From purple + drank.
purple drank (uncountable)
- (slang) A recreational drug based on cough syrup, popular in the hip-hop community in the southern United States.
2007, Kenny Attaway, Slum Beautiful, page 40:The infamous purple drank made me dizzy and sick, but I loved its aftertaste.
2011, Kenaz Filan, The Power of the Poppy: Harnessing Nature's Most Dangerous Plant Ally, page 211:Instead of listening to the message, people find it easier to blame the messenger. Hip-hop may have promoted purple drank, but it did not create it. OxyContin abuse became a national emergency without a backing soundtrack.