Forty participants were recruited to participate in two placebo-controlled, double-blind, crossover studies examining the LSD-induced alterations of consciousness and mystical-type experiences. Twenty-four and sixteen participants were administered 100 and 200 μg of LSD, respectively. Participants were involved in two experimental test sessions (LSD and placebo) in a balanced order with a washout period of at least 7 days between sessions. Alterations of consciousness were assessed using the 5D-ASC scale and LSD blood plasma concentrations were analyzed using validated liquid-chromatography-tandem mass-spectrometry. After 200 μg of LSD, Mystical experiences were also assessed using the 43-item MEQ embedded in the 100-item States of Consciousness Questionnaire (SOCQ). LSD-induced alterations of consciousness were significantly correlated with ratings of mystical experience while plasma LSD concentrations were not positively correlated with ratings of peak subjective effects on the 5D-ASC scale or MEQ.