"The Korova milkbar sold milk-plus, milk plus vellocet or synthemesc or drencrom, which is what we were drinking."
Moloko Plus or Knifey Moloko, stemmed from the Russian word for milk, is the barbiturate-spiked milk served within the Korova Milk Bar. It's mentioned in both the movie and book when Alex and his droogs drink drencrom to prepare for a night of violence and just in the book when Alex returns alone after his release from State Jail 84f.
There are three types of Moloko plus served within the Milk Bar; vellocet (mixed with most likely amphetamines), synthemesc (mixed with synthetic mescaline) and drencrom (mixed with adrenochrome and possibly unnamed hallucinogens). It can be served to minors because of its lack of alcohol.