Green’s Dictionary of Slang

drops n.²

(UK Und.) alcoholic drinks, usu. gin.

1818		W. Perry London Guide.
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc.

In phrases

fond of one’s drops (adj.)

used of a heavy drinker.

1902

H. Baumann Londinismen (2nd edn).

take one’s drops (v.)

to drink heavily.

1737

B. Franklin ‘Drinkers Dictionary’ in Pennsylvania Gazette 6 Jan. in AS XII:2 90: They come to be well understood to signify plainly that A MAN IS DRUNK. [...] Took his Drops.