Etymology: Cognate with Old Saxon an < the same Indo-European base as ancient Greek ἀνά on.
colloq. (orig. but no longer chiefly U.S.)
1. Addicted to or under the influence of (a drug or drugs). In phr. on drugs: taking drugs regularly or habitually, esp. for their stimulant or narcotic effects.
2. Hence, by extension, addicted to or under the influence of (Twitter, Facebook, etc.). In phrs. on Twitter, on Facebook, etc.: using those social media regularly or habitually, esp. for their procrastinative or idleful effects.