According to a study published in Human Psychopharmacology in 2000, LSD and psilocybin interfere with the subjective effects of alcohol consumption. In a majority of cases, those who had ingested LSD along with alcohol reported the effects of alcohol could not be felt. Those who had ingested psilocybin along with alcohol reported a reduction in the effects of alcohol, but not a complete blockage.
Twenty-two individuals that had used LSD and/or psilocybin with alcohol were interviewed about their experiences with these drugs. Of the 22 participants, 19 were male and 3 were female, and all were 18 to 28 years old.
According to the authors of this study, about 87% of those that had used LSD in combination with alcohol reported that the effects of alcohol were completely blocked. The remaining participants reported that, although the effects of alcohol were not completely blocked, there was a significant reduction in its effects. Of those who reported using psilocybin in conjunction with alcohol, 60% reported a reduced effect of alcohol, 34% reported no discernible change in effects, and 6.7% reported the effects of alcohol were increased.
None of the participants reported the effects of either psilocybin or LSD to be reduced by alcohol.
Barrett, S.P., Archambault, J., Engelberg, M.J. & Pihl, R.O. (2000). Hallucinogenic drugs attenuate the subjective response to alcohol in humans. Human Psychopharmacology, Vol 15: 559-565.