Green’s Dictionary of Slang

1. something that is astonishing, remarkable.

1967–8		Baker et al. CUSS.
1968		T. Wolfe Electric Kool-Aid Acid Test (1969) 13: The thing was fantastic, a freaking mind-blower.
1969		Gandalf’s Garden 6 n.d. 11: mindblower an experience or idea which changes one’s thought pattern, enlivening the mind and emotions.
1969		Harvard Crimson 17 Nov. 🌐 Night, the final play of the trilogy, is in every way the third act of the evening. It is an answer to the chaotic world depicted in the first two plays [...] It is both devastating and exhilirating, an even bigger mind-blow than Morning or Noon.
1977		C. McFadden Serial 43: It was just a mind-blower that they’d all survived.

2. a psychedelic drug.

1968		New Scientist 27 June 703: One might be a real mind-blower and the other as ineffective as a sugar lump.
1979		H. Feldman et al. Angel Dust 128: One user heard on television it was a mind-blower and so went out to buy it.

3. a hallucinogenic drug-user.

1969

Time 30 May 55: For most of the 19th century’s mind blowers, opium meant laudanum.