Vic Mensa's having a bad trip -- back from Africa, that is -- because U.S. Customs Agents have him in custody for allegedly returning with a stash of mushrooms ... TMZ has learned.
The rapper was taken into custody Saturday at Dulles International Airport outside D.C. ... where he'd just returned from Ghana. According to our law enforcement sources, Vic was pulled aside for a secondary search, and that's when agents found what they believe are shrooms.
We're told the feds are still testing the substance they allegedly found to confirm it is what they think it is.
Vic was booked for felony narcotics possession. Fun fact: Psilocybin (the scientific name for shrooms) remains a Schedule I substance under federal law -- although there's now a push in some states to legalize it ... and they've already been decriminalized in some communities.