Rapper T.I. may have been sippin' on sizzurp after all the night of his felony drug possession arrest -- because cops say dude had the main ingredient, codeine, when he was busted.
T.I.'s probation officer just filed documents in Georgia that say L.A. County Sheriff's deputies found codeine, marijuana and ecstasy in T.I.'s possession during the September 1 arrest.

As we first reported, T.I. had several Styrofoam cups in his Maybach that night (pictured above). Sizzurp -- aka codeine syrup -- is commonly served in Styrofoam cups.

The document also states that T.I. tested positive for opiates the day after the arrest, but does not name a specific drug. Neither marijuana nor ecstasy are opiates.

UPDATE: Sources connected to the case tell us that despite the presence of codeine -- there was no codeine syrup ... the essential ingredient in sizzurp.