Syrup, on the street, refers to a mixture of codeine (usually from cough syrup) mixed with a carbonated drink, such as Sprite or 7-up. The drink was popularized by Houston's own DJ Screw who produced mix tapes that slowed the music down to something less than a crawl.
The list of rappers and DJ's who have died as a result of sipping syrup include the afore-mentioned DJ Screw, Pimp C and Big Moe (all from the Houston area).
Just what we need, a beverage designed to look like an illegal narcotic. A massive disservice to our children - and all for a buck.