(By the way, psilocybin, from magic mushrooms, is extremely similar to DMT.) The two commonest methods of administration are smoking and ingesting. The smoking method is sometimes called "the businessman's trip," because it comes on almost immediately and only lasts for 20 minutes or so (compared to LSD's 8-10 hours). The ingesting pathway is a bit more interesting. DMT makes one half of the famous ayahuasca traditional mixture prepared by Amazon shamans. DMT is not normally active orally (it will be metabolized), so one must take a monoamine oxidase inhibitor (MAOI—like harmaline) in combination. The ayahuasca preparation is usually just a blend of herbs containing DMT and an MAOI.
Pharmacologically, DMT does a lot of very complicated things, but I think a simple picture will give you a flavor:
This is serotonin, one of the most famous neurotransmitters. (Prozac works on this guy.) It's obvious that DMT is very similar to this compound (this is common, especially amongst psychedelic drugs), and so one can surmise that DMT would behave in a manner substantially similar—but not identical—to serotonin and so temporarily alter brain function. Of course, the details are not fully known and, like anything in the brain, phenomenally complicated, but that's a reasonable way to think about it.
What's it like to take it? Let's ask McKenna:
What has impressed me repeatedly during my many glimpses into the world of the hallucinogenic indoles, and what seems generally to have escaped comment, is the transformation of narrative and language. The experience that engulfs one's entire being as one slips beneath the surface of the DMT ecstasy feels like the penetration of a membrane. The mind and the self literally unfold before one's eyes. There is a sense that one is made new, yet unchanged, as if one were made of gold and had just been recast in the furnace of one's birth. Breathing is normal, heartbeat steady, the mind clear and observing. But what of the world? What of incoming sensory data?(UPDATE: As B points out in comments, "indole" is the name for that fused ring system in DMT: the six-membered benzene ring attached to the five membered pyrrolidine ring.) I'm not sure if it's possible to write about a DMT trip without sounding like a New Age crystal-gazing lunatic. In any case, I couldn't find any better-sounding experiences online. People often report travel to alternate dimensions and contact with intelligent aliens.
Under the influence of DMT, the world becomes an Arabian labyrinth, a palace, a more than possible Martian jewel, vast with motifs that flood the gaping mind with complex and wordless awe. Color and the sense of a reality-unlocking secret nearby pervade the experience. There is a sense of other times, and of one's own infancy, and of wonder, wonder and more wonder. It is an audience with the alien nuncio. In the midst of this experience, apparently at the end of human history, guarding gates that seem surely to open on the howling maelstrom of the unspeakable emptiness between the stars, is the Aeon.
DMT is present in dozens of different plants throughout the world. Studies have found it occurring naturally in the human body; its function there is unknown so far, though that hasn't stopped some loopier types speculating that DMT may be at the root of some transcendental states achieved through meditation or religious fervor. It sounds plausible, but there is no confirming evidence as yet.
That's it for this week. Next week, we'll move from the tryptamine class of drugs to the phenethylamines.