Turns out, this is a carbonated, grape-flavored beverage spiked with melatonin, valerian root and rose hips. Apparently it is "very, very popular in Houston," and it's sold throughout the south in liquor and convenience stores.
So, does it make you sleepy? I asked the publicist. Yes, and she hears it's good with vodka. Oh, something that makes it more likely I'll fall asleep while drinking? Excellent.