Green’s Dictionary of Slang

blow one’s mind v.

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

1. to become intoxicated with a drug or drugs.

[US]Billboard 9 Oct. 12: The company’s third label, Mirwood, is competing with two singles: ‘The Duck’ by Jackie Lee and ‘Blow Your Mind’ by the Gas Company.
[US]N.Y. Times 21 Mar. 1: He regularly turned on with marijuana or blew his mind with LSD.
[UK]Manchester Guardian Weekly 20 June 6: You can blow your mind every night of the year.
[US]D.E. Miller Bk of Jargon 339: blow your mind: To feel the effects of a strong dose of a mind-altering drug (especially an hallucinogen), implying that the reality of the user is transformed.
[UK]J. Baker Walking With Ghosts (2000) 83: You’ll take it away and give me a weight of Nepalese temple balls that’s guaranteed to blow my mind.
[UK]N. Griffiths Grits 86: Cut with crushed up dexies, Col says. — Blow yer fuckin mind, or what’s lefter the bastard.

2. to become mad, to lose one’s mind.

[US]H.S. Thompson letter 13 May in Proud Highway (1997) 611: I think he’s blown his mind; he’s now signing himself ‘Sydney’.

In phrases

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

(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.

[US]R.R. Lingeman Drugs from A to Z (1970) 47: blow-your-mind roulette A game played with barbiturate or stimulant pills. ‘A group of people turn out the lights and throw a large assortment of pills and capsules on the floor. They grope around and swallow the first pill they touch, then everyone waits to see if they got an uppie or downie, an innie or outie, or a carpet tack.’ Howard Smith, Village Voice (N.Y.) (1966).