Green’s Dictionary of Slang

blow one’s mind v.

also blow one’s head off
[SE blow, explode + mind]
[1960s+] (orig. drugs)

1. to become intoxicated with a drug or drugs.

2. to become mad, to lose one’s mind.

In phrases

blow your mind roulette (n.) [SE Russian roulette]

[1960s] (US black/drugs) a drug-based game whereby the participants toss a variety of unspecified pills onto a table and then take whatever they fancy and wait to discover what the effects will be.