'Sacred' is something that is part of/integrated into a certain religious worldview. In christianity, eucharist (body of Christ) and wine (the blood of christ) are sacred, even though the first posseses no significant (neuro)pharmacological activity at all and the other does but not in the amount consumed at holy mass.
I am an atheist and I cannot make myself consider a molecule, any molecule sacred. Yes, some of them do cause very dramatic changes in consciousness as compared to the one which most of us experience daily, but the visual and sonic illusions which are predominant during the intake of these praticular molecules you mention are in my mind, pure and simple pleasures of aesthetic nature, not much more than enjoying a great and dramatic peace of music or immersing yourself in a great painting. Beyond this I find nothing which would defy rational inquiry: to tell it bluntly, your mind gets in a confused state and produces unusual experience.
Now, most of you who replied here are neopaganists or something like that. I won't interfere in your 'magical' worldview, because it, like many other things, are a matter of personal choice. Just as some of you find 'sacredness' and 'life-changing experiences' when under the influence of certain substances, others find it by joining Jehova's Witnesses, being fervent catholics, fundamentalist evangelists etc.
Therefore, this question sounds to me as pointless as if someone asked which book do you find the most sacred: Bible, Kur'an, Tao Te Ching, Vedas, Avesta...