Play video content TMZ.com

Rapper Lil Xan made the crowd at his L.A. show see double, and prescription drugs had noting to do with it ... it was all about his celebrity look-alike, Ethan Cutkosky.

Seriously, the "Shameless" star is a dead ringer for the Cali rapper ... and on Wednesday night they shared the stage. If not for the face tattoos, the crowd would've really been confused.

Xan surprised his fans by bringing Ethan out while he performed his new cut, "The Man" ... which is off his upcoming album, "Total Xanarchy."

We got the rapper recently in N.Y., and he told us he and the actor are real life homies. Xan said he has plans to work with Ethan in the near future, and based on how the crowd reacted to their onstage debut together ... these guys should make it happen soon.

Just sayin' ...