Sources close to "How High 2" tell TMZ ... the hip-hop duo wasn't cast in the made-for-TV movie after starring in the original stoner comedy.
We're told the sequel is going to be fundamentally different from the OG version -- think sativa vs. indica -- because it's for a television PG-13 audience, and weed legalization has made strides since 2001, when Meth and Red blazed their way through Harvard.
Meth and Red are MIA -- probably ripping a bong somewhere -- but one of the original producers, Shauna Garr, is returning.
Don't write off Meth and Red just yet ... we're told there's always a chance the duo changes course and makes a cameo in the sequel, or in a potential trilogy.
One more puff wouldn't hurt, right?