A trank was a term used in 2015 for a person under the influence of chemicals. The process of using them was to be tranked.
They usually were taken via tranquilization, thus the name for those using it. A test for tranquilization was to smell the user's ears.
When Officers Foley and Reese of Hill Valley Police Department's Unit N11-11 picked up Jennifer Parker, they believed she was tranked. One of the cops instructed the other to sniff her ears to make certain.