Green’s Dictionary of Slang

1. drugged alcohol.

1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 97: Hocus, or hocus-pocus [...] A deleterious drug mixed with wine, etc. which enfeebles the person acted upon. Horses too are hocussed, at times.
1937–84		Partridge DSUE (1984) 558: —1823; † by 1893, hocus being then general.

2. marijuana.

2001

Pop Boffin issue 5 🌐 Hocus pocus as in ‘Some bitch-ass muthafucka sold my ass some hocus pocus-ass shit’ rap slang for marijuana.