Srila Prabhupada address the use of psychedelic drugs as a means to attain mystical experiences in the following quote:
Hayagriva: Today, people claim to induce mystical states through psychedelic drugs.
Prabhupada: These are artificial means, and they cannot be sustained. It is better to engage in the bona fide devotional process -- sravanam kirtanam visnohsmaranam pada-sevanam [SB. 7.5.23] -- always hearing about Krsna, talking about Him, remembering Him, serving Him in the temple, distributing His literatures, and so on. There are many services we can render in order to be fully absorbed in Krsna consciousness.