Green’s Dictionary of Slang

drop v.6

[one drops them down one’s throat]

1. [1960s+] (drugs) to consume pills or any drug that can be taken orally.

2. [1980s] to drink (beer).

In phrases

drop a roll (v.) (also drop a rack) [rack n.2 (5)/roll n. (4a)]

[1980s] (US drugs) to take three to five pills, of various types of drug.