He was suspended for 25 games without pay on July 23 after the positive test for the banned substance.
Maybin had said he used the substance to treat his attention deficit disorder, for which he previously had a therapeutic use exemption granted.
At the time of his suspension, Maybin was hitting .247, with one home run and nine RBIs in 62 games.
He was allowed to play in five minor league games before returning. He went 5-for-16 with two RBIs and two strikeouts for Triple-A El Paso.