreed to handle the case privately. But she said she found enough proof to convict Do Nascimento, 43.
Do Nascimento previously denied the charges, although he said he had used drugs out of curiosity after he quit professional football. He spent six months in a maximum-security prison in 2005 after being arrested with 50 others in a sweep aimed at a gang in the port city of Santos. Prosecutors said he was associated with the criminal group.
Pele is considered the best ever footballer and in Brazil he is hailed as a national hero. He is currently in the spotlight as the country makes final preparations to host the World Cup in 10 days.
His personal adviser, Jose Fornos Rodrigues, said the star was travelling in China and had no comment on the case.
Known as Edinho, Pele's son played as a goalkeeper and is now a coach for the Santos professional soccer team, where his father rose to fame in the 1950s. The club said it would not comment, calling the case a personal matter for Edinho.
It is not his first run-in with the law. He was charged in early 1990s with taking part in a high-speed race where the other car struck and killed a motorcyclist. He was sentenced for manslaughter years later, then acquitted in 2005.