Lil Scrappy -- I've Been Weed Free For 30 Days!

Lil Scrappy can finally pee in a cup sans stress ... because the rapper has purged himself of the green stuff for 30 days ...TMZ has learned.

We broke the story ... The "Love & Hip Hop: ATL" star voluntarily checked himself into rehab on May 30th -- after failing a court-ordered drug test. He copped to the fact he was addicted to ganja and wanted help.

Lil Scrappy's lawyer Mawuli Mel Davis tells TMZ ... Scrappy was able to kick his nasty habit and the rapper was released at 12:01 AM Saturday, practically a new man. He explains, "Scrappy has had time to reflect, read, and write. He is now drug and alcohol free."

To pass on his newfound wisdom, we're told Scrappy will start mentoring teens next week -- speaking to them about what he's gone through and how to keep their noses clean. Maybe a little too soon, but ...