I found an interesting article which suggests that some psychedelics, such as mescaline cacti and mushrooms, promote unitive or non-dual spiritual experiences which are characterized by the feeling or understanding that "all is one" in the universe and that you yourself are connected to and one with everything else.
On the other hand, other psychedelics, such as ayahuasca/DMT, promote a different type of spiritual experience. This is typically more of a non-unitive experience which is characterized by the feeling that you are envisioning or communicating with other life forms or entities separate from yourself.
The article relates these different types of spiritual experiences with different mystical traditions. The writings of Aldous Huxley were based on his experiences with mescaline, which nicely complemented the unitive mysticism of the Vendanta tradition which he followed.
The Doors of Perception was a very important publication which helped launch the whole psychedelic movement. Naturally, generations of psychedelic users have been strongly influenced by Huxley's views, and his unitive "all is one" outlook has historically been seen as the highest form of spiritual and psychedelic experience.
In recent years however, ayahuasca and DMT have begun to grow in popularity. (Note that I have posted two recent articles that discuss the growth in popularity of ayahuasca: see
here and
here). The article's thesis is that the increasing use of ayahuasca will lead to a resurgence in mystical traditions which espouse a non-unitive outlook, such as the Jewish mysticism of Kabbalah.
Anyway, all of the above is just a summary of the article - it's not necessarily my view. But I do find it to be very interesting and plausible. Based on what SWIM tells me of his experiences with mescaline cacti and mushrooms, he would definitely agree that these psychedelics promote the unitive, "all is one" experience. SWIM has not yet tried ayahuasca, but the idea that it promotes more of a non-unitive experience is certainly consistent with all the ayahuasca/DMT reports he's read where people feel that they are communicating with other life forms or entities.
I will post the article below. It's an interesting read.