The first definition already listed is accurate as to the meaning and general composition:
-Promethazine
-Codeine syrup
-Any clear soda (often fruit flavored)
-One or more Jolly Ranchers for flavor
There are many variations and differing usage, but in order to be considered true and unadulterated sizzurp, the above ingredients are necessary.
The likely etymology is from the word "syrup", pronounced with a Southern accent like "
surrup", or just "
surp" when spoken loosely.
Ebonified with "
-izz" (like hizzouse to mean house), forms "sizzurp".